Re: Controllers with several interface options - one or more drivers?

From: Daniel Vetter <daniel@ffwll.ch>
To: Sam Ravnborg <sam@ravnborg.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Andrzej Hajda <a.hajda@samsung.com>
Cc: devicetree <devicetree@vger.kernel.org>,
	Dave Airlie <airlied@linux.ie>,
	Josef Lusticky <josef@lusticky.cz>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Thierry Reding <thierry.reding@gmail.com>
Subject: Re: Controllers with several interface options - one or more drivers?
Date: Fri, 26 Jul 2019 17:06:03 +0200	[thread overview]
Message-ID: <CAKMK7uESP5D4e_Qx6W7amURqxJ=5Y4JHduZYCtkyVQY9jKJQeA@mail.gmail.com> (raw)
In-Reply-To: <20190726145513.GK15868@phenom.ffwll.local>

Also probably should add a few more (drm_bridge) people, I think
that's also somewhat relevant here.
-Daniel

On Fri, Jul 26, 2019 at 4:55 PM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Fri, Jul 26, 2019 at 02:25:10PM +0200, Sam Ravnborg wrote:
> > Hi Josef, Daniel et al.
> >
> > The driver that triggered this reply is a driver that adds parallel
> > support to ili9341 in a dedicated panel driver.
> > The issue here is that we already have a tiny driver that supports the
> > ili9341 controller - but with a slightly different configuration.
> >
> > The ili9341 supports several interfaces - from the datasheet:
> >     "ILI9341 supports parallel 8-/9-/16-/18-bit data bus
> >      MCU interface, 6-/16-/18-bit data bus RGB interface and
> >      3-/4-line serial peripheral interface (SPI)"
> >
> > Noralf - in another mail explained:
> > "
> > The MIPI Alliance has lots of standards some wrt. display controller
> > interfaces:
> > - MIPI DBI - Display Bus Interface (used for commands and optionally pixels)
> > - MIPI DPI - Display Pixel Interface (also called RGB interface or
> > DOTCLK interface)
> > - MIPI DSI - Display Serial Interface (commands and pixels)
> >
> > The ili9341 supports both MIPI DBI and DPI.
> > "
> >
> > MIPI DPI - is a good fit for a drm_panel driver.
> > MIPI DBI - requires a full display controller driver.
> >
> > There are many other examples of driver SoC that in the same way
> > can be seen only as a panel or as a full display controller driver.
> >
> > The open question here is if we should try to support both cases in the
> > same driver / file. Or shall we implment two different drivers.
> > One for the panel use-case. And one for the display controller usecase?
> >
> > Not sure - so asking for feedback.
>
> I'm not sure. Currently we do have DSI and dumb RGB panels all in
> drm/panel. I don't think we have DBI panels in there yet, but then
> drm/tiny is the only one supporting these.
>
> I guess we could look into move some of the DBI panel drivers into panel
> drivers, but that needs a bit more glue all around. I'm honestly not sure
> how the current DSI drivers in drm_panel work exactly, especially for
> command mode.
>
> Or maybe we need a new interface for command mode.
>
> Wrt sharing code between drivers for the same chip, but different
> interfaces: I wouldn't worry too much about that. Maybe try to have a
> shared header file at least for registers. Long term we could end up with
> one driver module which exposes different flavours of the same chip, so
> multiple drm_panel drivers, or maybe we'll get something more specific for
> dsi/dbi.
> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch


-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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