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

[Vidya Sagar]

Agree with Mani.
Not all form factors support PRSNT pin (Ex:- M.2 Key-M form factor) and 
even if the slot form factor supports PRSNT, it is not mandatory to have 
a GPIO routed to the PRSNT pin of the slot.
Also, since these are development platforms, we wouldn't want to keep 
changing a controller's status in the DT, instead want to know the 
device's presence/absence (by way of link up) looking at the log.
In my honest opinion, I don't think the absence of a device in the slot 
should be treated as an error.

Thanks,
Vidya Sagar

On 9/14/2022 11:54 AM, Manivannan Sadhasivam wrote:
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> 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@xxxxxxxxxx>
> > > 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.
>
> We workaround this issue by disabling the PCIe instances in devicetree
> for which there would be no devices connected.
>
> Thanks,
> Mani
>
> > Bjorn