linux-kernel - Re: [PATCH v5 0/8] drm: rcar-du: Add Color Management Module (CMM)

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Message-ID: <20200527074422.GA27239@lxhi-065.adit-jv.com>
Date:   Wed, 27 May 2020 09:44:22 +0200
From:   Eugeniu Rosca <erosca@...adit-jv.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Eugeniu Rosca <erosca@...adit-jv.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Simon Horman <horms@...ge.net.au>,
        Ulrich Hecht <uli+renesas@...nd.eu>,
        <VenkataRajesh.Kalakodima@...bosch.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Koji Matsuoka <koji.matsuoka.xm@...esas.com>,
        <muroya@....co.jp>, <Harsha.ManjulaMallikarjun@...bosch.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Sean Paul <seanpaul@...omium.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michael Dege <michael.dege@...esas.com>,
        <gotthard.voellmeke@...esas.com>, <efriedrich@...adit-jv.com>,
        Michael Rodin <mrodin@...adit-jv.com>,
        <ChaitanyaKumar.Borah@...bosch.com>, <hien.dang.eb@...esas.com>,
        <michael.klein@...esas.com>, Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: Re: [PATCH v5 0/8] drm: rcar-du: Add Color Management Module (CMM)

Hi Geert,

On Wed, May 27, 2020 at 09:34:30AM +0200, Geert Uytterhoeven wrote:
> On Wed, May 27, 2020 at 9:16 AM Eugeniu Rosca <erosca@...adit-jv.com> wrote:
> > On Tue, Oct 15, 2019 at 12:46:13PM +0200, Jacopo Mondi wrote:
> > > CMM functionalities are retained between suspend/resume cycles (tested with
> > > suspend-to-idle) without requiring a re-programming of the LUT tables.
> >
> > Hmm. Is this backed up by any statement in the HW User's manual?
> > This comes in contrast with the original Renesas CMM implementation [**]
> > which does make use of suspend (where the freeze actually happens).
> >
> > Can we infer, based on your statement, that we could also get rid of
> > the suspend callback in [**]?
> 
> While the CMM state will be retained across suspend-to-idle, I'm quite
> sure it will be lost by suspend-to-RAM, at least on the Salvator-X(S),
> ULCB, and Ebisu development boards, as PSCI will ask the BD9571WMV
> regulator to power down the R-Car SoC.
> 
> So IMHO we do need suspend/resume handling.

That makes sense. I should be more careful about suspend-to-idle
vs suspend-to-ram and not alias the two.

-- 
Best regards,
Eugeniu Rosca