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

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Date:   Wed, 14 Sep 2022 17:13:06 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Vidya Sagar <vidyas@...dia.com>,
        Bjorn Helgaas <helgaas@...nel.org>, jingoohan1@...il.com,
        gustavo.pimentel@...opsys.com, lpieralisi@...nel.org,
        robh@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
        treding@...dia.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, kthota@...dia.com,
        mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V1] PCI: dwc: Use dev_info for PCIe link down event
 logging

On Wed, Sep 14, 2022 at 12:25:51PM +0100, Jon Hunter wrote:
> 
> On 14/09/2022 12:18, Manivannan Sadhasivam wrote:
> > On Wed, Sep 14, 2022 at 04:32:10PM +0530, Vidya Sagar wrote:
> > > 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.
> > 
> > Right.
> > 
> > > 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.
> > > 
> > 
> > As I mentioned earlier, timeout can happen due to an issue with PHY layer
> > also. In those cases, "dev_err()" is relevant.
> > 
> > And I also agree that absence of the device should not be treated as an
> > error. But my question is, if you know that the slot is going to be
> > empty always, why cannot you just disable it in dts?
> 
> I really don't think that makes sense from a usability perspective. You want
> to allow users to connect PCI cards and for them to work without having to
> update the DTB. I have plenty of open PCI slots on my PC and I would be a
> bit upset if someone told me I need to update the PC firmware each time I
> wanted to use a new slot.
> 

My question was, "do you think the slot is going to be empty always".
This can happen with slots exposed through a connector (not a PCIe one) and
users would plug in add-on cards for accessing the slots. In those
cases, the add-on specific devicetree can enable the PCIe instance and
use it.

But from your reply, I can infer that the slot is exposed on a standard
PCIe connector and users would connect a PCIe device any time.

Anyway, I don't strongly object the change and leave it to the
maintainers to decide.

Thanks,
Mani

> Jon
> 
> -- 
> nvpublic