linux-kernel - Re: [PATCH V1 0/4] GPIO based PCIe Hot-Plug support

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Date:   Mon, 10 Oct 2022 11:44:29 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>, lpieralisi@...nel.org,
        Pali Rohár <pali@...nel.org>,
        Jonathan Derrick <jonathan.derrick@...ux.dev>
Cc:     Lukas Wunner <lukas@...ner.de>, bhelgaas@...gle.com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        kw@...ux.com, thierry.reding@...il.com, jonathanh@...dia.com,
        mani@...nel.org, Sergey.Semin@...kalelectronics.ru,
        jszhang@...nel.org, linux-pci@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, kthota@...dia.com,
        mmaddireddy@...dia.com, sagar.tv@...il.com,
        Marek Behún <kabel@...nel.org>
Subject: Re: [PATCH V1 0/4] GPIO based PCIe Hot-Plug support



On 10/4/2022 9:34 AM, Vidya Sagar wrote:
> 
> 
> On 10/3/2022 11:51 PM, Pali Rohár wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> On Monday 03 October 2022 13:09:49 Bjorn Helgaas wrote:
>>> On Sat, Oct 01, 2022 at 05:50:07PM -0600, Jonathan Derrick wrote:
>>>> On 10/1/2022 10:20 AM, Pali Rohár wrote:
>>>> ...
>>>
>>>>> Would not it better to rather synthesise PCIe Slot Capabilities 
>>>>> support
>>>>> in your PCIe Root Port device (e.g. via pci-bridge-emul.c) and then 
>>>>> let
>>>>> existing PCI hotplug code to take care for hotplugging? Because it
>>>>> already implements all required stuff for re-scanning, registering and
>>>>> unregistering PCIe devices for Root Ports with Slot Capabilities. 
>>>>> And I
>>>>> think that there is no need to have just another (GPIO based)
>>>>> implementation of PCI hotplug.
>>>>
>>>> I did that a few years ago (rejected), but can attest to the 
>>>> robustness of
>>>> the pcie hotplug code on non-hotplug slots.
>>>> https://lwn.net/Articles/811988/
>>>
>>> I think the thread is here:
>>> https://lore.kernel.org/linux-pci/1581120007-5280-1-git-send-email-jonathan.derrick@intel.com/ 
>>>
>>> and I'm sorry that my response came across as "rejected".  I intended
>>> it as "this is good ideas and good work and we should keep going".
>>>
>>> Bjorn
>>
>> Nice! So we have consensus that this is a good idea. Anyway, if you need
>> help with designing something here, please let me know as I have good
>> understanding of all (just two) consumers of pci-bridge-emul.c driver.
>>
> 
> Thanks all for your comments.
> 
> I would like to hear from Bjorn / Lorenzo if the design of the current 
> patch series is fine at a high level or I should explore emulating the 
> root port's configuration space to fake slot config/control registers 
> (which in turn depend on the hotplug GPIO interrupt & state to update 
> Presence Detect related bits in Slot status register) and use the PCIe 
> native Hot-plug framework itself to carry out with enabling the Hot-plug 
> functionality?

Bjorn / Lorenzo,
Could you please take time to comment on the discussion happened here 
and the right approach to be followed?

Thanks,
Vidya Sagar

> 
> Thanks,
> Vidya Sagar
> 
>