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Date:   Fri, 30 Oct 2020 13:25:30 -0600
From:   Alex Williamson <alex.williamson@redhat.com>
To:     Rajat Jain <rajatja@google.com>
Cc:     linux-pci@vger.kernel.org, "Boris V." <borisvk@bstnet.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Bjorn Helgaas <helgaas@kernel.org>, rajatxjain@gmail.com
Subject: Re: [PATCH] PCI: Always call pci_enable_acs() regardless of
 pdev->acs_cap
Message-ID: <20201030132530.59bd8b9a@w520.home>
In-Reply-To: <20201028231545.4116866-1-rajatja@google.com>
References: <20201028231545.4116866-1-rajatja@google.com>
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On Wed, 28 Oct 2020 16:15:45 -0700
Rajat Jain <rajatja@google.com> wrote:

> Some devices may have have anomalies with the ACS cpability structure,
> and they may be using quirks to support ACS functionality via other
> registers. For such devices, it is important we always call
> pci_enable_acs() to give the quirks a chance to enable ACS in other ways.
> 
> For Eg:
> There seems a class of Intel devices quirked with *_intel_pch_acs_*
> functions, that do not expose the standard ACS capability structure. But
> these quirks help support ACS on these devices using other registers:
> pci_quirk_enable_intel_pch_acs() -> doesn't use acs_cap to enable ACS
> 
> This has already been taken care of in the quirks, in the other direction
> i.e. when checking if the ACS is enabled or not. So no need to do
> anything there.
> 
> Reported-by: Boris V <borisvk@bstnet.org>
> Fixes: 52fbf5bdeeef ("PCI: Cache ACS capability offset in device")
> Signed-off-by: Rajat Jain <rajatja@google.com>
> ---
>  drivers/pci/pci.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 6d4d5a2f923d..ab398226c55e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3516,8 +3516,13 @@ void pci_acs_init(struct pci_dev *dev)
>  {
>  	dev->acs_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
>  
> -	if (dev->acs_cap)
> -		pci_enable_acs(dev);
> +	/*
> +	 * Attempt to enable ACS regardless of capability because some rootports
> +	 * (e.g. the ones quirked with *_intel_pch_acs_*) may not expose
> +	 * standard rootport capability structure, but still may support ACS via
> +	 * those quirks.
> +	 */
> +	pci_enable_acs(dev);
>  }
>  
>  /**

Much needed regression fix for v5.9:

Reviewed-by: Alex Williamson <alex.williamson@redhat.com>