linux-kernel - Re: [PATCH v7 1/7] PCI/ATS: Fix pci_prg_resp_pasid

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Date:   Thu, 3 Oct 2019 14:04:13 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...el.com, keith.busch@...el.com
Subject: Re: [PATCH v7 1/7] PCI/ATS: Fix pci_prg_resp_pasid_required()
 dependency issues

On Thu, Oct 03, 2019 at 10:20:24AM -0700, Kuppuswamy Sathyanarayanan wrote:
> Hi Bjorn,
> 
> Thanks for looking into this patch set.
> 
> On 9/5/19 12:18 PM, Bjorn Helgaas wrote:
> > On Wed, Aug 28, 2019 at 03:14:01PM -0700, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> > > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > > 
> > > Since pci_prg_resp_pasid_required() function has dependency on both
> > > PASID and PRI, define it only if both CONFIG_PCI_PRI and
> > > CONFIG_PCI_PASID config options are enabled.
> > > 
> > > Fixes: e5567f5f6762 ("PCI/ATS: Add pci_prg_resp_pasid_required()
> > > interface.")
> > [Don't split tags, including "Fixes:" across lines]
> > 
> > This definitely doesn't fix e5567f5f6762.  That commit added
> > pci_prg_resp_pasid_required(), but with no dependency on
> > CONFIG_PCI_PRI or CONFIG_PCI_PASID.
> > 
> > This patch is only required when a subsequent patch is applied.  It
> > should be squashed into the commit that requires it so it's obvious
> > why it's needed.
> > 
> > I've been poking at this series, and I'll post a v8 soon with this and
> > other fixes.
> In your v8 submission you did not merge this patch. You did not use
> pri_cap or pasid_cap cached values. Instead you have re-read the
> value from register. Is this intentional?
> 
> Since this function will be called for every VF device we might loose some
> performance benefit.

This particular patch doesn't do any caching.  IIRC it fiddles with
ifdefs to solve a problem that would be introduced by a future patch.
I don't remember the exact details, but I think the series I merged
doesn't have that problem.  If it does, let me know the details and we
can fix it.

I did include the caching patches for both PRI and PASID capabilities,
but they're only performance optimizations so I moved them to the end
so the functional fixes would be smaller and earlier in the series.

> > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > > ---
> > >   drivers/pci/ats.c       | 10 ++++++----
> > >   include/linux/pci-ats.h | 12 +++++++++---
> > >   2 files changed, 15 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> > > index e18499243f84..cdd936d10f68 100644
> > > --- a/drivers/pci/ats.c
> > > +++ b/drivers/pci/ats.c
> > > @@ -395,6 +395,8 @@ int pci_pasid_features(struct pci_dev *pdev)
> > >   }
> > >   EXPORT_SYMBOL_GPL(pci_pasid_features);
> > > +#ifdef CONFIG_PCI_PRI
> > > +
> > >   /**
> > >    * pci_prg_resp_pasid_required - Return PRG Response PASID Required bit
> > >    *				 status.
> > > @@ -402,10 +404,8 @@ EXPORT_SYMBOL_GPL(pci_pasid_features);
> > >    *
> > >    * Returns 1 if PASID is required in PRG Response Message, 0 otherwise.
> > >    *
> > > - * Even though the PRG response PASID status is read from PRI Status
> > > - * Register, since this API will mainly be used by PASID users, this
> > > - * function is defined within #ifdef CONFIG_PCI_PASID instead of
> > > - * CONFIG_PCI_PRI.
> > > + * Since this API has dependency on both PRI and PASID, protect it
> > > + * with both CONFIG_PCI_PRI and CONFIG_PCI_PASID.
> > >    */
> > >   int pci_prg_resp_pasid_required(struct pci_dev *pdev)
> > >   {
> > > @@ -425,6 +425,8 @@ int pci_prg_resp_pasid_required(struct pci_dev *pdev)
> > >   }
> > >   EXPORT_SYMBOL_GPL(pci_prg_resp_pasid_required);
> > > +#endif
> > > +
> > >   #define PASID_NUMBER_SHIFT	8
> > >   #define PASID_NUMBER_MASK	(0x1f << PASID_NUMBER_SHIFT)
> > >   /**
> > > diff --git a/include/linux/pci-ats.h b/include/linux/pci-ats.h
> > > index 1ebb88e7c184..1a0bdaee2f32 100644
> > > --- a/include/linux/pci-ats.h
> > > +++ b/include/linux/pci-ats.h
> > > @@ -40,7 +40,6 @@ void pci_disable_pasid(struct pci_dev *pdev);
> > >   void pci_restore_pasid_state(struct pci_dev *pdev);
> > >   int pci_pasid_features(struct pci_dev *pdev);
> > >   int pci_max_pasids(struct pci_dev *pdev);
> > > -int pci_prg_resp_pasid_required(struct pci_dev *pdev);
> > >   #else  /* CONFIG_PCI_PASID */
> > > @@ -67,11 +66,18 @@ static inline int pci_max_pasids(struct pci_dev *pdev)
> > >   	return -EINVAL;
> > >   }
> > > +#endif /* CONFIG_PCI_PASID */
> > > +
> > > +#if defined(CONFIG_PCI_PRI) && defined(CONFIG_PCI_PASID)
> > > +
> > > +int pci_prg_resp_pasid_required(struct pci_dev *pdev);
> > > +
> > > +#else /* CONFIG_PCI_PASID && CONFIG_PCI_PRI */
> > > +
> > >   static inline int pci_prg_resp_pasid_required(struct pci_dev *pdev)
> > >   {
> > >   	return 0;
> > >   }
> > > -#endif /* CONFIG_PCI_PASID */
> > > -
> > > +#endif
> > >   #endif /* LINUX_PCI_ATS_H*/
> > > -- 
> > > 2.21.0
> > > 
> -- 
> Sathyanarayanan Kuppuswamy
> Linux kernel developer
>