linux-kernel - Re: [PATCH v2 1/1] PCI/IOV: Fix incorrect cfg

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Date:   Wed, 12 Jun 2019 11:41:36 -0700
From:   sathyanarayanan kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, ashok.raj@...el.com,
        keith.busch@...el.com, mike.campin@...el.com
Subject: Re: [PATCH v2 1/1] PCI/IOV: Fix incorrect cfg_size for VF > 0


On 6/12/19 11:19 AM, Alex Williamson wrote:
> On Wed, 12 Jun 2019 10:06:47 -0700
> sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
>
>> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>>
>> Commit 975bb8b4dc93 ("PCI/IOV: Use VF0 cached config space size for
>> other VFs") calculates and caches the cfg_size for VF0 device before
>> initializing the pcie_cap of the device which results in using incorrect
>> cfg_size for all VF devices > 0. So set pcie_cap of the device before
>> calculating the cfg_size of VF0 device.
>>
>> Fixes: 975bb8b4dc93 ("PCI/IOV: Use VF0 cached config space size for
>> other VFs")
>> Cc: Ashok Raj <ashok.raj@...el.com>
>> Suggested-by: Mike Campin <mike.campin@...el.com>
>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>> ---
>>
>> Changes since v1:
>>   * Fixed a typo in commit message.
>>
>>   drivers/pci/iov.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>> index 3aa115ed3a65..2869011c0e35 100644
>> --- a/drivers/pci/iov.c
>> +++ b/drivers/pci/iov.c
>> @@ -160,6 +160,7 @@ int pci_iov_add_virtfn(struct pci_dev *dev, int id)
>>   	virtfn->device = iov->vf_device;
>>   	virtfn->is_virtfn = 1;
>>   	virtfn->physfn = pci_dev_get(dev);
>> +	virtfn->pcie_cap = pci_find_capability(virtfn, PCI_CAP_ID_EXP);
>>   
>>   	if (id == 0)
>>   		pci_read_vf_config_common(virtfn);
> Why not re-order until after we've setup pcie_cap?
>
> https://lore.kernel.org/linux-pci/20190604143617.0a226555@x1.home/T/#

pci_read_vf_config_common() also caches values for properties like 
class, hdr_type, susbsystem_vendor/device. These values are read/used in 
pci_setup_device(). So if we can use cached values in 
pci_setup_device(), we don't have to read them from registers twice for 
each device.

>
> Thanks,
> Alex
>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer