linux-kernel - Re: [PATCH v6 2/4] drm/imx: Add initial support for DCSS on iMX8MQ

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Message-ID: <20200718115734.GA2989793@ravnborg.org>
Date:   Sat, 18 Jul 2020 13:57:34 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Guido Günther <agx@...xcpu.org>
Cc:     Laurentiu Palcu <laurentiu.palcu@....nxp.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Lucas Stach <l.stach@...gutronix.de>, lukas@...mn.com,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 2/4] drm/imx: Add initial support for DCSS on iMX8MQ

On Sat, Jul 18, 2020 at 01:05:25PM +0200, Guido Günther wrote:
> Hi,
> On Fri, Jul 17, 2020 at 09:48:49PM +0200, Sam Ravnborg wrote:
> > Hi Laurentiu.
> > 
> > On Fri, Jul 17, 2020 at 05:41:27PM +0300, Laurentiu Palcu wrote:
> > > From: Laurentiu Palcu <laurentiu.palcu@....com>
> > > 
> > > This adds initial support for iMX8MQ's Display Controller Subsystem (DCSS).
> > > Some of its capabilities include:
> > >  * 4K@...ps;
> > >  * HDR10;
> > >  * one graphics and 2 video pipelines;
> > >  * on-the-fly decompression of compressed video and graphics;
> > > 
> > > The reference manual can be found here:
> > > https://www.nxp.com/webapp/Download?colCode=IMX8MDQLQRM
> > > 
> > > The current patch adds only basic functionality: one primary plane for
> > > graphics, linear, tiled and super-tiled buffers support (no graphics
> > > decompression yet), no HDR10 and no video planes.
> > > 
> > > Video planes support and HDR10 will be added in subsequent patches once
> > > per-plane de-gamma/CSC/gamma support is in.
> > > 
> > > Signed-off-by: Laurentiu Palcu <laurentiu.palcu@....com>
> > > Reviewed-by: Lucas Stach <l.stach@...gutronix.de>
> > > ---
> > 
> > ....
> >         return drm_bridge_attach(encoder, bridge, NULL, 0);
> > ....
> > 
> > The above code-snippet tells that the display-driver rely on the bridge
> > to create the connector.
> > Could this by any chance be updated to the new way where the display
> > driver creates the connector - and thus passing DRM_BRIDGE_ATTACH_NO_CONNECTOR
> > as the flags argument?
> > 
> > What bridges would be relevant?
> > To check that the reelvant bridges are already ported.
> 
> I think that's mostly NWL atm since MHDP isn't mainline yet. Can you
> recommend a bridge driver to look at that does this right?

Hi Guido.

The following is from my notes:

bridge/adv7511                         done
bridge/simple-bridge                   done
bridge/synopsys/dw-hdmi                done
bridge/display-connector.c             done
bridge/lvds-codec                      done
bridge/cdns-dsi                        done
bridge/panel.c                         done
bridge/parade-ps8640                   done
bridge/sil-sii8620                     done
bridge/synopsys/dw-mipi-dsi            done
bridge/tc358768                        done
bridge/thc63lvd1024                    done
bridge/ti-tfp410                       done

This is a list of bridge drivers which are converted and in
drm-misc-next now.
I have a patch set that converts some more but they needs a bit more
polishing before they are done.

Laurent has written about is in a very comprehensive way several times.
The short variant is that we needed to support chained bridges where
the individual bridges implemented the functions required by the
connector - and creating the connector was pushed back to the display
driver.
So the bridges now announce their support of for example hot-plug detect
and reading edid. Then the connector, created by the display driver, can
use the operations exported by the bridge drivers.

	Sam