Re: [PATCH V3] PCI: tegra: Enable Relaxed Ordering only for Tegra20 & Tegra30

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Hi Lorenzo,

On 09/07/2019 12:02, Jon Hunter wrote:
> On 05/07/2019 10:38, Lorenzo Pieralisi wrote:
>> [+Greg]
>>
>> On Fri, Jul 05, 2019 at 09:57:25AM +0100, Jon Hunter wrote:
>>> Hi Lorenzo,
>>>
>>> On 04/07/2019 17:09, Lorenzo Pieralisi wrote:
>>>> On Thu, Jul 04, 2019 at 08:34:28PM +0530, Vidya Sagar wrote:
>>>>> Currently Relaxed Ordering bit in the configuration space is enabled for
>>>>> all PCIe devices as the quirk uses PCI_ANY_ID for both Vendor-ID and
>>>>> Device-ID, but, as per the Technical Reference Manual of Tegra20 which is
>>>>> available at https://developer.nvidia.com/embedded/downloads#?search=tegra%202
>>>>> in Sec 34.1, it is mentioned that Relexed Ordering bit needs to be enabled in
>>>>> its root ports to avoid deadlock in hardware. The same is applicable for
>>>>> Tegra30 as well though it is not explicitly mentioned in Tegra30 TRM document,
>>>>> but the same must not be extended to root ports of other Tegra SoCs or
>>>>> other hosts as the same issue doesn't exist there.
>>>>>
>>>>> Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
>>>>
>>>> You forgot Thierry's ACK, I added it back but next time pay more
>>>> attention please.
>>>>
>>>> You should link the versions through eg git send-email
>>>> --in-reply-to=Message-Id so that it is easier to follow.
>>>>
>>>>> ---
>>>>> V3:
>>>>> * Modified commit message to make it more precise and explicit
>>>>>
>>>>> V2:
>>>>> * Modified commit message to include reference to Tegra20 TRM document.
>>>>>
>>>>>  drivers/pci/controller/pci-tegra.c | 7 +++++--
>>>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>>
>>>> I applied it to pci/tegra after rewriting the whole commit log and
>>>> adding a Fixes: tag that you or someone at Nvidia will follow up;
>>>> I will check.
>>>
>>> I had a chat with Vidya last night to understand the issue, so now I
>>> have a good understanding of the problem this has caused, which is very
>>> unfortunate indeed!
>>>
>>> Vidya mentioned that you would like us to get this backported to stable
>>> branches. Please correct me if I am wrong here. We can certainly do
>>> that, but I do have concerns about doing so, for non-Tegra devices
>>> inparticularly, given that this has been around for sometime now. Hence,
>>> I was wondering if we should leave this soak in the mainline for at
>>> least a kernel release cycle before doing so. I really don't want to
>>> break stable for anyone. What are your thoughts on this?
>>
>> I looped in Greg to pick his brain, since it is unclear how we should
>> apply the stable kernel rules on this specific patch. Basically, this
>> technically is not a bug, it is just bad code that forces a feature on
>> ALL kernels that compile the PCI Tegra Controller driver in the kernel.
>> I would really really want to have this patch applied to all stable
>> kernels but first as you said it is better to apply it to mainline and
>> check it does not cause any issues on any other arch/platform then
>> we can think about backporting it to stable kernels.
>>
>> I am not happy to force Relaxed Ordering on any PCIe device on
>> any platform/arch compiling PCI Tegra controller in, so somehow
>> we must rectify this situation, this is gross as I said before.
> 
> Yes understood. Let's plan to sync up on this once v5.3 is out and see
> how the land lies. We have an internal issue filed to track this and so
> we should not forget!

Please let us know if your preference it still to push this back to
stable. I assume that there has been no fallout from this change.

Cheers
Jon

-- 
nvpublic



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