Re: [PATCH v3 1/7] PCI/ATS: Fix pci_prg_resp_pasid_required() dependency issues

[sathyanarayanan kuppuswamy]

Hi,

On 7/3/19 10:56 AM, Bjorn Helgaas wrote:
> On Thu, Jun 20, 2019 at 01:38:42PM -0700, sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx wrote:
> > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> >
> > 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.
> This is likely just confusion on my part, but I don't understand what
> you're doing here.
>
> pci_prg_resp_pasid_required() does not actually *depend* on the
> CONFIG_PCI_PRI config symbol.

pci_prg_resp_pasid_required() function internally reads the PRI status 
register to get the status of PASID required bit.

FILE:drivers/pci/ats.c

419ÂÂÂÂÂÂÂÂ pci_read_config_word(pdev, pos + PCI_PRI_STATUS, &status);
420
421ÂÂÂÂÂÂÂÂ if (status & PCI_PRI_STATUS_PASID)

Since pci_prg_resp_pasid_required()Â function is only used if 
CONFIG_PCI_PASID is enabled, and since it also has internal PCI_PRI 
dependency, I have protected it with both CONFIG_PCI_PASID and 
CONFIG_PCI_PRI ifdefs.

> It is currently compiled only if CONFIG_PCI_ATS=y (which controls
> compilation of the entire ats.c) and CONFIG_PCI_PASID=y (since it's
> within #ifdef CONFIG_PCI_PASID).
>
> pci_prg_resp_pasid_required() is called by attach_device()
> (amd_iommu.c), which is only compiled if CONFIG_AMD_IOMMU=y, and that
> selects PCI_PRI.
pci_prg_resp_pasid_required() is also called by intel_iommu.c, and 
enabling CONFIG_INTEL_IOMMU does not enable PCI_PRI/PCI_PASID by default.
> It is also called by iommu_enable_dev_iotlb() (intel-iommu.c).  That
> file is compiled if CONFIG_INTEL_IOMMU=y and the call itself is inside
> #ifdef CONFIG_INTEL_IOMMU_SVM.  But I don't see the PCI_PRI connection
> here.
>
> If this is just to limit the visibility, say that.  But I don't think
> that's really a good reason.  The chain of config symbols seems a
> little too complicated.
>
> > Fixes: e5567f5f6762 ("PCI/ATS: Add pci_prg_resp_pasid_required()
> > interface.")
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > ---
> >   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 97c08146534a..f9eeb7db0db3 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