linux-kernel - Re: [PATCH 03/13] opp: Keep track of currently programmed OPP

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Date:   Mon, 25 Jan 2021 08:42:29 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Sibi Sankar <sibis@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 03/13] opp: Keep track of currently programmed OPP

On 22-01-21, 17:31, Dmitry Osipenko wrote:
> This may not be true for all kinds of hardware, a display controller is
> one example. If display's pixclock is raised before the memory bandwidth
> of the display's memory client, then display controller may get a memory
> underflow since it won't be able to fetch memory fast enough and it's
> not possible to pause data transmission to display panel, hence display
> panel may get out of sync and a full hardware reset will be needed in
> order to recover. At least this is the case for NVIDIA Tegra SoCs.

Hmm, but I expected that the request for more data will only come after the
opp-set-rate has finished and not in between. May be I am wrong. There is
nothing wrong in doing it the regulator way if required.

> I guess it's not a real problem for any of OPP API users right now, but
> this is something to keep in mind.

Sure, I am not against it. Just that we thought it isn't worth the code.

-- 
viresh