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

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Message-ID: <20221027110316.GA76627@thinkpad>
Date:   Thu, 27 Oct 2022 16:33:16 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Lorenzo Pieralisi <lpieralisi@...nel.org>
Cc:     Rob Herring <robh@...nel.org>, Bjorn Helgaas <helgaas@...nel.org>,
        Jon Hunter <jonathanh@...dia.com>,
        Vidya Sagar <vidyas@...dia.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        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

On Thu, Oct 27, 2022 at 11:39:02AM +0200, Lorenzo Pieralisi wrote:
> 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.
> 
> I read this as "trying to bring the link up is mandatory because
> we can't detect an empty slot, therefore ~1ms delay during boot
> is unavoidable" and on that Rob's suggestion applies.
> 

Right. Rob's suggestion came as areply to my worry on waiting for link up
during boot.

> Just to understand where this thread is going. The suggestion
> above does not change the aim of this patch, that seems reasonable
> to me and it makes sense even if/when what Rob is suggesting is
> implemented.
> 
> Is that correct ?
> 

Yes, Rob's suggestion makes sense to me. And it has to be implemented as a
separate patch but this patch itself is required to demote the error log to
debug.

Thanks,
Mani

> Thanks,
> Lorenzo

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