Re: [PATCH] PCI PCIe portdrv: Fix allocation of interrupts (rev. 3)

[Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>]

Rafael J. Wysocki wrote:
> Hi,
> 
> The patch below fixes the problem with MSI-X vectors allocation by the PCIe
> port driver.  It applies on top of the series of PCIe port driver cleanups and
> bug fixes I've just sent.
> 
> Please review.
> 

The patch seems to still have the following assumptions.

 - The number of MSI-X table entries is less than or equal to two.
 - MSI-X table entries are mapped only to PME/HP and/or AER.

Thanks,
Kenji Kaneshige


> Thanks,
> Rafael
> 
> ---
> Subject: PCI PCIe portdrv: Fix allocation of interrupts (rev. 3)
> From: Rafael J. Wysocki <rjw@sisk.pl>
> 
> If MSI-X interrupt mode is used by the PCI Express port driver, too
> many vectors are allocated and it is not ensured that the right
> vectors will be used for the right services.  Namely, the PCI Express
> specification states that both PCI Express native PME and PCI Express
> hotplug will always use the same MSI or MSI-X message for signalling
> interrupts, which implies that the same vector will be used by both
> of them.  Also, the VC service does not use interrupts at all.
> Moreover, is not clear which of the vectors allocated by
> pci_enable_msix() will be used for PME and hotplug and which of them
> will be used for AER if all of these services are configured.
> 
> For these reasons, rework the allocation of interrupts for PCI
> Express ports so that at most two vectors are allocated and ensure
> that the right vector will be used for the right purpose.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> ---
>  drivers/pci/pcie/portdrv.h      |    2 
>  drivers/pci/pcie/portdrv_core.c |  142 +++++++++++++++++++++++++++++-----------
>  include/linux/pcieport_if.h     |   12 ++-
>  3 files changed, 114 insertions(+), 42 deletions(-)
> 
> Index: linux-2.6/drivers/pci/pcie/portdrv_core.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pcie/portdrv_core.c
> +++ linux-2.6/drivers/pci/pcie/portdrv_core.c
> @@ -31,6 +31,72 @@ static void release_pcie_device(struct d
>  }
>  
>  /**
> + * pcie_port_enable_msix - try to set up MSI-X as interrupt mode for given port
> + * @dev: PCI Express port to handle
> + * @vectors: Array of interrupt vectors to populate
> + * @nvec: Number of interrupt vectors to allocate
> + *
> + * Return value: 0 on success, error code on failure
> + */
> +static int pcie_port_enable_msix(struct pci_dev *dev, int *vectors, int nvec)
> +{
> +	struct msix_entry msix_entries[PCIE_PORT_DEVICE_MAXINTERRUPTS] = {
> +		{ 0, },
> +	};
> +	int status, pos, i;
> +	u16 reg16;
> +	u32 reg32;
> +
> +	for (i = 0; i < nvec; i++)
> +		msix_entries[i].entry = i;
> +
> +	status = pci_enable_msix(dev, msix_entries, nvec);
> +	if (status)
> +		return status;
> +
> +	/*
> +	 * The code below follows the PCI Express Base Specification 2.0 clearly
> +	 * stating in Section 6.1.6 that "PME and Hot-Plug Event interrupts
> +	 * (when both are implemented) always share the same MSI or MSI-X
> +	 * vector, as indicated by the Interrupt Message Number field in the PCI
> +	 * Express Capabilities register", where according to Section 7.8.2 of
> +	 * the Specification "For MSI-X, the value in this field indicates which
> +	 * MSI-X Table entry is used to generate the interrupt message."
> +	 */
> +	pos = pci_find_capability(dev, PCI_CAP_ID_EXP);
> +	pci_read_config_word(dev, pos + PCIE_CAPABILITIES_REG, &reg16);
> +	i = (reg16 >> 9) & PCIE_PORT_MSI_VECTOR_MASK;
> +	if (i >= nvec) {
> +		goto Error;
> +	} else {
> +		vectors[PCIE_PORT_SERVICE_PME_SHIFT] = msix_entries[i].vector;
> +		vectors[PCIE_PORT_SERVICE_HP_SHIFT] = msix_entries[i].vector;
> +	}
> +
> +	/*
> +	 * The code below follows Section 7.10.10 of the PCI Express Base
> +	 * Specification 2.0 stating that bits 31-27 of the Root Error Status
> +	 * Register contain a value indicating which of the MSI/MSI-X vectors
> +	 * assigned to the port is going to be used for AER, where "For MSI-X,
> +	 * the value in this register indicates which MSI-X Table entry is used
> +	 * to generate the interrupt message."
> +	 */
> +	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ERR);
> +	pci_read_config_dword(dev, pos + PCI_ERR_ROOT_STATUS, &reg32);
> +	i = (reg32 >> 27) & PCIE_PORT_MSI_VECTOR_MASK;
> +	if (i >= nvec)
> +		goto Error;
> +	else
> +		vectors[PCIE_PORT_SERVICE_AER_SHIFT] = msix_entries[i].vector;
> +
> +	return 0;
> +
> + Error:
> +	pci_disable_msix(dev);
> +	return -EIO;
> +}
> +
> +/**
>   * assign_interrupt_mode - choose interrupt mode for PCI Express port services
>   *                         (INTx, MSI-X, MSI) and set up vectors
>   * @dev: PCI Express port to handle
> @@ -42,49 +108,49 @@ static void release_pcie_device(struct d
>  static int assign_interrupt_mode(struct pci_dev *dev, int *vectors, int mask)
>  {
>  	struct pcie_port_data *port_data = pci_get_drvdata(dev);
> -	int i, pos, nvec, status = -EINVAL;
> -	int interrupt_mode = PCIE_PORT_NO_IRQ;
> +	int nvec, irq, interrupt_mode = PCIE_PORT_NO_IRQ;
> +	int i;
>  
> -	/* Set INTx as default */
> -	for (i = 0, nvec = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++) {
> -		if (mask & (1 << i)) 
> -			nvec++;
> -		vectors[i] = dev->irq;
> -	}
> -	if (dev->pin)
> -		interrupt_mode = PCIE_PORT_INTx_MODE;
> +	/*
> +	 * Determine the number of vectors to allocate.
> +	 *
> +	 * According to the PCI Express specification both PME and PCI Express
> +	 * hotplug always use the same interrupt vector, while AER can use
> +	 * a different one.
> +	 */
> +	nvec = 0;
> +	if (mask & (PCIE_PORT_SERVICE_PME | PCIE_PORT_SERVICE_HP))
> +		nvec++;
> +	if (mask & PCIE_PORT_SERVICE_AER)
> +		nvec++;
> +	if (!nvec)
> +		return PCIE_PORT_NO_IRQ;
>  
>  	/* Check MSI quirk */
>  	if (port_data->port_type == PCIE_RC_PORT && pcie_mch_quirk)
> -		return interrupt_mode;
> +		goto Fallback;
> +
> +	/* For nvec > 1 use MSI-X if supported */
> +	if (nvec > 1 && !pcie_port_enable_msix(dev, vectors, nvec)) {
> +		interrupt_mode = PCIE_PORT_MSIX_MODE;
> +		goto Exit;
> +	}
> +
> +	/* We're not going to use MSI-X, so try MSI and fall back to INTx */
> +	if (!pci_enable_msi(dev))
> +		interrupt_mode = PCIE_PORT_MSI_MODE;
> +
> + Fallback:
> +	if (interrupt_mode == PCIE_PORT_NO_IRQ && dev->pin)
> +		interrupt_mode = PCIE_PORT_INTx_MODE;
> +
> +	irq = interrupt_mode != PCIE_PORT_NO_IRQ ? dev->irq : -1;
> +	for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++)
> +		vectors[i] = irq;
> +
> + Exit:
> +	vectors[PCIE_PORT_SERVICE_VC_SHIFT] = -1;
>  
> -	/* Select MSI-X over MSI if supported */		
> -	pos = pci_find_capability(dev, PCI_CAP_ID_MSIX);
> -	if (pos) {
> -		struct msix_entry msix_entries[PCIE_PORT_DEVICE_MAXSERVICES] = 
> -			{{0, 0}, {0, 1}, {0, 2}, {0, 3}};
> -		status = pci_enable_msix(dev, msix_entries, nvec);
> -		if (!status) {
> -			int j = 0;
> -
> -			interrupt_mode = PCIE_PORT_MSIX_MODE;
> -			for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++) {
> -				if (mask & (1 << i)) 
> -					vectors[i] = msix_entries[j++].vector;
> -			}
> -		}
> -	} 
> -	if (status) {
> -		pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
> -		if (pos) {
> -			status = pci_enable_msi(dev);
> -			if (!status) {
> -				interrupt_mode = PCIE_PORT_MSI_MODE;
> -				for (i = 0;i < PCIE_PORT_DEVICE_MAXSERVICES;i++)
> -					vectors[i] = dev->irq;
> -			}
> -		}
> -	} 
>  	return interrupt_mode;
>  }
>  
> Index: linux-2.6/include/linux/pcieport_if.h
> ===================================================================
> --- linux-2.6.orig/include/linux/pcieport_if.h
> +++ linux-2.6/include/linux/pcieport_if.h
> @@ -16,10 +16,14 @@
>  #define PCIE_ANY_PORT			7
>  
>  /* Service Type */
> -#define PCIE_PORT_SERVICE_PME		1	/* Power Management Event */
> -#define PCIE_PORT_SERVICE_AER		2	/* Advanced Error Reporting */
> -#define PCIE_PORT_SERVICE_HP		4	/* Native Hotplug */
> -#define PCIE_PORT_SERVICE_VC		8	/* Virtual Channel */
> +#define PCIE_PORT_SERVICE_PME_SHIFT	0	/* Power Management Event */
> +#define PCIE_PORT_SERVICE_PME		(1 << PCIE_PORT_SERVICE_PME_SHIFT)
> +#define PCIE_PORT_SERVICE_AER_SHIFT	1	/* Advanced Error Reporting */
> +#define PCIE_PORT_SERVICE_AER		(1 << PCIE_PORT_SERVICE_AER_SHIFT)
> +#define PCIE_PORT_SERVICE_HP_SHIFT	2	/* Native Hotplug */
> +#define PCIE_PORT_SERVICE_HP		(1 << PCIE_PORT_SERVICE_HP_SHIFT)
> +#define PCIE_PORT_SERVICE_VC_SHIFT	3	/* Virtual Channel */
> +#define PCIE_PORT_SERVICE_VC		(1 << PCIE_PORT_SERVICE_VC_SHIFT)
>  
>  /* Root/Upstream/Downstream Port's Interrupt Mode */
>  #define PCIE_PORT_NO_IRQ		(-1)
> Index: linux-2.6/drivers/pci/pcie/portdrv.h
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pcie/portdrv.h
> +++ linux-2.6/drivers/pci/pcie/portdrv.h
> @@ -25,6 +25,8 @@
>  #define PCIE_CAPABILITIES_REG		0x2
>  #define PCIE_SLOT_CAPABILITIES_REG	0x14
>  #define PCIE_PORT_DEVICE_MAXSERVICES	4
> +#define PCIE_PORT_DEVICE_MAXINTERRUPTS	2
> +#define PCIE_PORT_MSI_VECTOR_MASK	0x1f
>  
>  #define get_descriptor_id(type, service) (((type - 4) << 4) | service)
>  
> 
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