linux-kernel - Re: [PATCH v4] amba: Remove deferred device addition

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Date:   Tue, 19 Jul 2022 14:39:31 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Russell King <linux@...linux.org.uk>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Rob Herring <robh@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] amba: Remove deferred device addition

On Mon, Jul 18, 2022 at 06:55:23PM -0700, Saravana Kannan wrote:
> On Wed, Jul 13, 2022 at 7:58 AM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Tue, Jul 12, 2022 at 12:38:33PM -0700, Saravana Kannan wrote:
> > > Sudeep,
> > >
> > > This makes me think the issue you are seeing is related to your
> > > hardware drivers. Can you look into those please? I'm leaning towards
> > > merging this amba clean up and adding delays (say 1ms) to your
> > > clock/power domain drivers to avoid the crash you are seeing. And then
> > > you can figure out the actual delays needed and update it.
> >
> > I haven't got a chance to debug the issue on Juno much further. One thing
> > about the platform is that we can't turn off the debug power domain that
> > most of the coresight devices share.
> >
> > One thing I also observed with -next+this patch is that with a little log
> > it can access the registers while adding first few devices and then crash
> > which doesn't align with platform behaviour as we can't turn off the domain
> > though we attached and turn on in amba_read_periphid and then turn off and
> > detach the power domain. Ideally if first device amba_read_periphid was
> > successful, it must be the case for all, but I see different behaviour.
> >
> > I need to check again to confirm if it is issue with platform power domain
> > driver. It is based on SCMI so there is some role played by the f/w as well.
> 
> Yeah, this log timing based behavior is what makes me suspect it's not
> a problem with this patch itself.
> 
> However, just to rule it out, can you try making this change on top of
> v4 and give it a shot? This is related to the issue Marek reported,
> but those are more about permanent probe failures. Not a crash.
>

This patch(version v4, fails to apply on -next but the conflict is trivial
and in the deleted code so I just retained your copy of all the functions)
plus the below change fixes the issue I reported on Juno.

I won't give you tested-by yet as you have plans to revert some things
and I resolved the conflict here though trivial, I prefer to apply the
patch as is with all associated changes and test once more.

Thanks for digging this and fixing it.

-- 
Regards,
Sudeep