linux-kernel - Re: [PATCH v4 3/7] PCI/VPD: Add VPD release quirk for Amazon's Annapurna Labs Root Port

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Date:   Thu, 22 Aug 2019 14:36:24 +0000
From:   "Chocron, Jonathan" <jonnyc@...zon.com>
To:     "andrew.murray@....com" <andrew.murray@....com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "Hanoch, Uri" <hanochu@...zon.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "gustavo.pimentel@...opsys.com" <gustavo.pimentel@...opsys.com>,
        "Wasserstrom, Barak" <barakw@...zon.com>,
        "Saidi, Ali" <alisaidi@...zon.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "Hawa, Hanna" <hhhawa@...zon.com>,
        "Shenhar, Talel" <talel@...zon.com>,
        "Krupnik, Ronen" <ronenk@...zon.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "Chocron, Jonathan" <jonnyc@...zon.com>
Subject: Re: [PATCH v4 3/7] PCI/VPD: Add VPD release quirk for Amazon's
 Annapurna Labs Root Port

On Thu, 2019-08-22 at 12:41 +0100, Andrew Murray wrote:
> On Wed, Aug 21, 2019 at 06:35:43PM +0300, Jonathan Chocron wrote:
> > The Amazon Annapurna Labs PCIe Root Port exposes the VPD
> > capability,
> > but there is no actual support for it.
> > 
> > The reason for not using the already existing quirk_blacklist_vpd()
> > is that, although this fails pci_vpd_read/write, the 'vpd' sysfs
> > entry still exists. When running lspci -vv, for example, this
> > results in the following error:
> > 
> > pcilib: sysfs_read_vpd: read failed: Input/output error
> 
> Oh that's not nice. It's probably triggered by the -EIO in
> pci_vpd_read.
> A quick search online seems to show that other people have
> experienced
> this too - though from as far as I can tell this just gives you a
> warning and pcilib will continnue to give other output?
> 
Correct.

> I guess every vpd blacklist'd driver will have the same issue. And
> for
> this reason I don't think that this patch is the right solution - as
> otherwise all the other blacklisted drivers could follow your lead.
> 
I think that going forward, they should follow my lead, I just didn't
want to possibly break any assumptions other vendors' tools might have
regarding the existence/non-existence of the vpd sysfs entry.

> I don't think you need to fix this specifically for the AL driver and
> so
> I'd suggest that you can probably drop this patch. (Ideally pciutils
> could be updated to not warn for this specific use-case).
> 
I don't think that solution should be implemented in pcituils. It
rightfully warns when it fails to read from the vpd sysfs file - it
first 'open's the file which succeeds, and then fails when trying to
'read' from it. I don't think that it should specifically "mask" out
-EIO, since it shouldn't have to "know" that the underlying reason is a
VPD quirk (or more precisely vpd->len == 0). Furthermore, it is
possible that this error code would be returned for some other reason
(not sure if currently this occurs).

I think that if the device doesn't properly support vpd, the kernel
shouldn't expose the "empty" sysfs file in the first place.

In the long run, quirk_blacklist_vpd() should probably be modified to
do what our quirk does or something similar (and then the al quirk can
be removed). What do you think?

> Thanks,
> 
> Andrew Murray
> 
> > 
> > This quirk removes the sysfs entry, which avoids the error print.
> > 
> > Signed-off-by: Jonathan Chocron <jonnyc@...zon.com>
> > Reviewed-by: Gustavo Pimentel <gustavo.pimentel@...opsys.com>
> > ---
> >  drivers/pci/vpd.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> > 
> > diff --git a/drivers/pci/vpd.c b/drivers/pci/vpd.c
> > index 4963c2e2bd4c..c23a8ec08db9 100644
> > --- a/drivers/pci/vpd.c
> > +++ b/drivers/pci/vpd.c
> > @@ -644,4 +644,20 @@ static void quirk_chelsio_extend_vpd(struct
> > pci_dev *dev)
> >  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_CHELSIO, PCI_ANY_ID,
> >  			quirk_chelsio_extend_vpd);
> >  
> > +static void quirk_al_vpd_release(struct pci_dev *dev)
> > +{
> > +	if (dev->vpd) {
> > +		pci_vpd_release(dev);
> > +		dev->vpd = NULL;
> > +		pci_warn(dev, FW_BUG "Releasing VPD capability (No
> > support for VPD read/write transactions)\n");
> > +	}
> > +}
> > +
> > +/*
> > + * The 0031 device id is reused for other non Root Port device
> > types,
> > + * therefore the quirk is registered for the PCI_CLASS_BRIDGE_PCI
> > class.
> > + */
> > +DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_AMAZON_ANNAPURNA_LABS,
> > 0x0031,
> > +			      PCI_CLASS_BRIDGE_PCI, 8,
> > quirk_al_vpd_release);
> > +
> >  #endif
> > -- 
> > 2.17.1
> >