linux-kernel - Re: [PATCH v12 8/8] PCI/ACPI: Enable EDR support

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Date:   Fri, 17 Jan 2020 14:41:15 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     sathyanarayanan.kuppuswamy@...ux.intel.com
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...el.com, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Keith Busch <keith.busch@...el.com>,
        Huong Nguyen <huong.nguyen@...l.com>,
        Austin Bolen <Austin.Bolen@...l.com>
Subject: Re: [PATCH v12 8/8] PCI/ACPI: Enable EDR support

On Sun, Jan 12, 2020 at 02:44:02PM -0800, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> As per PCI firmware specification r3.2 Downstream Port Containment
> Related Enhancements ECN, sec 4.5.1, OS must implement following steps
> to enable/use EDR feature.
> 
> 1. 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.
> 
> 2. Also, if OS supports EDR, it should expose its support to BIOS by
> setting bit 7 of _OSC Support Field. And if OS sets bit 7 of _OSC
> Control Field it must also expose support for EDR by setting bit 7 of
> _OSC Support Field.

> --- a/drivers/pci/pcie/portdrv_core.c
> +++ b/drivers/pci/pcie/portdrv_core.c
> @@ -253,10 +253,13 @@ static int get_port_device_capability(struct pci_dev *dev)
>  	/*
>  	 * With dpc-native, allow Linux to use DPC even if it doesn't have
>  	 * permission to use AER.
> +	 * If EDR support is enabled in OS, then even if AER is not handled in
> +	 * OS, DPC service can be enabled.

Can you clarify this comment?  It talks about AER, but the code you
added:

  (IS_ENABLED(CONFIG_PCIE_EDR) && !host->native_dpc)

doesn't have anything to do with AER.

>  	 */
>  	if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
> -	    pci_aer_available() &&
> -	    (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))
> +	    ((IS_ENABLED(CONFIG_PCIE_EDR) && !host->native_dpc) ||
> +	    (pci_aer_available() &&
> +	    (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))))
>  		services |= PCIE_PORT_SERVICE_DPC;