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

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Date:   Fri, 16 Aug 2019 11:06:38 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
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 10:51:48PM -0500, Bjorn Helgaas wrote:
> 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.
Its not only pri_lock. This function also uses "pri_cap" which is also
only defined for CONFIG_PCI_PRI. "pri_cap" is added by next patch in the
series which adds caching support for PRI capability check. So this
patch is still required even if we remove use of pri_lock in this
function.
> 
> > > > 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
> > 

-- 
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer