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

On 7/3/19 10:56 AM, Bjorn Helgaas wrote:
> On Thu, Jun 20, 2019 at 01:38:42PM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
>> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.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.
> 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

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

Since pci_prg_resp_pasid_required()  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@linux.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 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

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