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

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Date:   Mon, 17 Oct 2022 08:16:06 +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 10/10/2022 11:44 AM, Vidya Sagar wrote:
> 
> 
> 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?

I'm really sorry to bug you on this, but would like to hear your 
comments on the approach to be taken. So, I would really like to hear 
your take on this.

Thanks,
Vidya Sagar

> 
> Thanks,
> Vidya Sagar
> 
>>
>> Thanks,
>> Vidya Sagar
>>
>>