Re: [PATCH v6 2/9] PCI/ACPI: Add _OSC based negotiation support for DPC

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jul 26, 2019 at 02:43:12PM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> 
> As per PCI firmware specification r3.2 Downstream Port Containment
> Related Enhancements ECN, sec 4.5.1, table 4-6, OS can use bit 7 of _OSC
> Control Field to negotiate control over Downstream Port Containment
> (DPC) configuration of PCIe port.
> 
> After _OSC negotiation, firmware will Set this bit to grant OS control
> over PCIe DPC configuration and Clear it if this feature was requested
> and denied, or was not requested.
> 
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Len Brown <lenb@kernel.org>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> ---
>  drivers/acpi/pci_root.c         | 6 ++++++
>  drivers/pci/pcie/portdrv_core.c | 3 ++-
>  drivers/pci/probe.c             | 1 +
>  include/linux/acpi.h            | 3 ++-
>  include/linux/pci.h             | 2 +-
>  5 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 314a187ed572..73b08f40b0da 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -142,6 +142,7 @@ static struct pci_osc_bit_struct pci_osc_control_bit[] = {
>  	{ OSC_PCI_EXPRESS_AER_CONTROL, "AER" },
>  	{ OSC_PCI_EXPRESS_CAPABILITY_CONTROL, "PCIeCapability" },
>  	{ OSC_PCI_EXPRESS_LTR_CONTROL, "LTR" },
> +	{ OSC_PCI_EXPRESS_DPC_CONTROL, "DPC" },
>  };
>  
>  static void decode_osc_bits(struct acpi_pci_root *root, char *msg, u32 word,
> @@ -488,6 +489,9 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
>  			control |= OSC_PCI_EXPRESS_AER_CONTROL;
>  	}
>  
> +	if (IS_ENABLED(CONFIG_PCIE_DPC))
> +		control |= OSC_PCI_EXPRESS_DPC_CONTROL;

Sec 4.5.2.4 says:

  If the OS sets bit 7 of the Control field, it must set bit 7 of the
  Support field, indicating support for the Error Disconnect Recover
  event.

I see that you do set bit 7 (OSC_PCI_EDR_SUPPORT) in the Support field
in a later patch, but I don't think we should have this intermediate
state where we set OSC_PCI_EXPRESS_DPC_CONTROL in Control but not
OSC_PCI_EDR_SUPPORT in Support.

>  	requested = control;
>  	status = acpi_pci_osc_control_set(handle, &control,
>  					  OSC_PCI_EXPRESS_CAPABILITY_CONTROL);
> @@ -917,6 +921,8 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>  		host_bridge->native_pme = 0;
>  	if (!(root->osc_control_set & OSC_PCI_EXPRESS_LTR_CONTROL))
>  		host_bridge->native_ltr = 0;
> +	if (!(root->osc_control_set & OSC_PCI_EXPRESS_DPC_CONTROL))
> +		host_bridge->native_dpc = 0;
>  
>  	/*
>  	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
> diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
> index 308c3e0c4a34..58c40fe7856f 100644
> --- a/drivers/pci/pcie/portdrv_core.c
> +++ b/drivers/pci/pcie/portdrv_core.c
> @@ -252,7 +252,8 @@ static int get_port_device_capability(struct pci_dev *dev)
>  	}
>  
>  	if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
> -	    pci_aer_available() && services & PCIE_PORT_SERVICE_AER)
> +	    pci_aer_available() && services & PCIE_PORT_SERVICE_AER &&
> +	    (pcie_ports_native || host->native_dpc))
>  		services |= PCIE_PORT_SERVICE_DPC;
>  
>  	if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index a3c7338fad86..cf8acdd62089 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -601,6 +601,7 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge)
>  	bridge->native_shpc_hotplug = 1;
>  	bridge->native_pme = 1;
>  	bridge->native_ltr = 1;
> +	bridge->native_dpc = 1;
>  }
>  
>  struct pci_host_bridge *pci_alloc_host_bridge(size_t priv)
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 9426b9aaed86..8959ed322e15 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -525,7 +525,8 @@ extern bool osc_pc_lpi_support_confirmed;
>  #define OSC_PCI_EXPRESS_AER_CONTROL		0x00000008
>  #define OSC_PCI_EXPRESS_CAPABILITY_CONTROL	0x00000010
>  #define OSC_PCI_EXPRESS_LTR_CONTROL		0x00000020
> -#define OSC_PCI_CONTROL_MASKS			0x0000003f
> +#define OSC_PCI_EXPRESS_DPC_CONTROL		0x00000080
> +#define OSC_PCI_CONTROL_MASKS			0x000000ff

You added 0x80, but 0x3f | 0x80 == 0xbf, not 0xff, so I expected
OSC_PCI_CONTROL_MASKS would change to 0xbf.  Why the difference?

>  #define ACPI_GSB_ACCESS_ATTRIB_QUICK		0x00000002
>  #define ACPI_GSB_ACCESS_ATTRIB_SEND_RCV         0x00000004
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 9e700d9f9f28..9145136ca728 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -510,7 +510,7 @@ struct pci_host_bridge {
>  	unsigned int	native_pme:1;		/* OS may use PCIe PME */
>  	unsigned int	native_ltr:1;		/* OS may use PCIe LTR */
>  	unsigned int	preserve_config:1;	/* Preserve FW resource setup */
> -
> +	unsigned int	native_dpc:1;		/* OS may use PCIe DPC */

Please put this next to the other "native_*" bits and preserve the
blank line.

>  	/* Resource alignment requirements */
>  	resource_size_t (*align_resource)(struct pci_dev *dev,
>  			const struct resource *res,
> -- 
> 2.21.0
>