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

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Date:   Fri, 12 Jun 2020 18:10:05 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Jacopo Mondi <jacopo@...ndi.org>
Cc:     Eugeniu Rosca <erosca@...adit-jv.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        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 12, 2020 at 05:00:32PM +0200, Jacopo Mondi wrote:
> On Tue, Jun 09, 2020 at 04:29:59PM +0200, Eugeniu Rosca wrote:
> > On Sun, Jun 07, 2020 at 05:41:58AM +0300, Laurent Pinchart wrote:
> > > Note that the CMM driver is controlled by the DU driver. As the DU
> > > driver will reenable the display during resume, it will call
> > > rcar_du_cmm_setup() at resume time, which will reprogram the CMM. There
> > > should thus be no need for manual suspend/resume handling in the CMM as
> > > far as I can tell, but we need to ensure that the CMM is suspended
> > > before and resumed after the DU. I believe this could be implemented
> > > using device links.
> >
> > Based on below quote [*] from Jacopo's commit [**], isn't the device
> > link relationship already in place?
> 
> Yes, it's in place already.
> 
> I added pm_ops to cmm just to be able to printout when suspend/resume
> happens and the sequence is what comment [*] reports
> 
> [  222.909002] rcar_du_pm_suspend:505
> [  223.145497] rcar_cmm_pm_suspend:193
> 
> [  223.208053] rcar_cmm_pm_resume:200
> [  223.460094] rcar_du_pm_resume:513
> 
> However, Laurent mentioned that in his comment here that he expects
> the opposite sequence to happen (CMM to suspend before and resume after
> DU).
> 
> I still think what is implemented is correct:
> - CMM is suspended after DU: when CMM is suspended, DU is not feeding
>   it with data
> - CMM is resumed before: once DU restart operations CMM is ready to
>   receive data.
> 
> Laurent, what do you think ?

I think I shouldn't have written the previous e-mail in the middle of
the night :-) Suspending CMM after DU is obviously correct.

> > [*] Quote from commit [**]
> >    Enforce the probe and suspend/resume ordering of DU and CMM by
> >    creating a stateless device link between the two.
> >
> > [**] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8de707aeb45241
> >     ("drm: rcar-du: kms: Initialize CMM instances")

-- 
Regards,

Laurent Pinchart