linux-kernel - Re: [PATCH V1] PCI: dwc: Use dev_info for PCIe link down event logging

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Message-ID: <75b9bbc0-0e99-3201-f83d-f1fe28c54b12@nvidia.com>
Date:   Mon, 26 Sep 2022 15:59:29 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Rob Herring <robh@...nel.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Jon Hunter <jonathanh@...dia.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczynski <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thierry Reding <treding@...dia.com>,
        PCI <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Krishna Thota <kthota@...dia.com>,
        Manikanta Maddireddy <mmaddireddy@...dia.com>,
        sagar.tv@...il.com
Subject: Re: [PATCH V1] PCI: dwc: Use dev_info for PCIe link down event
 logging

Hi,
Just checking if we are good with this patch or does it need any further 
modifications?

Thanks,
Vidya Sagar

On 9/15/2022 8:22 PM, Manivannan Sadhasivam wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Thu, Sep 15, 2022 at 09:16:27AM -0500, Rob Herring wrote:
>> On Wed, Sep 14, 2022 at 1:24 AM Manivannan Sadhasivam
>> <manivannan.sadhasivam@...aro.org> wrote:
>>>
>>> On Tue, Sep 13, 2022 at 03:07:46PM -0500, Bjorn Helgaas wrote:
>>>> On Tue, Sep 13, 2022 at 06:00:30PM +0100, Jon Hunter wrote:
>>>>> On 13/09/2022 17:51, Manivannan Sadhasivam wrote:
>>>>>> On Tue, Sep 13, 2022 at 03:42:37PM +0530, Vidya Sagar wrote:
>>>>>>> Some of the platforms (like Tegra194 and Tegra234) have open slots and
>>>>>>> not having an endpoint connected to the slot is not an error.
>>>>>>> So, changing the macro from dev_err to dev_info to log the event.
>>>>>>
>>>>>> But the link up not happening is an actual error and -ETIMEDOUT is being
>>>>>> returned. So I don't think the log severity should be changed.
>>>>>
>>>>> Yes it is an error in the sense it is a timeout, but reporting an error
>>>>> because nothing is attached to a PCI slot seems a bit noisy. Please note
>>>>> that a similar change was made by the following commit and it also seems
>>>>> appropriate here ...
>>>>>
>>>>> commit 4b16a8227907118e011fb396022da671a52b2272
>>>>> Author: Manikanta Maddireddy <mmaddireddy@...dia.com>
>>>>> Date:   Tue Jun 18 23:32:06 2019 +0530
>>>>>
>>>>>      PCI: tegra: Change link retry log level to debug
>>>>>
>>>>>
>>>>> BTW, we check for error messages in the dmesg output and this is a new error
>>>>> seen as of Linux v6.0 and so this was flagged in a test. We can ignore the
>>>>> error, but in this case it seem more appropriate to make this a info or
>>>>> debug level print.
>>>>
>>>> Can you tell whether there's a device present, e.g., via Slot Status
>>>> Presence Detect?  If there's nothing in the slot, I don't know why we
>>>> would print anything at all.  If a card is present but there's no
>>>> link, that's probably worthy of dev_info() or even dev_err().
>>>>
>>>
>>> I don't think all form factors allow for the PRSNT pin to be wired up,
>>> so we cannot know if the device is actually present in the slot or not all
>>> the time. Maybe we should do if the form factor supports it?
>>>
>>>> I guess if you can tell the slot is empty, there's no point in even
>>>> trying to start the link, so you could avoid both the message and the
>>>> timeout by not even calling dw_pcie_wait_for_link().
>>>
>>> Right. There is an overhead of waiting for ~1ms during boot.
>>
>> Async probe should mitigate that, right? Saravana is working toward
>> making that the default instead of opt in, but you could opt in now.
>>
> 
> No. The delay is due to the DWC core waiting for link up that depends on
> the PCIe device to be present on the slot. The driver probe order
> doesn't apply here.
> 
> Thanks,
> Mani
> 
>> Rob