Re: [PATCH 0/2] drm: imx: Add NWL MIPI DSI host controller support

From: Shawn Guo <shawnguo@kernel.org>
To: Lucas Stach <l.stach@pengutronix.de>
Cc: "David Airlie" <airlied@linux.ie>,
	"Guido Günther" <agx@sigxcpu.org>,
	dri-devel@lists.freedesktop.org,
	"NXP Linux Team" <linux-imx@nxp.com>,
	"Pengutronix Kernel Team" <kernel@pengutronix.de>,
	"Robert Chiras" <robert.chiras@nxp.com>
Subject: Re: [PATCH 0/2] drm: imx: Add NWL MIPI DSI host controller support
Date: Tue, 28 May 2019 09:38:02 +0800	[thread overview]
Message-ID: <20190528013800.GB6885@dragon> (raw)
In-Reply-To: <1558964213.4039.2.camel@pengutronix.de>

Hi Lucas,

On Mon, May 27, 2019 at 03:36:53PM +0200, Lucas Stach wrote:
> We have been looking at how to support DCSS in mainline for a while,
> but most of the actual work got pushed behind in schedule due to other
> priorities.

I have some time to contribute.  Would you suggest how I should help
here?

1. You guys already have something close to completion and do not need
   more hands.
2. You guys already have some preliminary code and can use help from
   others.
3. You guys haven't got anything to start with, but just some design
   principles that anyone who wants to work on it should consider.

Which is the one that you want me to read?

> One thing I can can say for certain is that DCSS should not be
> integrated into imx-drm. It's a totally different hardware and
> downstream clearly shows that it's not a good idea to cram it into imx-
> drm.

I haven't gone deeper into the vendor code, but from a brief looking I
didn't see so many problems with integrating DCSS into imx-drm.  It's
not so unreasonable to take imx-drm as an imx-display-subsystem which
can have multiple CRTCs.  So can you please elaborate a bit on why it's
really a bad idea?

> Also the artificial split between hardware control in
> drivers/gpu/imx/dcss and the DRM driver is just cargo-cult from the
> IPU/imx-drm split. For the IPU we did it as the IPU has legs in both
> DRM for the output parts and V4L2 for the input parts. As the DCSS has
> no video input capabilities the driver could be simplified a lot by
> moving it all into a single DRM driver.

Agreed on this.

Shawn
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