linux-kernel - Re: [PATCH v2 2/2] drm: fsl-dcu: enable PIXCLK on LS1021A

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Message-ID: <ovzeljss5uv6rymlbdfjolnjox3dklcv3v2km73gqnh6vejxvg@afhyhfwmt3nf>
Date: Fri, 27 Sep 2024 02:13:57 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Alexander Stein <alexander.stein@...tq-group.com>
Cc: Stefan Agner <stefan@...er.ch>, Alison Wang <alison.wang@....com>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Matthias Schiffer <matthias.schiffer@...group.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	Simona Vetter <simona@...ll.ch>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] drm: fsl-dcu: enable PIXCLK on LS1021A

On Thu, Sep 26, 2024 at 04:09:03PM GMT, Alexander Stein wrote:
> Hi Dmitry,
> 
> Am Donnerstag, 26. September 2024, 08:05:56 CEST schrieb Dmitry Baryshkov:
> > On Thu, Sep 26, 2024 at 07:55:51AM GMT, Alexander Stein wrote:
> > > From: Matthias Schiffer <matthias.schiffer@...group.com>
> > > 
> > > The PIXCLK needs to be enabled in SCFG before accessing certain DCU
> > > registers, or the access will hang. For simplicity, the PIXCLK is enabled
> > > unconditionally, resulting in increased power consumption.
> > 
> > By this description it looks like a fix. What is the first broken
> > commit? It needs to be mentioned in the Fixes: tag. Or is it hat
> > existing devices have been enabling SCFG in some other way?
> 
> We discussed this internally and it seems this never worked, unless PIXCLK
> was already enabled in SCFG by a different way, e.g. firmware, etc.

My bet was on the firmware, but I never touched Layerscape platforms.
Anyway,

Fixes: 109eee2f2a18 ("drm/layerscape: Add Freescale DCU DRM driver")
Acked-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>


> 
> Best regards,
> Alexander
> 
> > > 
> > > Signed-off-by: Matthias Schiffer <matthias.schiffer@...group.com>
> > > Signed-off-by: Alexander Stein <alexander.stein@...tq-group.com>
> > > ---
> > > Changes in v2:
> > > * Add note about power consumption in commit message
> > > * Add note about power consumption in comment
> > > * Fix alignment
> > > 
> > 
> > 
> 
> 
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> 
> 

-- 
With best wishes
Dmitry