linux-kernel - Re: [PATCH v1 2/2] drm/tinydrm: add driver for ILI9225 panels

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Message-ID: <20171204074507.t4ksonqammnflqqg@phenom.ffwll.local>
Date:   Mon, 4 Dec 2017 08:45:18 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     David Lechner <david@...hnology.com>,
        Stefano Babic <sbabic@...x.de>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:DRM PANEL DRIVERS" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v1 2/2] drm/tinydrm: add driver for ILI9225 panels

On Fri, Dec 01, 2017 at 03:03:30PM +0100, Linus Walleij wrote:
> On Wed, Nov 8, 2017 at 4:52 AM, David Lechner <david@...hnology.com> wrote:
> 
> > This adds a new driver for display panels based on the Ilitek ILI9225
> > controller.
> >
> > This was developed for a no-name panel with a red PCB that is commonly
> > marketed for Arduino. See <https://github.com/Nkawu/TFT_22_ILI9225>.
> >
> > I really did try very hard to find a make and model for this panel, but
> > there doesn't seem to be one, so the best I can do is offer the picture
> > in the link above for identification.
> >
> > Signed-off-by: David Lechner <david@...hnology.com>
> 
> Can you explain why tinydrm is not putting its panel drivers in
> drivers/gpu/drm/panel?
> 
> I guess everybody knows except me, it's usually like that :(
> 
> I am anyways working on a driver for Ilitek 9322 that I want
> to land in drivers/gpu/drm/panel. Here is the last iteration:
> https://lists.freedesktop.org/archives/dri-devel/2017-August/150205.html
> Yeah I got sidetracked. OK I will get to it now.
> 
> There are some similarities with the code I'm seeing here
> but I believe they are essentially different. But it will be hard
> to share code if you put the driver in the tinydrm framework.
> 
> I guess you have also seen:
> drivers/video/backlight/ili922x.c
> ?
> 
> Stefano Babic who wrote the backlight driver is available for
> reviewing, so includ him in follow-ups (added to To: line).
> 
> I'm putting you on CC as I'm rewriting it a bit after the DT
> maintainers review, will try to repost ASAP.

Bit more historical context: We tried using drm_panel in tinydrm, but that
didn't really fit to well (as Noralf explains, tinydrm is kinda more for
stand-alone panels). But tinydrm is also a bit too much midlayer-y still,
so there's a bunch of todo items capture in Documentation/gpu/todo.rst. In
the end we shouldn't need a special tinydrm driver, that should be covered
by the usual drm helpers.

Might be worth it to at least capture/summarize some of the reasons for
why tinydrm doesn't use drm_panel, and what it would take to better share
code (or maybe that's just a silly idea, not the first duplicated driver
in drm).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch