On Mon, Dec 11, 2023 at 03:19:08PM +0200, Andy Shevchenko 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. We never committed to supporting that binding in the first place, and that code is in staging, so I don't see why we must do that. > > 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? :-( It's probably an oversight. The name was far from obvious to begin with. > > - 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... I'm not sure it's worth it tbh. Panel drivers are fairly straightforward and easy to maintain, and getting a driver that can support all the variations of the power sequences those driver need would make a very complicated driver. And MIPI-DPI display are becoming more and more irrelevant. Small, cheap, display will keep using MIPI-DBI, and middle and high-end screens are using MIPI-DSI/eDP. Maxime
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