linux-kernel - Re: [PATCH v5 1/7] PCI/ATS: Fix pci_prg_resp_pasid

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Date:   Mon, 12 Aug 2019 22:51:48 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     sathyanarayanan kuppuswamy 
        <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 v5 1/7] PCI/ATS: Fix pci_prg_resp_pasid_required()
 dependency issues

On Mon, Aug 12, 2019 at 01:20:55PM -0700, sathyanarayanan kuppuswamy wrote:
> On 8/12/19 1:04 PM, Bjorn Helgaas wrote:
> > On Thu, Aug 01, 2019 at 05:05:58PM -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.

> > I don't really like this.  It makes the #ifdefs more complicated and I
> > don't think it really buys us anything.  Will anything break if we
> > just drop this patch?

> Yes, this function uses "pri_lock" mutex which is only defined if
> CONFIG_PCI_PRI is enabled. So not protecting this function within
> CONFIG_PCI_PRI will lead to compilation issues.

Ah, OK.  That helps a lot.  "pri_lock" doesn't exist at this point in
the series, so the patch makes no sense without knowing that.

I'm still not convinced this is the right thing because I'm not sure
the lock is necessary.  I'll respond to the patch that adds the lock.

> > > Fixes: e5567f5f6762 ("PCI/ATS: Add pci_prg_resp_pasid_required()
> > > interface.")
> > > 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
>