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

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Date:   Fri, 5 Jun 2020 15:41:24 +0200
From:   Eugeniu Rosca <erosca@...adit-jv.com>
To:     Jacopo Mondi <jacopo@...ndi.org>
CC:     Eugeniu Rosca <erosca@...adit-jv.com>,
        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)

Hi Jacopo,

On Fri, Jun 05, 2020 at 03:29:00PM +0200, Jacopo Mondi wrote:
> On Wed, May 27, 2020 at 09:15:55AM +0200, Eugeniu Rosca wrote:
> > Could you kindly share the cross compilation steps for your kmsxx fork?
> 
> I usually build it on the target :)

Interesting approach. With ARM getting more and more potent, why not? :)

> 
> > 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 ?

Right.

> >
> > 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.

I see. JFYI, there is a flaw in the suspend handling in the out-of-tree
CMM patch [*], which renders the SoC unresponsive on HDMI hotplug. The
fix is currently under review. Hopefully it will make its way to [*]
in the nearest future. Just to keep in mind for the moment when CMM
s2ram will become a mainline feature.

> >
> > [*] 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