linux-kernel - Re: [PATCH v5 2/2] drm: bridge: cdns-mhdp8546: Add support for DSC and FEC

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Message-ID: <d6l5vwx5s5oopyhniqbc3wputceblazpry2omeja2qvak37y2m@dbge4vedh7ko>
Date: Mon, 15 Sep 2025 21:53:32 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Harikrishna Shenoy <h-shenoy@...com>
Cc: andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
        Laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, airlied@...il.com, simona@...ll.ch,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, robh@...nel.org, krzk+dt@...nel.org,
        conor+dt@...nel.org, sjakhade@...ence.com, yamonkar@...ence.com,
        lumag@...nel.org, dianders@...omium.org, jani.nikula@...el.com,
        luca.ceresoli@...tlin.com, andy.yan@...k-chips.com,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, devarsht@...com, u-kumar1@...com,
        s-jain1@...com, tomi.valkeinen@...asonboard.com
Subject: Re: [PATCH v5 2/2] drm: bridge: cdns-mhdp8546: Add support for DSC
 and FEC

On Mon, Sep 15, 2025 at 02:06:58PM +0300, Dmitry Baryshkov wrote:
> On Mon, Sep 15, 2025 at 04:00:41PM +0530, Harikrishna Shenoy wrote:
> > From: Swapnil Jakhade <sjakhade@...ence.com>
> > 
> > Enable support for Display Stream Compression (DSC) in independent
> > mode with a single stream, along with Forward Error Correction (FEC)
> > in the Cadence MHDP8546 DisplayPort controller driver.
> > 
> > FEC is required when DSC is enabled to ensure reliable transmission
> > of the compressed stream.
> > 
> > Signed-off-by: Swapnil Jakhade <sjakhade@...ence.com>
> > Signed-off-by: Harikrishna Shenoy <h-shenoy@...com>
> > ---
> >  drivers/gpu/drm/bridge/cadence/Makefile       |   2 +-
> >  .../drm/bridge/cadence/cdns-mhdp8546-core.c   | 367 ++++++++-
> >  .../drm/bridge/cadence/cdns-mhdp8546-core.h   |  68 ++
> >  .../drm/bridge/cadence/cdns-mhdp8546-dsc.c    | 695 ++++++++++++++++++
> >  .../drm/bridge/cadence/cdns-mhdp8546-dsc.h    | 285 +++++++
> >  5 files changed, 1392 insertions(+), 25 deletions(-)
> >  create mode 100644 drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-dsc.c
> >  create mode 100644 drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-dsc.h
> > 
> > +		goto err;
> > +	}
> > +
> > +	if (ret > 0)
> > +		return 0;
> > +err:
> > +	return ret;
> > +}
> 
> Consider extracting a common helper and using it here and in the Intel
> DP driver. Also please use new DPCD helpers which return 0 instead of
> size.

For the reference, some time ago one of my colleagues implemented DP DSC
support for the drm/msm driver. It didn't go in for multiple reasons,
but feel free to use it as an inspiration for possible generic helpers.
See https://patchwork.freedesktop.org/series/113240/


-- 
With best wishes
Dmitry