Re: [PATCH] PCI: Add CRS timeout for pci_device_is_present()

[Vidya Sagar <vidyas@nvidia.com>]

On 10/21/2019 11:13 AM, Vidya Sagar wrote:

Hi Sinan / Rafael,
Apologies for the ping again.
Do you guys have any further comments on this?

-Vidya Sagar

> On 10/15/2019 5:44 PM, Vidya Sagar wrote:
> 
> Hi Sinan / Rafael,
> Do you have any further comments on this patch?
> 
> - Vidya Sagar
> 
>> On 10/15/2019 4:40 PM, Sinan Kaya wrote:
>>> +Rafael
>>>
>>> On 10/15/2019 2:30 AM, Thierry Reding wrote:
>>>> Vidya, can you clarify for which device you're seeing the issues? Sounds
>>>> like adding a call to pci_pm_reset() (via pci_reset_function()) at some
>>>> point.
>>>>
>>>> Sinan, it looks as if pci_pm_reset() (or any of its callers) is not used
>>>> very widely. Is that just because most drivers haven't had a need for it
>>>> yet? Or am I missing some core functionality that calls this for every
>>>> device anyway?
>>>
>>> pci_pm_reset() is there as an alternative reset path. We are not
>>> supposed to call this function. Sorry for giving you wrong direction
>>> here. pci_reset_function() should call it only if there is no other
>>> suitable reset function is found.
>>>
>>> I think the PCI core should be putting the device back D0 state as one
>>> of the first actions before enumerating. Wake up could be a combination
>>> of ACPI and/or PCI wake up depending on where your device sits in the
>>> topology.
>> Yup. It is indeed doing it as part of pci_power_up() in pci.c file.
>> But, what is confusing to me is the order of the calls.
>> pci_power_up() has following calls in the same order.
>>      pci_raw_set_power_state(dev, PCI_D0);
>>      pci_update_current_state(dev, PCI_D0);
>> But, pci_raw_set_power_state() is accessing config space without calling
>> pci_device_is_present() whereas pci_update_current_state() which is called
>> later in the flow is calling pci_device_is_present()...!
>>
>>>
>>> On the other hand, wake up code doesn't perform the CRS wait. CRS
>>> wait is deferred until the first vendor id read in pci_scan_device().
>>> I see that it already waits for 60 seconds.
>>>
>>> Going back to the patch...
>>>
>>> I think we need to find the path that actually needs this sleep and
>>> put pci_dev_wait() there.
>> Following is the path in resume() flow.
>> [   36.380726] Call trace:
>> [   36.383270]  dump_backtrace+0x0/0x158
>> [   36.386802]  show_stack+0x14/0x20
>> [   36.389749]  dump_stack+0xb0/0xf8
>> [   36.393451]  pci_update_current_state+0x58/0xe0
>> [   36.398178]  pci_power_up+0x60/0x70
>> [   36.401672]  pci_pm_resume_noirq+0x6c/0x130
>> [   36.405669]  dpm_run_callback.isra.16+0x20/0x70
>> [   36.410248]  device_resume_noirq+0x120/0x238
>> [   36.414364]  async_resume_noirq+0x24/0x58
>> [   36.418364]  async_run_entry_fn+0x40/0x148
>> [   36.422418]  process_one_work+0x1e8/0x360
>> [   36.426525]  worker_thread+0x40/0x488
>> [   36.430201]  kthread+0x118/0x120
>> [   36.433843]  ret_from_fork+0x10/0x1c
>>
>>>
>>> +++ b/drivers/pci/pci.c
>>> @@ -5905,7 +5905,8 @@ bool pci_device_is_present(struct pci_dev *pdev)
>>>
>>>       if (pci_dev_is_disconnected(pdev))
>>>           return false;
>>> -    return pci_bus_read_dev_vendor_id(pdev->bus, pdev->devfn, &v, 0);
>>> +    return pci_bus_read_dev_vendor_id(pdev->bus, pdev->devfn, &v,
>>> +                      PCI_CRS_TIMEOUT);
>>>   }
>>>
>>> pci_device_is_present() is a too low-level function and it may not
>>> be allowed to sleep. It uses 0 as timeout value.
>>>
>>>
>>
>