linux-kernel - Re: [PATCHv3] PCI/ACPI: _DSM PRESERVE_BOOT_CONFIG function rev id doesn't match with spec

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Message-Id: <20241216015115.24075-1-zhoushengqing@ttyinfo.com>
Date: Mon, 16 Dec 2024 01:51:15 +0000
From: Zhou Shengqing <zhoushengqing@...info.com>
To: bhelgaas@...gle.com
Cc: zhoushengqing@...info.com,
	lenb@...nel.org,
	linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCHv3] PCI/ACPI: _DSM PRESERVE_BOOT_CONFIG function rev id doesn't match with spec

Hi Bjorn,
  Please ignore this post.

On Sat, 14 Dec 2024 10:41:17 +0000, Zhou shengqing wrote:
> Per PCI Firmware Specification Revision 3.3 Table 4-7 _DSM Definitions
> for PCI. Preserve PCI Boot Configuration Initial Revision ID changed to 2.
> But the code remains unchanged, still 1.
> 
> v3:try revision id 1 first, then try revision id 2.
> v2:add Fixes tag.
> 
> Fixes: 9d7d5db8e78e ("PCI: Move PRESERVE_BOOT_CONFIG _DSM evaluation to pci_register_host_bridge()")
> 
> Signed-off-by: Zhou Shengqing <zhoushengqing@...info.com>
> ---
>  drivers/pci/pci-acpi.c | 40 +++++++++++++++++++++++++++++++---------
>  1 file changed, 31 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index af370628e583..ae3b315d708c 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -126,16 +126,38 @@ bool pci_acpi_preserve_config(struct pci_host_bridge *host_bridge)
>  		union acpi_object *obj;
>  
>  		/*
> -		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
> -		 * exists and returns 0, we must preserve any PCI resource
> -		 * assignments made by firmware for this host bridge.
> +		 * Per PCI Firmware r3.2, released Jan 26, 2015,
> +		 * DSM_PCI_PRESERVE_BOOT_CONFIG Revision ID is 1.
> +		 * But PCI Firmware r3.3, released Jan 20, 2021,
> +		 * changed sec 4.6.5 to say
> +		 * "lowest valid Revision ID value: 2". So try revision 1
> +		 * first for old platform, then try revision 2.
>  		 */
> -		obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev),
> -					      &pci_acpi_dsm_guid,
> -					      1, DSM_PCI_PRESERVE_BOOT_CONFIG,
> -					      NULL, ACPI_TYPE_INTEGER);
> -		if (obj && obj->integer.value == 0)
> -			return true;
> +		if (acpi_check_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
> +			    1ULL << DSM_PCI_PRESERVE_BOOT_CONFIG)) {
> +			/*
> +			 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
> +			 * exists and returns 0, we must preserve any PCI resource
> +			 * assignments made by firmware for this host bridge.
> +			 */
> +			obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev),
> +							  &pci_acpi_dsm_guid,
> +						  1, DSM_PCI_PRESERVE_BOOT_CONFIG,
> +						  NULL, ACPI_TYPE_INTEGER);
> +			if (obj && obj->integer.value == 0)
> +				return true;
> +		}
> +
> +		if (acpi_check_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 2,
> +			    1ULL << DSM_PCI_PRESERVE_BOOT_CONFIG)) {
> +			obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev),
> +							  &pci_acpi_dsm_guid,
> +						  2, DSM_PCI_PRESERVE_BOOT_CONFIG,
> +						  NULL, ACPI_TYPE_INTEGER);
> +			if (obj && obj->integer.value == 0)
> +				return true;
> +		}
> +
>  		ACPI_FREE(obj);
>  	}
>  
> -- 
> 2.39.2