linux-kernel - Re: [RFC] dt-bindings: mailbox: add doorbell support to ARM MHU

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Date:   Thu, 4 Jun 2020 10:20:52 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rob Herring <robh@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Frank Rowand <frowand.list@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] dt-bindings: mailbox: add doorbell support to ARM MHU

On Wed, Jun 03, 2020 at 01:32:42PM -0500, Jassi Brar wrote:
> On Wed, Jun 3, 2020 at 1:04 PM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Fri, May 29, 2020 at 09:37:58AM +0530, Viresh Kumar wrote:
> > > On 28-05-20, 13:20, Rob Herring wrote:
> > > > Whether Linux
> > > > requires serializing mailbox accesses is a separate issue. On that side,
> > > > it seems silly to not allow driving the h/w in the most efficient way
> > > > possible.
> > >
> > > That's exactly what we are trying to say. The hardware allows us to
> > > write all 32 bits in parallel, without any hardware issues, why
> > > shouldn't we do that ? The delay (which Sudeep will find out, he is
> > > facing issues with hardware access because of lockdown right now)
> >
> > OK, I was able to access the setup today. I couldn't reach a point
> > where I can do measurements as the system just became unusable with
> > one physical channel instead of 2 virtual channels as in my patches.
> >
> > My test was simple. Switch to schedutil and read sensors periodically
> > via sysfs.
> >
> >  arm-scmi firmware:scmi: message for 1 is not expected!
> >
> This sounds like you are not serialising requests on a shared channel.
> Can you please also share the patch?

OK, I did try with a small patch initially and then realised we must hit
issue with mainline as is. Tried and the behaviour is exact same. All
I did is removed my patches and use bit[0] as the signal. It doesn't
matter as writes to the register are now serialised. Oh, the above
message comes when OS times out in advance while firmware continues to
process the old request and respond.

The trace I sent gives much better view of what's going on.

--
Regards,
Sudeep