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

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Date:   Wed, 27 May 2020 09:34:30 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Eugeniu Rosca <erosca@...adit-jv.com>
Cc:     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,
        Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: Re: [PATCH v5 0/8] drm: rcar-du: Add Color Management Module (CMM)

Hi Eugeniu,

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.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds