Commit 302a2523 authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Bjorn Helgaas
Browse files

PCI/MSI: Add pci_enable_msi_range() and pci_enable_msix_range() 



This adds pci_enable_msi_range(), which supersedes the pci_enable_msi()
and pci_enable_msi_block() MSI interfaces.

It also adds pci_enable_msix_range(), which supersedes the
pci_enable_msix() MSI-X interface.

The old interfaces have three categories of return values:

    negative: failure; caller should not retry
    positive: failure; value indicates number of interrupts that *could*
	have been allocated, and caller may retry with a smaller request
    zero: success; at least as many interrupts allocated as requested

It is error-prone to handle these three cases correctly in drivers.

The new functions return either a negative error code or a number of
successfully allocated MSI/MSI-X interrupts, which is expected to lead to
clearer device driver code.

pci_enable_msi(), pci_enable_msi_block() and pci_enable_msix() still exist
unchanged, but are deprecated and may be removed after callers are updated.

[bhelgaas: tweak changelog]
Suggested-by: default avatarBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: default avatarAlexander Gordeev <agordeev@redhat.com>
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: default avatarTejun Heo <tj@kernel.org>
parent ff1aa430

Documentation/PCI/MSI-HOWTO.txt

+186 −75
Original line number Diff line number Diff line
@@ -82,67 +82,97 @@ Most of the hard work is done for the driver in the PCI layer. It simply 
has to request that the PCI layer set up the MSI capability for this

device.



4.2.1 pci_enable_msi

4.2.1 pci_enable_msi_range



int pci_enable_msi(struct pci_dev *dev)

int pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec)



A successful call allocates ONE interrupt to the device, regardless

of how many MSIs the device supports.  The device is switched from

pin-based interrupt mode to MSI mode.  The dev->irq number is changed

to a new number which represents the message signaled interrupt;

consequently, this function should be called before the driver calls

request_irq(), because an MSI is delivered via a vector that is

different from the vector of a pin-based interrupt.

This function allows a device driver to request any number of MSI

interrupts within specified range from 'minvec' to 'maxvec'.



4.2.2 pci_enable_msi_block

If this function returns a positive number it indicates the number of

MSI interrupts that have been successfully allocated.  In this case

the device is switched from pin-based interrupt mode to MSI mode and

updates dev->irq to be the lowest of the new interrupts assigned to it.

The other interrupts assigned to the device are in the range dev->irq

to dev->irq + returned value - 1.  Device driver can use the returned

number of successfully allocated MSI interrupts to further allocate

and initialize device resources.



int pci_enable_msi_block(struct pci_dev *dev, int count)

If this function returns a negative number, it indicates an error and

the driver should not attempt to request any more MSI interrupts for

this device.



This variation on the above call allows a device driver to request multiple

MSIs.  The MSI specification only allows interrupts to be allocated in

powers of two, up to a maximum of 2^5 (32).

This function should be called before the driver calls request_irq(),

because MSI interrupts are delivered via vectors that are different

from the vector of a pin-based interrupt.



If this function returns 0, it has succeeded in allocating at least as many

interrupts as the driver requested (it may have allocated more in order

to satisfy the power-of-two requirement).  In this case, the function

enables MSI on this device and updates dev->irq to be the lowest of

the new interrupts assigned to it.  The other interrupts assigned to

the device are in the range dev->irq to dev->irq + count - 1.

It is ideal if drivers can cope with a variable number of MSI interrupts;

there are many reasons why the platform may not be able to provide the

exact number that a driver asks for.



If this function returns a negative number, it indicates an error and

the driver should not attempt to request any more MSI interrupts for

this device.  If this function returns a positive number, it is

less than 'count' and indicates the number of interrupts that could have

been allocated.  In neither case is the irq value updated or the device

switched into MSI mode.



The device driver must decide what action to take if

pci_enable_msi_block() returns a value less than the number requested.

For instance, the driver could still make use of fewer interrupts;

in this case the driver should call pci_enable_msi_block()

again.  Note that it is not guaranteed to succeed, even when the

'count' has been reduced to the value returned from a previous call to

pci_enable_msi_block().  This is because there are multiple constraints

on the number of vectors that can be allocated; pci_enable_msi_block()

returns as soon as it finds any constraint that doesn't allow the

call to succeed.



4.2.3 pci_disable_msi

There could be devices that can not operate with just any number of MSI

interrupts within a range.  See chapter 4.3.1.3 to get the idea how to

handle such devices for MSI-X - the same logic applies to MSI.



4.2.1.1 Maximum possible number of MSI interrupts



The typical usage of MSI interrupts is to allocate as many vectors as

possible, likely up to the limit returned by pci_msi_vec_count() function:



static int foo_driver_enable_msi(struct pci_dev *pdev, int nvec)

{

	return pci_enable_msi_range(pdev, 1, nvec);

}



Note the value of 'minvec' parameter is 1.  As 'minvec' is inclusive,

the value of 0 would be meaningless and could result in error.



Some devices have a minimal limit on number of MSI interrupts.

In this case the function could look like this:



static int foo_driver_enable_msi(struct pci_dev *pdev, int nvec)

{

	return pci_enable_msi_range(pdev, FOO_DRIVER_MINIMUM_NVEC, nvec);

}



4.2.1.2 Exact number of MSI interrupts



If a driver is unable or unwilling to deal with a variable number of MSI

interrupts it could request a particular number of interrupts by passing

that number to pci_enable_msi_range() function as both 'minvec' and 'maxvec'

parameters:



static int foo_driver_enable_msi(struct pci_dev *pdev, int nvec)

{

	return pci_enable_msi_range(pdev, nvec, nvec);

}



4.2.1.3 Single MSI mode



The most notorious example of the request type described above is

enabling the single MSI mode for a device.  It could be done by passing

two 1s as 'minvec' and 'maxvec':



static int foo_driver_enable_single_msi(struct pci_dev *pdev)

{

	return pci_enable_msi_range(pdev, 1, 1);

}



4.2.2 pci_disable_msi



void pci_disable_msi(struct pci_dev *dev)



This function should be used to undo the effect of pci_enable_msi() or

pci_enable_msi_block().  Calling it restores dev->irq to the pin-based

interrupt number and frees the previously allocated message signaled

interrupt(s).  The interrupt may subsequently be assigned to another

device, so drivers should not cache the value of dev->irq.

This function should be used to undo the effect of pci_enable_msi_range().

Calling it restores dev->irq to the pin-based interrupt number and frees

the previously allocated MSIs.  The interrupts may subsequently be assigned

to another device, so drivers should not cache the value of dev->irq.



Before calling this function, a device driver must always call free_irq()

on any interrupt for which it previously called request_irq().

Failure to do so results in a BUG_ON(), leaving the device with

MSI enabled and thus leaking its vector.



4.2.4 pci_msi_vec_count

4.2.3 pci_msi_vec_count



int pci_msi_vec_count(struct pci_dev *dev)
@@ -176,26 +206,31 @@ in each element of the array to indicate for which entries the kernel 
should assign interrupts; it is invalid to fill in two entries with the

same number.



4.3.1 pci_enable_msix

4.3.1 pci_enable_msix_range



int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec)

int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,

			  int minvec, int maxvec)



Calling this function asks the PCI subsystem to allocate 'nvec' MSIs.

Calling this function asks the PCI subsystem to allocate any number of

MSI-X interrupts within specified range from 'minvec' to 'maxvec'.

The 'entries' argument is a pointer to an array of msix_entry structs

which should be at least 'nvec' entries in size.  On success, the

device is switched into MSI-X mode and the function returns 0.

The 'vector' member in each entry is populated with the interrupt number;

which should be at least 'maxvec' entries in size.



On success, the device is switched into MSI-X mode and the function

returns the number of MSI-X interrupts that have been successfully

allocated.  In this case the 'vector' member in entries numbered from

0 to the returned value - 1 is populated with the interrupt number;

the driver should then call request_irq() for each 'vector' that it

decides to use.  The device driver is responsible for keeping track of the

interrupts assigned to the MSI-X vectors so it can free them again later.

Device driver can use the returned number of successfully allocated MSI-X

interrupts to further allocate and initialize device resources.



If this function returns a negative number, it indicates an error and

the driver should not attempt to allocate any more MSI-X interrupts for

this device.  If it returns a positive number, it indicates the maximum

number of interrupt vectors that could have been allocated. See example

below.

this device.



This function, in contrast with pci_enable_msi(), does not adjust

This function, in contrast with pci_enable_msi_range(), does not adjust

dev->irq.  The device will not generate interrupts for this interrupt

number once MSI-X is enabled.
@@ -206,28 +241,103 @@ It is ideal if drivers can cope with a variable number of MSI-X interrupts; 
there are many reasons why the platform may not be able to provide the

exact number that a driver asks for.



A request loop to achieve that might look like:

There could be devices that can not operate with just any number of MSI-X

interrupts within a range.  E.g., an network adapter might need let's say

four vectors per each queue it provides.  Therefore, a number of MSI-X

interrupts allocated should be a multiple of four.  In this case interface

pci_enable_msix_range() can not be used alone to request MSI-X interrupts

(since it can allocate any number within the range, without any notion of

the multiple of four) and the device driver should master a custom logic

to request the required number of MSI-X interrupts.



4.3.1.1 Maximum possible number of MSI-X interrupts



The typical usage of MSI-X interrupts is to allocate as many vectors as

possible, likely up to the limit returned by pci_msix_vec_count() function:



static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec)

{

	while (nvec >= FOO_DRIVER_MINIMUM_NVEC) {

		rc = pci_enable_msix(adapter->pdev,

				     adapter->msix_entries, nvec);

		if (rc > 0)

			nvec = rc;

		else

			return rc;

	return pci_enable_msi_range(adapter->pdev, adapter->msix_entries,

				    1, nvec);

}



Note the value of 'minvec' parameter is 1.  As 'minvec' is inclusive,

the value of 0 would be meaningless and could result in error.



Some devices have a minimal limit on number of MSI-X interrupts.

In this case the function could look like this:



static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec)

{

	return pci_enable_msi_range(adapter->pdev, adapter->msix_entries,

				    FOO_DRIVER_MINIMUM_NVEC, nvec);

}



4.3.1.2 Exact number of MSI-X interrupts



If a driver is unable or unwilling to deal with a variable number of MSI-X

interrupts it could request a particular number of interrupts by passing

that number to pci_enable_msix_range() function as both 'minvec' and 'maxvec'

parameters:



static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec)

{

	return pci_enable_msi_range(adapter->pdev, adapter->msix_entries,

				    nvec, nvec);

}



4.3.1.3 Specific requirements to the number of MSI-X interrupts



As noted above, there could be devices that can not operate with just any

number of MSI-X interrupts within a range.  E.g., let's assume a device that

is only capable sending the number of MSI-X interrupts which is a power of

two.  A routine that enables MSI-X mode for such device might look like this:



/*

 * Assume 'minvec' and 'maxvec' are non-zero

 */

static int foo_driver_enable_msix(struct foo_adapter *adapter,

				  int minvec, int maxvec)

{

	int rc;



	minvec = roundup_pow_of_two(minvec);

	maxvec = rounddown_pow_of_two(maxvec);



	if (minvec > maxvec)

		return -ERANGE;



retry:

	rc = pci_enable_msix_range(adapter->pdev, adapter->msix_entries,

				   maxvec, maxvec);

	/*

	 * -ENOSPC is the only error code allowed to be analized

	 */

	if (rc == -ENOSPC) {

		if (maxvec == 1)

			return -ENOSPC;



		maxvec /= 2;



		if (minvec > maxvec)

			return -ENOSPC;



		goto retry;

	}



	return rc;

}



Note how pci_enable_msix_range() return value is analized for a fallback -

any error code other than -ENOSPC indicates a fatal error and should not

be retried.



4.3.2 pci_disable_msix



void pci_disable_msix(struct pci_dev *dev)



This function should be used to undo the effect of pci_enable_msix().  It frees

the previously allocated message signaled interrupts.  The interrupts may

This function should be used to undo the effect of pci_enable_msix_range().

It frees the previously allocated MSI-X interrupts. The interrupts may

subsequently be assigned to another device, so drivers should not cache

the value of the 'vector' elements over a call to pci_disable_msix().
@@ -261,13 +371,14 @@ number of MSI-X interrupt vectors that could be allocated. 
If a device implements both MSI and MSI-X capabilities, it can

run in either MSI mode or MSI-X mode, but not both simultaneously.

This is a requirement of the PCI spec, and it is enforced by the

PCI layer.  Calling pci_enable_msi() when MSI-X is already enabled or

pci_enable_msix() when MSI is already enabled results in an error.

If a device driver wishes to switch between MSI and MSI-X at runtime,

it must first quiesce the device, then switch it back to pin-interrupt

mode, before calling pci_enable_msi() or pci_enable_msix() and resuming

operation.  This is not expected to be a common operation but may be

useful for debugging or testing during development.

PCI layer.  Calling pci_enable_msi_range() when MSI-X is already

enabled or pci_enable_msix_range() when MSI is already enabled

results in an error.  If a device driver wishes to switch between MSI

and MSI-X at runtime, it must first quiesce the device, then switch

it back to pin-interrupt mode, before calling pci_enable_msi_range()

or pci_enable_msix_range() and resuming operation.  This is not expected

to be a common operation but may be useful for debugging or testing

during development.



4.5 Considerations when using MSIs
@@ -382,5 +493,5 @@ or disabled (0). If 0 is found in any of the msi_bus files belonging 
to bridges between the PCI root and the device, MSIs are disabled.



It is also worth checking the device driver to see whether it supports MSIs.

For example, it may contain calls to pci_enable_msi(), pci_enable_msix() or

pci_enable_msi_block().
 
For example, it may contain calls to pci_enable_msi_range() or

pci_enable_msix_range().

drivers/pci/msi.c

+74 −0
Original line number Diff line number Diff line
@@ -1102,3 +1102,77 @@ void pci_msi_init_pci_dev(struct pci_dev *dev) 
	if (dev->msix_cap)

		msix_set_enable(dev, 0);

}



/**

 * pci_enable_msi_range - configure device's MSI capability structure

 * @dev: device to configure

 * @minvec: minimal number of interrupts to configure

 * @maxvec: maximum number of interrupts to configure

 *

 * This function tries to allocate a maximum possible number of interrupts in a

 * range between @minvec and @maxvec. It returns a negative errno if an error

 * occurs. If it succeeds, it returns the actual number of interrupts allocated

 * and updates the @dev's irq member to the lowest new interrupt number;

 * the other interrupt numbers allocated to this device are consecutive.

 **/

int pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec)

{

	int nvec = maxvec;

	int rc;



	if (maxvec < minvec)

		return -ERANGE;



	do {

		rc = pci_enable_msi_block(dev, nvec);

		if (rc < 0) {

			return rc;

		} else if (rc > 0) {

			if (rc < minvec)

				return -ENOSPC;

			nvec = rc;

		}

	} while (rc);



	return nvec;

}

EXPORT_SYMBOL(pci_enable_msi_range);



/**

 * pci_enable_msix_range - configure device's MSI-X capability structure

 * @dev: pointer to the pci_dev data structure of MSI-X device function

 * @entries: pointer to an array of MSI-X entries

 * @minvec: minimum number of MSI-X irqs requested

 * @maxvec: maximum number of MSI-X irqs requested

 *

 * Setup the MSI-X capability structure of device function with a maximum

 * possible number of interrupts in the range between @minvec and @maxvec

 * upon its software driver call to request for MSI-X mode enabled on its

 * hardware device function. It returns a negative errno if an error occurs.

 * If it succeeds, it returns the actual number of interrupts allocated and

 * indicates the successful configuration of MSI-X capability structure

 * with new allocated MSI-X interrupts.

 **/

int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,

			       int minvec, int maxvec)

{

	int nvec = maxvec;

	int rc;



	if (maxvec < minvec)

		return -ERANGE;



	do {

		rc = pci_enable_msix(dev, entries, nvec);

		if (rc < 0) {

			return rc;

		} else if (rc > 0) {

			if (rc < minvec)

				return -ENOSPC;

			nvec = rc;

		}

	} while (rc);



	return nvec;

}

EXPORT_SYMBOL(pci_enable_msix_range);

include/linux/pci.h

+14 −0
Original line number Diff line number Diff line
@@ -1193,6 +1193,17 @@ static inline int pci_msi_enabled(void) 
{

	return 0;

}



static inline int pci_enable_msi_range(struct pci_dev *dev, int minvec,

				       int maxvec)

{

	return -ENOSYS;

}

static inline int pci_enable_msix_range(struct pci_dev *dev,

		      struct msix_entry *entries, int minvec, int maxvec)

{

	return -ENOSYS;

}

#else

int pci_msi_vec_count(struct pci_dev *dev);

int pci_enable_msi_block(struct pci_dev *dev, int nvec);
@@ -1205,6 +1216,9 @@ void pci_disable_msix(struct pci_dev *dev); 
void msi_remove_pci_irq_vectors(struct pci_dev *dev);

void pci_restore_msi_state(struct pci_dev *dev);

int pci_msi_enabled(void);

int pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec);

int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,

			  int minvec, int maxvec);

#endif



#ifdef CONFIG_PCIEPORTBUS

CRA Git | Maintained and supported by SUSTech CRA and CCSE