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
Date: Fri, 30 Oct 2020 13:25:30 -0600 [thread overview]
Message-ID: <20201030132530.59bd8b9a@w520.home> (raw)
In-Reply-To: <20201028231545.4116866-1-rajatja@google.com>
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>
next prev parent reply other threads:[~2020-10-30 19:26 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 23:15 [PATCH] PCI: Always call pci_enable_acs() regardless of pdev->acs_cap Rajat Jain
2020-10-28 23:19 ` Rajat Jain
2020-10-30 19:25 ` Alex Williamson [this message]
2020-10-30 21:42 ` Bjorn Helgaas
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