linux-kernel - Re: [PATCH v1] PCI/EDR: Align EDR implementation with PCI firmware r3.3 spec

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Date: Wed, 1 May 2024 16:50:09 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Thatchanamurthy Satish <Satish.Thatchanamurt@...l.com>
Subject: Re: [PATCH v1] PCI/EDR: Align EDR implementation with PCI firmware
 r3.3 spec

On Wed, May 01, 2024 at 02:25:43AM +0000, Kuppuswamy Sathyanarayanan wrote:
> During the Error Disconnect Recover (EDR) spec transition from r3.2 ECN
> to PCI firmware spec r3.3, improvements were made to definitions of
> EDR_PORT_DPC_ENABLE_DSM (0x0C) and EDR_PORT_LOCATE_DSM(0x0D) _DSMs.
> 
> Specifically,
> 
> * EDR_PORT_DPC_ENABLE_DSM _DSM version changed from 5 to 6, and
>   arg4 is now a package type instead of an integer in version 5.
> * EDR_PORT_LOCATE_DSM _DSM uses BIT(31) to return the status of the
>   operation.
> 
> Ensure _DSM implementation aligns with PCI firmware r3.3 spec
> recommendation. More details about the EDR_PORT_DPC_ENABLE_DSM and
> EDR_PORT_LOCATE_DSM _DSMs can be found in PCI firmware specification,
> r3.3, sec 4.6.12 and sec 4.6.13.
>
> While at it, fix a typo in EDR_PORT_LOCATE_DSM comments.
> 
> Fixes: ac1c8e35a326 ("PCI/DPC: Add Error Disconnect Recover (EDR) support")
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
>  drivers/pci/pcie/edr.c | 23 +++++++++++++++++------
>  1 file changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/pcie/edr.c b/drivers/pci/pcie/edr.c
> index 5f4914d313a1..fea098e22e3e 100644
> --- a/drivers/pci/pcie/edr.c
> +++ b/drivers/pci/pcie/edr.c
> @@ -35,7 +35,7 @@ static int acpi_enable_dpc(struct pci_dev *pdev)
>  	 * Behavior when calling unsupported _DSM functions is undefined,
>  	 * so check whether EDR_PORT_DPC_ENABLE_DSM is supported.
>  	 */
> -	if (!acpi_check_dsm(adev->handle, &pci_acpi_dsm_guid, 5,
> +	if (!acpi_check_dsm(adev->handle, &pci_acpi_dsm_guid, 6,
>  			    1ULL << EDR_PORT_DPC_ENABLE_DSM))

How confident are we that this won't break any existing platforms?
Any idea how many platforms implement EDR_PORT_DPC_ENABLE_DSM and what
Revision IDs they support?

>  		return 0;
>  
> @@ -47,11 +47,11 @@ static int acpi_enable_dpc(struct pci_dev *pdev)
>  	argv4.package.elements = &req;
>  
>  	/*
> -	 * Per Downstream Port Containment Related Enhancements ECN to PCI
> -	 * Firmware Specification r3.2, sec 4.6.12, EDR_PORT_DPC_ENABLE_DSM is
> -	 * optional.  Return success if it's not implemented.
> +	 * Per PCI Firmware Specification r3.3, sec 4.6.12,
> +	 * EDR_PORT_DPC_ENABLE_DSM is optional. Return success if it's not
> +	 * implemented.
>  	 */
> -	obj = acpi_evaluate_dsm(adev->handle, &pci_acpi_dsm_guid, 5,
> +	obj = acpi_evaluate_dsm(adev->handle, &pci_acpi_dsm_guid, 6,
>  				EDR_PORT_DPC_ENABLE_DSM, &argv4);
>  	if (!obj)
>  		return 0;
> @@ -86,7 +86,7 @@ static struct pci_dev *acpi_dpc_port_get(struct pci_dev *pdev)
>  
>  	/*
>  	 * Behavior when calling unsupported _DSM functions is undefined,
> -	 * so check whether EDR_PORT_DPC_ENABLE_DSM is supported.
> +	 * so check whether EDR_PORT_LOCATE_DSM is supported.
>  	 */
>  	if (!acpi_check_dsm(adev->handle, &pci_acpi_dsm_guid, 5,
>  			    1ULL << EDR_PORT_LOCATE_DSM))
> @@ -103,6 +103,17 @@ static struct pci_dev *acpi_dpc_port_get(struct pci_dev *pdev)
>  		return NULL;
>  	}
>  
> +	/*
> +	 * Per PCI Firmware Specification r3.3, sec 4.6.13, bit 31 represents
> +	 * the success/failure of the operation. If bit 31 is set, the operation
> +	 * is failed.
> +	 */
> +	if (obj->integer.value & BIT(31)) {
> +		ACPI_FREE(obj);
> +		pci_err(pdev, "Locate Port _DSM failed\n");
> +		return NULL;
> +	}

This changes two _DSMs, and I think it should be two patches.

Same question here: we now depend on functionality we didn't depend on
before.  How confident are we in this?

>  	/*
>  	 * Firmware returns DPC port BDF details in following format:
>  	 *	15:8 = bus
> -- 
> 2.25.1
>