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 12:52:48 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
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 14/09/2022 12:43, Manivannan Sadhasivam wrote:
> 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.

Correct it is exposed via a standard connector. Yes for PCIe slots that 
are not connected to an on-board device or connector, in that case it 
would make sense to disable, but this is not the case here.

Jon

-- 
nvpublic