linux-kernel - Re: [PATCH 1/2] PCI/IOV: Add function to allow Function Dependency Link override.

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Message-ID: <57BB10E5.1050506@caviumnetworks.com>
Date:   Mon, 22 Aug 2016 07:49:09 -0700
From:   David Daney <ddaney@...iumnetworks.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     Omer Khaliq <okhaliq@...iumnetworks.com>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-crypto@...r.kernel.org>, <linux-arm-kernel@...r.kernel.org>,
        <bhelgaas@...gle.com>, <mpm@...enic.com>,
        <herbert@...dor.apana.org.au>, <Ananth.Jasty@...ium.com>,
        <david.daney@...ium.com>
Subject: Re: [PATCH 1/2] PCI/IOV: Add function to allow Function Dependency
 Link override.

On 08/22/2016 07:36 AM, Bjorn Helgaas wrote:
> Hi David & Omer,
>
> On Fri, Aug 19, 2016 at 03:32:12PM -0700, Omer Khaliq wrote:
>> From: David Daney <david.daney@...ium.com>
>>
>> Some hardware presents an incorrect SR-IOV Function Dependency Link,
>> add a function to allow this to be overridden in the PF driver for
>> such devices.
>>
>> Signed-off-by: David Daney <david.daney@...ium.com>
>> Signed-off-by: Omer Khaliq <okhaliq@...iumnetworks.com>
>> ---
>>   drivers/pci/iov.c   | 14 ++++++++++++++
>>   include/linux/pci.h |  1 +
>>   2 files changed, 15 insertions(+)
>>
>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>> index 2194b44..81f0672 100644
>> --- a/drivers/pci/iov.c
>> +++ b/drivers/pci/iov.c
>> @@ -640,6 +640,20 @@ int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn)
>>   EXPORT_SYMBOL_GPL(pci_enable_sriov);
>>
>>   /**
>> + * pci_sriov_fdl_override - fix incorrect Function Dependency Link
>> + * @dev: the PCI device
>> + * @fdl: the corrected Function Dependency Link value
>> + *
>> + * For hardware presenting an incorrect Function Dependency Link in
>> + * the SR-IOV Extended Capability, allow a driver to override it.
>> + */
>> +void pci_sriov_fdl_override(struct pci_dev *dev, u8 fdl)
>> +{
>> +	dev->sriov->link = fdl;
>> +}
>> +EXPORT_SYMBOL_GPL(pci_sriov_fdl_override);
>
> We usually use quirks to work around problems in config space.  That's
> a nice mechanism because we don't have to add new PCI core interfaces
> and it makes it clear that we're working around a hardware problem.
>
> Can you use a quirk here?  We allocate dev->sriov in the
> pci_init_capabilities() path, so it looks like a pci_fixup_final quirk
> should work.
>

The struct pci_sriov definition is private to drivers/pci, so in order 
to use a quirk to fix this, we would have to put it in 
drivers/pci/quirks.c.  I was trying to keep this very device specific 
code in the driver, which requires an accessor to be able to manipulate 
the dev->sriov->link field.

If you prefer a quirk in drivers/pci/quirks.c, we can certainly do that 
instead.

Thanks for taking the time to look at this,
David Daney




>> +
>> +/**
>>    * pci_disable_sriov - disable the SR-IOV capability
>>    * @dev: the PCI device
>>    */
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 2599a98..da8a5b3 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -1823,6 +1823,7 @@ int pci_num_vf(struct pci_dev *dev);
>>   int pci_vfs_assigned(struct pci_dev *dev);
>>   int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs);
>>   int pci_sriov_get_totalvfs(struct pci_dev *dev);
>> +void pci_sriov_fdl_override(struct pci_dev *dev, u8 fdl);
>>   resource_size_t pci_iov_resource_size(struct pci_dev *dev, int resno);
>>   #else
>>   static inline int pci_iov_virtfn_bus(struct pci_dev *dev, int id)
>> --
>> 1.9.1
>>
>> --
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