Re: State of affairs with Ilitek 9341 support

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Sat, Dec 23, 2023 at 11:00:32AM +0800, Dillon Min wrote:
> On Mon, 11 Dec 2023 at 21:19, Andy Shevchenko
> <andriy.shevchenko@intel.com> wrote:
> > On Fri, Dec 08, 2023 at 09:18:20PM +0100, Noralf Trønnes wrote:
> > > On 12/8/23 17:00, Andy Shevchenko wrote:

> > > > Included authors and latest (non-white-space) contributors to the drivers
> > > > in question along with relevant mailing list and respective (active in the
> > > > area) maintainers.
> > > >
> > > > I already had risen the question in times when 4th (sic!) driver for the same
> > > > hardware was about to be pulled into upstream that we have to somehow reduce
> > > > the code base and unify device properties.
> > > >
> > > > So, the main question here "What is the plan and where are we now?"
> > > >
> > > > I admit that fbtft case is special as it supports, in particular, platform
> > > > device (parallel interface) and also well established in the embedded world.
> > > > What about the rest?
> > > >
> > > > N.B. Besides the fact that panel drivers are too OF-centric, which is bad
> > > > practice for the new kernel code in general and has to be stopped. I.o.w.
> > > > seeing of_property_*() or alike in the driver after ca. 2020 should be
> > > > immediate NAK unless it's very well justified why it may not be used on
> > > > non-OF systems.
> >
> > Noralf, thanks for your response, my comments below.
> >
> > TBH I would also like to hear from maintainers, because it seems they got
> > an additional burden for no benefit.
> >
> > > Last year drivers/gpu/drm/tiny/panel-mipi-dbi.c was added to support all
> > > MIPI DBI compatible (ili9341) SPI displays.
> > > It loads the initialisation commands from a firmware file. For more info
> > > see https://github.com/notro/panel-mipi-dbi/wiki.
> > >
> > > When I started on fbtft in 2013 I didn't know about MIPI DBI so I made
> > > some common bus access functions and one driver per controller and that
> > > driver had an initialisation sequence to match the panel I had. Then I
> > > discovered that displays using the same controller could have different
> > > init sequences so I added a Device Tree <init> property that could
> > > override the driver init.
> > >
> > > In 2015 fbtft was added to drivers/staging, but later that year fbdev
> > > was closed for new drivers so it was a dead end.
> > >
> > > I started to work on porting fbtft to DRM and almost 2 years later
> > > support for the MI0283QT panel (ILI9341) was added.
> > > I had now learned about MIPI DBI so a library to handle that was added.
> > > I had asked on the Device Tree ML about the <init> property and I was
> > > told that I couldn't have that which meant that I couldn't get away with
> > > having just one driver for the MIPI DBI compatible display panels as I
> > > was first hoping for.
> > >
> > > I was aware that there was a challenge going from fbtft to DRM because
> > > in fbtft there is support for all panel setups using the <init>
> > > property, but in DRM every panel needed support in a driver. So I
> > > started to look at adding Device Tree properties to describe the setup
> > > for one controller. This would make it easy to describe a new panel in
> > > Device Tree for a supported controller. Maxime Ripard came up with the
> > > idea to have the controller initialisation commands in a firmware file
> > > which meant that we could get away with having just one driver for all
> > > MIPI DBI SPI panels (which is the vast majority of these SPI pixel
> > > upload panels).
> > >
> > > This meant that SPI support could be removed from all the MIPI DBI
> > > compatible controllers in fbtft
> >
> > I believe it can't. Otherwise we _must_ provide the DT (device property)
> > parser that uses what is provided for fbtft SPI to be enabled in the other
> > driver.
> >
> > > since there's now a solution for them in
> > > DRM. The drivers themselves must stay since they also have parallel bus
> > > support which is lacking in DRM. My plan was to wait for panel-mipi-dbi
> > > to hit an LTS and then either prepare patches to remove MIPI DBI SPI
> > > support from fbtft or at least send an email to staging about the new
> > > driver.
> >
> > > Unfortunately my health problems got worse and many plans went
> > > out the window.
> >
> > Oh, sad to hear this, hope you will get better sooner than later!
> >
> > > ILI9341 DRM drivers
> > >
> > > - drivers/gpu/drm/tiny/mi0283qt.c
> > >   This was the first driver added for the MI0283QT panel series
> > >
> > > - drivers/gpu/drm/tiny/ili9341.c
> > >   Later ili9341 based panels was decided to be added to a controller
> > >   specific driver.
> >
> > Why was it appeared in the first place? :-(
> >
> > > - drivers/gpu/drm/tiny/panel-mipi-dbi.c
> > >   Generic MIPI DBI SPI driver that loads init commands from a firmware
> > >   file. It uses of_property_read_string_index() and
> > >   of_get_drm_panel_display_mode(). I don't know if it's possible to make
> > >   device_property_*() versions of those.
> >
> > Everything like this is possible, just somebody needs to fulfill that.
> > And as I said, new OF-centric code, has to be NAKed by default.
> >
> > > - drivers/gpu/drm/panel/panel-ilitek-ili9341.c
> > >   This driver supports the MIPI DPI (RGB) interface on the controller.
> > >   Controller init is done over MIPI DBI SPI. The driver does also for
> > >   some reason support the same panel as the ili9341.c driver does.
> > >   So 2 drivers for the same panel...
> > >   Sidenote: It is possible to make a generic panel-mipi-dpi.c driver for
> > >   panels that use DPI for pixels and DBI for init loaded from a firmware
> > >   file.
> >
> > I wonder who has enough experience and time to at least point out or do
> > something about this...
> >
> > At least we can start combining the two in tinydrm, to reduce the variety.
> 
> I wrote drivers/gpu/drm/panel/panel-ilitek-ili9341.c to support ili9341
> on stm32f429-disco board via dbi or dpi.
> https://www.st.com/resource/en/schematic_pack/mb1075-f429i-c01_schematic.pdf
> 
> As one driver for one panel reason, so porting the mipi_dbi code and
> dts binding from tiny/ili9341.c
> It's true confused two driver for one panel in current kernel.
> I can remove the mipi_dbi code from panel-ilitek-ili9341.c or do something else.

FWIW, I have just sent this:
https://lore.kernel.org/r/20240813091258.1625646-1-andriy.shevchenko@linux.intel.com

> Anyway, I'd like to rewrite it based on the agreement.

-- 
With Best Regards,
Andy Shevchenko