Keeping Track of Bus Resources

XFree86 server 4.x Design (DRAFT) : Keeping Track of Bus Resources
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9. Keeping Track of Bus Resources

9.1. Theory of Operation

The XFree86 common layer has knowledge of generic access control mechanisms for devices on certain bus systems (currently the PCI bus) as well as of methods to enable or disable access to the buses itself. Furthermore it can access information on resources decoded by these devices and if necessary modify it.

When first starting the Xserver collects all this information, saves it for restoration, checks it for consistency, and if necessary, corrects it. Finally it disables all resources on a generic level prior to calling any driver function.

When the Probe() function of each driver is called the device sections are matched against the devices found in the system. The driver may probe devices at this stage that cannot be identified by using device independent methods. Access to all resources that can be controlled in a device independent way is disabled. The Probe() function should register all non-relocatable resources at this stage. If a resource conflict is found between exclusive resources the driver will fail immediately. Optionally the driver might specify an EntityInit(), EntityLeave() and EntityEnter() function.

EntityInit() can be used to disable any shared resources that are not controlled by the generic access control functions. It is called prior to the PreInit phase regardless if an entity is active or not. When calling the EntityInit(), EntityEnter() and EntityLeave() functions the common level will disable access to all other entities on a generic level. Since the common level has no knowledge of device specific methods to disable access to resources it cannot be guaranteed that certain resources are not decoded by any other entity until the EntityInit() or EntityEnter() phase is finished. Device drivers should therefore register all those resources which they are going to disable. If these resources are never to be used by any driver function they may be flagged ResInit so that they can be removed from the resource list after processing all EntityInit() functions. EntityEnter() should disable decoding of all resources which are not registered as exclusive and which are not handled by the generic access control in the common level. The difference to EntityInit() is that the latter one is only called once during lifetime of the server. It can therefore be used to set up variables prior to disabling resources. EntityLeave() should restore the original state when exiting the server or switching to a different VT. It also needs to disable device specific access functions if they need to be disabled on server exit or VT switch. The default state is to enable them before giving up the VT.

In PreInit() phase each driver should check if any sharable resources it has registered during Probe() has been denied and take appropriate action which could simply be to fail. If it needs to access resources it has disabled during EntitySetup() it can do so provided it has registered these and will disable them before returning from PreInit(). This also applies to all other driver functions. Several functions are provided to request resource ranges, register these, correct PCI config space and add replacements for the generic access functions. Resources may be marked ``disabled'' or ``unused'' during OPERATING stage. Although these steps could also be performed in ScreenInit(), this is not desirable.

Following PreInit() phase the common level determines if resource access control is needed. This is the case if more than one screen is used. If necessary the RAC wrapper module is loaded. In ScreenInit() the drivers can decide which operations need to be placed under RAC. Available are the frame buffer operations, the pointer operations and the colormap operations. Any operation that requires resources which might be disabled during OPERATING state should be set to use RAC. This can be specified separately for memory and IO resources.

When ScreenInit() phase is done the common level will determine which shared resources are requested by more than one driver and set the access functions accordingly. This is done following these rules:

The sharable resources registered by each entity are compared. If a resource is registered by more than one entity the entity will be marked to need to share this resources type (IO or MEM).
A resource marked ``disabled'' during OPERATING state will be ignored entirely.
A resource marked ``unused'' will only conflicts with an overlapping resource of an other entity if the second is actually in use during OPERATING state.
If an ``unused'' resource was found to conflict however the entity does not use any other resource of this type the entire resource type will be disabled for that entity.

The driver has the choice among different ways to control access to certain resources:

It can rely on the generic access functions. This is probably the most common case. Here the driver only needs to register any resource it is going to use.
It can replace the generic access functions by driver specific ones. This will mostly be used in cases where no generic access functions are available. In this case the driver has to make sure these resources are disabled when entering the PreInit() stage. Since the replacement functions are registered in PreInit() the driver will have to enable these resources itself if it needs to access them during this state. The driver can specify if the replacement functions can control memory and/or I/O resources separately.
The driver can enable resources itself when it needs them. Each driver function enabling them needs to disable them before it will return. This should be used if a resource which can be controlled in a device dependent way is only required during SETUP state. This way it can be marked ``unused'' during OPERATING state.

A resource which is decoded during OPERATING state however never accessed by the driver should be marked unused.

Since access switching latencies are an issue during Xserver operation, the common level attempts to minimize the number of entities that need to be placed under RAC control. When a wrapped operation is called, the EnableAccess() function is called before control is passed on. EnableAccess() checks if a screen is under access control. If not it just establishes bus routing and returns. If the screen needs to be under access control, EnableAccess() determines which resource types (MEM, IO) are required. Then it tests if this access is already established. If so it simply returns. If not it disables the currently established access, fixes bus routing and enables access to all entities registered for this screen.

Whenever a mode switch or a VT-switch is performed the common level will return to SETUP state.

9.2. Resource Types

Resource have certain properties. When registering resources each range is accompanied by a flag consisting of the ORed flags of the different properties the resource has. Each resource range may be classified according to

its physical properties i.e., if it addresses memory (ResMem) or I/O space (ResIo),
if it addresses a block (ResBlock) or sparse (ResSparse) range,
its access properties.

There are two known access properties:

ResExclusive for resources which may not be shared with any other device and
ResShared for resources which can be disabled and therefore can be shared.

If it is necessary to test a resource against any type a generic access type ResAny is provided. If this is set the resource will conflict with any resource of a different entity intersecting its range. Further it can be specified that a resource is decoded however never used during any stage (ResUnused) or during OPERATING state (ResUnusedOpr). A resource only visible during the init functions (ie. EntityInit(), EntityEnter() and EntityLeave() should be registered with the flag ResInit. A resource that might conflict with background resource ranges may be flagged with ResBios. This might be useful when registering resources ranges that were assigned by the system Bios.

Several predefined resource lists are available for VGA and 8514/A resources in common/xf86Resources.h.

9.3. Available Functions

The functions provided for resource management are listed in their order of use in the driver.

9.3.1. Probe Phase

In this phase each driver detects those resources it is able to drive, creates an entity record for each of them, registers non-relocatable resources and allocates screens and adds the resources to screens.

Two helper functions are provided for matching device sections in the xorg.conf file to the devices:

int xf86MatchPciInstances(const char *driverName, int vendorID, SymTabPtr chipsets, PciChipsets *PCIchipsets, GDevPtr *devList, int numDevs, DriverPtr drvp, int **foundEntities)

This function finds matches between PCI cards that a driver supports and config file device sections. It is intended for use in the ChipProbe() function of drivers for PCI cards. Only probed PCI devices with a vendor ID matching vendorID are considered. devList and numDevs are typically those found from calling xf86MatchDevice(), and represent the active config file device sections relevant to the driver. PCIchipsets is a table that provides a mapping between the PCI device IDs, the driver's internal chipset tokens and a list of fixed resources.

When a device section doesn't have a BusID entry it can only match the primary video device. Secondary devices are only matched with device sections that have a matching BusID entry.

Once the preliminary matches have been found, a final match is confirmed by checking if the chipset override, ChipID override or probed PCI chipset type match one of those given in the chipsets and PCIchipsets lists. The PCIchipsets list includes a list of the PCI device IDs supported by the driver. The list should be terminated with an entry with PCI ID -1". The chipsets list is a table mapping the driver's internal chipset tokens to names, and should be terminated with a NULL entry. Only those entries with a corresponding entry in the PCIchipsets list are considered. The order of precedence is: config file chipset, config file ChipID, probed PCI device ID.

In cases where a driver handles PCI chipsets with more than one vendor ID, it may set vendorID to 0, and OR each devID in the list with (the vendor ID << 16).

Entity index numbers for confirmed matches are returned as an array via foundEntities. The PCI information, chipset token and device section for each match are found in the EntityInfoRec referenced by the indices.

The function return value is the number of confirmed matches. A return value of -1 indicates an internal error. The returned foundEntities array should be freed by the driver with xfree() when it is no longer needed in cases where the return value is greater than zero.

int xf86MatchIsaInstances(const char *driverName, SymTabPtr chipsets, IsaChipsets *ISAchipsets, DriverPtr drvp, FindIsaDevProc FindIsaDevice, GDevPtr *devList, int numDevs, int **foundEntities)

This function finds matches between ISA cards that a driver supports and config file device sections. It is intended for use in the ChipProbe() function of drivers for ISA cards. devList and numDevs are typically those found from calling xf86MatchDevice(), and represent the active config file device sections relevant to the driver. ISAchipsets is a table that provides a mapping between the driver's internal chipset tokens and the resource classes. FindIsaDevice is a driver-provided function that probes the hardware and returns the chipset token corresponding to what was detected, and -1 if nothing was detected.

If the config file device section contains a chipset entry, then it is checked against the chipsets list. When no chipset entry is present, the FindIsaDevice function is called instead.

Entity index numbers for confirmed matches are returned as an array via foundEntities. The chipset token and device section for each match are found in the EntityInfoRec referenced by the indices.

The function return value is the number of confirmed matches. A return value of -1 indicates an internal error. The returned foundEntities array should be freed by the driver with xfree() when it is no longer needed in cases where the return value is greater than zero.

These two helper functions make use of several core functions that are available at the driver level:

Bool xf86ParsePciBusString(const char *busID, int *bus,           int *device, int *func)

Takes a BusID string, and if it is in the correct format, returns the PCI bus, device, func values that it indicates. The format of the string is expected to be "PCI:bus:device:func" where each of `bus', `device' and `func' are decimal integers. The ":func" part may be omitted, and the func value assumed to be zero, but this isn't encouraged. The "PCI" prefix may also be omitted. The prefix "AGP" is currently equivalent to the "PCI" prefix. If the string isn't a valid PCI BusID, the return value is FALSE.

Bool xf86ComparePciBusString(const char *busID, int bus,           int device, int func)

Compares a BusID string with PCI bus, device, func values. If they match TRUE is returned, and FALSE if they don't.

Bool xf86ParseIsaBusString(const char *busID)

Compares a BusID string with the ISA bus ID string ("ISA" or "ISA:"). If they match TRUE is returned, and FALSE if they don't.

Bool xf86CheckPciSlot(int bus, int device, int func)

Checks if the PCI slot bus:device:func has been claimed. If so, it returns FALSE, and otherwise TRUE.

int xf86ClaimPciSlot(int bus, int device, int func, DriverPtr drvp,           int chipset, GDevPtr dev, Bool active)

This function is used to claim a PCI slot, allocate the associated entity record and initialise their data structures. The return value is the index of the newly allocated entity record, or -1 if the claim fails. This function should always succeed if xf86CheckPciSlot() returned TRUE for the same PCI slot.

Bool xf86IsPrimaryPci(void)

This function returns TRUE if the primary card is a PCI device, and FALSE otherwise.

int xf86ClaimIsaSlot(DriverPtr drvp, int chipset,           GDevPtr dev, Bool active)

This allocates an entity record entity and initialise the data structures. The return value is the index of the newly allocated entity record.

Bool xf86IsPrimaryIsa(void)

This function returns TRUE if the primary card is an ISA (non-PCI) device, and FALSE otherwise.

Two helper functions are provided to aid configuring entities:

ScrnInfoPtr xf86ConfigPciEntity(ScrnInfoPtr pScrn,           int scrnFlag, int entityIndex,           PciChipsets *p_chip,           resList res, EntityProc init,           EntityProc enter, EntityProc leave,           pointer private)

ScrnInfoPtr xf86ConfigIsaEntity(ScrnInfoPtr pScrn,           int scrnFlag, int entityIndex,           IsaChipsets *i_chip,           resList res, EntityProc init,           EntityProc enter, EntityProc leave,           pointer private)

These functions are used to register the non-relocatable resources for an entity, and the optional entity-specific Init, Enter and Leave functions. Usually the list of fixed resources is obtained from the Isa/PciChipsets lists. However an additional list of resources may be passed. Generally this is not required. For active entities a ScrnInfoRec is allocated if the pScrn argument is NULL. The return value is TRUE when successful. The init, enter, leave functions are defined as follows:

typedef void (*EntityProc)(int entityIndex,           pointer private)

They are passed the entity index and a pointer to a private scratch area. This can be set up during Probe() and its address can be passed to xf86ConfigIsaEntity() and xf86ConfigPciEntity() as the last argument.

These two helper functions make use of several core functions that are available at the driver level:

void xf86ClaimFixedResources(resList list, int entityIndex)

This function registers the non-relocatable resources which cannot be disabled and which therefore would cause the server to fail immediately if they were found to conflict. It also records non-relocatable but sharable resources for processing after the Probe() phase.

Bool xf86SetEntityFuncs(int entityIndex, EntityProc init, EntityProc enter, EntityProc leave, pointer)

This function registers with an entity the init, enter, leave functions along with the pointer to their private area.

void xf86AddEntityToScreen(ScrnInfoPtr pScrn, int entityIndex)

This function associates the entity referenced by entityIndex with the screen.

9.3.2. PreInit Phase

During this phase the remaining resources should be registered. PreInit() should call xf86GetEntityInfo() to obtain a pointer to an EntityInfoRec for each entity it is able to drive and check if any resource are listed in its resources field. If resources registered in the Probe phase have been rejected in the post-Probe phase (resources is non-NULL), then the driver should decide if it can continue without using these or if it should fail.

EntityInfoPtr xf86GetEntityInfo(int entityIndex)

This function returns a pointer to the EntityInfoRec referenced by entityIndex. The returned EntityInfoRec should be freed with xfree() when no longer needed.

Several functions are provided to simplify resource registration:

Bool xf86IsEntityPrimary(int entityIndex)

This function returns TRUE if the entity referenced by entityIndex is the primary display device (i.e., the one initialised at boot time and used in text mode).

Bool xf86IsScreenPrimary(int scrnIndex)

This function returns TRUE if the primary entity is registered with the screen referenced by scrnIndex.

pciVideoPtr xf86GetPciInfoForEntity(int entityIndex)

This function returns a pointer to the pciVideoRec for the specified entity. If the entity is not a PCI device, NULL is returned.

The primary function for registration of resources is:

resPtr xf86RegisterResources(int entityIndex, resList list, int access)

This function tries to register the resources in list. If list is NULL it tries to determine the resources automatically. This only works for entities that provide a generic way to read out the resource ranges they decode. So far this is only the case for PCI devices. By default the PCI resources are registered as shared (ResShared) if the driver wants to set a different access type it can do so by specifying the access flags in the third argument. A value of 0 means to use the default settings. If for any reason the resource broker is not able to register some of the requested resources the function will return a pointer to a list of the failed ones. In this case the driver may be able to move the resource to different locations. In case of PCI bus entities this is done by passing the list of failed resources to xf86ReallocatePciResources(). When the registration succeeds, the return value is NULL.

resPtr xf86ReallocatePciResources(int entityIndex, resPtr pRes)

This function takes a list of PCI resources that need to be reallocated and returns NULL when all relocations are successful. xf86RegisterResources() should be called again to register the relocated resources with the broker. If the reallocation fails, a list of the resources that could not be relocated is returned.

Two functions are provided to obtain a resource range of a given type:

resRange xf86GetBlock(long type, memType size, memType window_start, memType window_end, memType align_mask, resPtr avoid)

This function tries to find a block range of size size and type type in a window bound by window_start and window_end with the alignment specified in align_mask. Optionally a list of resource ranges which should be avoided within the window can be supplied. On failure a zero-length range of type ResEnd will be returned.

resRange xf86GetSparse(long type, memType fixed_bits, memType decode_mask, memType address_mask, resPtr avoid)

This function is like the previous one, but attempts to find a sparse range instead of a block range. Here three values have to be specified: the address_mask which marks all bits of the mask part of the address, the decode_mask which masks out the bits which are hardcoded and are therefore not available for relocation and the values of the fixed bits. The function tries to find a base that satisfies the given condition. If the function fails it will return a zero range of type ResEnd. Optionally it might be passed a list of resource ranges to avoid.

Some PCI devices are broken in the sense that they return invalid size information for a certain resource. In this case the driver can supply the correct size and make sure that the resource range allocated for the card is large enough to hold the address range decoded by the card. The function xf86FixPciResource() can be used to do this:

Bool xf86FixPciResource(int entityIndex, unsigned int prt, CARD32 alignment, long type)

This function fixes a PCI resource allocation. The prt parameter contains the number of the PCI base register that needs to be fixed (0-5, and 6 for the BIOS base register). The size is specified by the alignment. Since PCI resources need to span an integral range of size 2ˆn, the alignment also specifies the number of addresses that will be decoded. If the driver specifies a type mask it can override the default type for PCI resources which is ResShared. The resource broker needs to know that to find a matching resource range. This function should be called before calling xf86RegisterResources(). The return value is TRUE when the function succeeds.

Bool xf86CheckPciMemBase(pciVideoPtr pPci, memType base)

This function checks that the memory base address specified matches one of the PCI base address register values for the given PCI device. This is mostly used to check that an externally provided base address (e.g., from a config file) matches an actual value allocated to a device.

The driver may replace the generic access control functions for an entity. This is done with the xf86SetAccessFuncs():

void xf86SetAccessFuncs(EntityInfoPtr pEnt, xf86SetAccessFuncPtr funcs, xf86SetAccessFuncPtr oldFuncs)

with:
      typedef struct {
          xf86AccessPtr mem;
          xf86AccessPtr io;
          xf86AccessPtr io_mem;
      } xf86SetAccessFuncRec, *xf86SetAccessFuncPtr;
    
The driver can pass three functions: one for I/O access, one for memory access and one for combined memory and I/O access. If the memory access and combined access functions are identical the common level assumes that the memory access cannot be controlled independently of I/O access, if the I/O access function and the combined access functions are the same it is assumed that I/O can not be controlled independently. If memory and I/O have to be controlled together all three values should be the same. If a non NULL value is passed as third argument it is interpreted as an address where to store the old access record. If the third argument is NULL it will be assumed that the generic access should be enabled before replacing the access functions. Otherwise it will be disabled. The driver may enable them itself using the returned values. It should do this from its replacement access functions as the generic access may be disabled by the common level on certain occasions. If replacement functions are specified they must control all resources of the specific type registered for the entity.

To find out if a specific resource range conflicts with another resource the xf86ChkConflict() function may be used:

memType xf86ChkConflict(resRange *rgp, int entityIndex)

This function checks if the resource range rgp of for the specified entity conflicts with with another resource. If a conflict is found, the address of the start of the conflict is returned. The return value is zero when there is no conflict.

The OPERATING state properties of previously registered fixed resources can be set with the xf86SetOperatingState() function:

resPtr xf86SetOperatingState(resList list, int entityIndex, int mask)

This function is used to set the status of a resource during OPERATING state. list holds a list to which mask is to be applied. The parameter mask may have the value ResUnusedOpr and ResDisableOpr. The first one should be used if a resource isn't used by the driver during OPERATING state although it is decoded by the device, while the latter one indicates that the resource is not decoded during OPERATING state. Note that the resource ranges have to match those specified during registration. If a range has been specified starting at A and ending at B and suppose C us a value satisfying A < C < B one may not specify the resource range (A,B) by splitting it into two ranges (A,C) and (C,B).

The following two functions are provided for special cases:

void xf86RemoveEntityFromScreen(ScrnInfoPtr pScrn, int entityIndex)

This function may be used to remove an entity from a screen. This only makes sense if a screen has more than one entity assigned or the screen is to be deleted. No test is made if the screen has any entities left.

void xf86DeallocateResourcesForEntity(int entityIndex, long type)

This function deallocates all resources of a given type registered for a certain entity from the resource broker list.

9.3.3. ScreenInit Phase

All that is required in this phase is to setup the RAC flags. Note that it is also permissible to set these flags up in the PreInit phase. The RAC flags are held in the racIoFlags and racMemFlags fields of the ScrnInfoRec for each screen. They specify which graphics operations might require the use of shared resources. This can be specified separately for memory and I/O resources. The available flags are defined in rac/xf86RAC.h. They are:

RAC_FB

for framebuffer operations (including hw acceleration)

RAC_CURSOR

for Cursor operations (??? I'm not sure if we need this for SW cursor it depends on which level the sw cursor is drawn)

RAC_COLORMAP

for colormap operations

RAC_VIEWPORT

for the call to ChipAdjustFrame()

The flags are ORed together.

XFree86 server 4.x Design (DRAFT) : Keeping Track of Bus Resources
Previous: Data and Data Structures
Next: Config file ``Option'' entries