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

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On Fri, Jul 05, 2019 at 10:38:59AM +0100, 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.

You all have read the stable kernel rules, right:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

Patches have to be upstream first.

After it is merged in Linus's tree, post the patches with the git commit
ids to stable@vger and we will be glad to review them there.

thanks,

greg k-h



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