[PATCH v3 0/2] drm/imx/lcdc: Implement DRM driver for imx21

[Uwe Kleine-König]

Hello Rob,

On Tue, Dec 20, 2022 at 12:19:48PM -0600, Rob Herring wrote:
> On Sat, Dec 17, 2022 at 07:38:06PM +0100, Uwe Kleine-König wrote:
> > On Fri, Dec 16, 2022 at 05:57:58PM -0600, Rob Herring wrote:
> > > On Fri, Dec 16, 2022 at 06:50:04PM +0100, Uwe Kleine-König wrote:
> > > > Hello,
> > > > 
> > > > Changes since v2:
> > > > 
> > > >  - added allOf as Krzysztof requested
> > > >  - reworked driver based on Philipp's comments
> > > >    (improved error handling, different selects, moved driver to a subdirectory,
> > > >    header sorting, drm_err instead of DRM_ERROR, inlined
> > > >    imx_lcdc_check_mode_change, make use of dev_err_probe())
> > > >  
> > > > Krzysztof also pointed out that we're now having two compatibles for a
> > > > single hardware. Admittedly this is unusual, but this is the chance that
> > > > the (bad) compatible identifier imx21-fb gets deprecated. The hardware
> > > > is called LCDC and only the linux (framebuffer) driver is called imxfb.
> > > 
> > > The problem is you can't have firmware (with the DTB) that supports 
> > > both. Well, you can if you want to have some firmware setting that 
> > > selects which one. Otherwise, it's really an OS problem to decide what 
> > > to use. 
> > 
> > I don't understand what you intend to say here. The same applies if the
> > compatible is the same for both binding alternatives, isn't it? 
> 
> Only if you have both nodes in the DT and both enabled. But 2 enabled 
> nodes at the same address is also a dtc warning, so I was assuming you 
> didn't do that.

My idea was to use the new compatible in the soc.dtsi, and the old one
in the soc-machine.dts until they are converted. And then eventually
drop the old driver.

> > Do you consider a firmware problem better or an OS problem?
> 
> The OS created the problem, so they get to keep it. But a PC BIOS is 
> full of OS compatibility switches, so...
> 
> In the end, it's the platforms' decision really. I just want what the 
> implications of having 2 compatibles are to be understood.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |
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