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

From: Vidya Sagar
Date: Wed Sep 14 2022 - 07:02:33 EST

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.

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.