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

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Date:   Fri, 5 Jun 2020 15:29:00 +0200
From:   Jacopo Mondi <jacopo@...ndi.org>
To:     Eugeniu Rosca <erosca@...adit-jv.com>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        laurent.pinchart@...asonboard.com,
        kieran.bingham+renesas@...asonboard.com, geert@...ux-m68k.org,
        horms@...ge.net.au, uli+renesas@...nd.eu,
        VenkataRajesh.Kalakodima@...bosch.com, airlied@...ux.ie,
        daniel@...ll.ch, koji.matsuoka.xm@...esas.com, muroya@....co.jp,
        Harsha.ManjulaMallikarjun@...bosch.com, ezequiel@...labora.com,
        seanpaul@...omium.org, linux-renesas-soc@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        michael.dege@...esas.com, gotthard.voellmeke@...esas.com,
        efriedrich@...adit-jv.com, 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)

Hello Eugeniu,
   sorry for the late reply

On Wed, May 27, 2020 at 09:15:55AM +0200, Eugeniu Rosca wrote:
> Hi Jacopo,
>
> On Tue, Oct 15, 2019 at 12:46:13PM +0200, Jacopo Mondi wrote:
>  ----8<---
>
> > * Testing
> > I have tested by injecting a color inversion LUT table and enabling/disabling it
> > every 50 displayed frames:
> > https://jmondi.org/cgit/kmsxx/log/?h=gamma_lut
>
> Could you kindly share the cross compilation steps for your kmsxx fork?
>

I usually build it on the target :)

> Just out of curiosity, have you ever tried to pull the display's HDMI
> cable while reading from CM2_LUT_TBL?

Ahem, not really :) Did I get you right, you mean disconnecting the
HDMI cable from the board ?

>
> At least with the out-of-tree CMM implementation [*], this sends the
> R-Car3 reference targets into an unrecoverable freeze, with no lockup
> reported by the kernel (i.e. looks like an serious HW issue).
>
> >
> > 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 [**]?

As Geert (thanks) explained what I've tested with is suspend-to-idle,
which retains the state of the LUT tables (and I assume other
not-yet-implemented CMM features, like CLU). I recall the out-of-tree
driver has suspend/resume routines but I never really tested that.

Thanks
   j

>
> [*] https://github.com/renesas-rcar/du_cmm
> [**] https://github.com/renesas-rcar/du_cmm/blob/c393ed49834bdbc/meta-rcar-gen3/recipes-kernel/linux/linux-renesas/0001-drm-rcar-du-Add-DU-CMM-support.patch#L1912
>
> --
> Best regards,
> Eugeniu Rosca