linux-kernel - Re: [PATCH v9 7/8] PCI/DPC: Clear AER registers in EDR mode

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Message-ID: <c68a0725-0e31-d140-eea9-5aa43d07b861@linux.intel.com>
Date:   Tue, 29 Oct 2019 16:37:47 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...el.com, keith.busch@...el.com
Subject: Re: [PATCH v9 7/8] PCI/DPC: Clear AER registers in EDR mode


On 10/29/19 3:48 PM, Bjorn Helgaas wrote:
> On Tue, Oct 29, 2019 at 01:04:29PM -0700, Kuppuswamy Sathyanarayanan wrote:
>> On 10/28/19 4:27 PM, Bjorn Helgaas wrote:
>>> On Thu, Oct 03, 2019 at 04:39:03PM -0700, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
>>>> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>>>>
>>>> As per PCI firmware specification r3.2 Downstream Port Containment
>>>> Related Enhancements ECN,
>>> Specific reference, please, e.g., the section/table/figure of the PCI
>>> Firmware Spec being modified by the ECN.
>> Ok. I will include it.
>>>> OS is responsible for clearing the AER
>>>> registers in EDR mode. So clear AER registers in dpc_process_error()
>>>> function.
>>>>
>>>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>>>> Acked-by: Keith Busch <keith.busch@...el.com>
>>>> ---
>>>>    drivers/pci/pcie/dpc.c | 4 ++++
>>>>    1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
>>>> index fafc55c00fe0..de2d892bc7c4 100644
>>>> --- a/drivers/pci/pcie/dpc.c
>>>> +++ b/drivers/pci/pcie/dpc.c
>>>> @@ -275,6 +275,10 @@ static void dpc_process_error(struct dpc_dev *dpc)
>>>>    		pci_aer_clear_fatal_status(pdev);
>>>>    	}
>>>> +	/* In EDR mode, OS is responsible for clearing AER registers */
>>>> +	if (dpc->firmware_dpc)
>>> I guess "EDR mode" is effectively the same as "firmware-first mode"?
>> Yes, EDR mode is an upgrade to FF mode in which firmware allows OS
>> to share some of it job by sending ACPI notification. If you don't
>> get ACPI notification, EDR mode is effectively same as FF mode.
May be I can add some documentation in code to explain the EDR mode better.
> Hmm, somehow the connection between FF and EDR needs to be clear from
> the code, so people who weren't involved in the development of EDR and
> don't even have access to the specs/ECNs can make sense out of this.
>
>>> At least, the only place we set "firmware_dpc = 1" is:
>>>
>>>     +       if (pcie_aer_get_firmware_first(pdev))
>>>     +               dpc->firmware_dpc = 1;
>>>
>>> If they're the same, why do we need two different names for it?
>> For better readability and performance, I tried to cache the value of
>> pcie_aer_get_firmware_first() result in DPC driver.
> pcie_aer_get_firmware_first() already caches the value, so I don't
> think you're gaining any useful performance here, and having two
> different names *decreases* readability.
Ok. I can replace "firmware_dpc" with pcie_aer_get_firmware_first() calls.
>
> I do agree that pcie_aer_get_firmware_first() is not optimally
> implemented.  I think we should probably look up the firmware-first
> indication explicitly during enumeration so we don't have to bother
> with the dev->__aer_firmware_first_valid thing.  And if we got rid of
> all those leading underscores, it would probably run faster, too ;)
I agree that pcie_aer_get_firmware_first() can be optimized. I can submit a
patch for it once this patch set is merged.
>
>>>> +		pci_cleanup_aer_error_status_regs(pdev);
>>>> +
>>>>    	/*
>>>>    	 * Irrespective of whether the DPC event is triggered by
>>>>    	 * ERR_FATAL or ERR_NONFATAL, since the link is already down,
>>>> -- 
>>>> 2.21.0
>>>>
>> -- 
>> Sathyanarayanan Kuppuswamy
>> Linux kernel developer
>>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer