linux-kernel - Re: [PATCH v1 1/4] fbtft: Unorphan the driver

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Date:   Mon, 31 Jan 2022 13:36:26 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andy@...nel.org>, linux-fbdev@...r.kernel.org,
        Michael Hennerich <michael.hennerich@...log.com>,
        Helge Deller <deller@....de>, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Phillip Potter <phil@...lpotter.co.uk>,
        Carlis <zhangxuezhi1@...ong.com>,
        Lee Jones <lee.jones@...aro.org>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH v1 1/4] fbtft: Unorphan the driver

On Mon, Jan 31, 2022 at 09:29:33AM +0100, Javier Martinez Canillas wrote:
> On 1/26/22 15:15, Javier Martinez Canillas wrote:
> > On 1/26/22 15:10, Andy Shevchenko wrote:
> >> On Wed, Jan 26, 2022 at 04:08:32PM +0200, Andy Shevchenko wrote:
> >>> On Wed, Jan 26, 2022 at 02:46:08PM +0100, Javier Martinez Canillas wrote:
> >>>> On 1/26/22 14:12, Andy Shevchenko wrote:
> >>
> >> ...
> >>
> >>>> I've just bought a SSD1306 (I2C) based one and will attempt to write a DRM
> >>>> driver using drivers/staging/fbtft/fb_ssd1306.c as a reference.
> >>>
> >>> You should take ssd1307fb.c instead. And basically create a MIPI based driver
> >>> for I2C. Then we won't go same road again for other similar devices.
> >>
> >> For the record it supports your device:
> >>
> >> static const struct i2c_device_id ssd1307fb_i2c_id[] = {
> >> { "ssd1305fb", 0 },
> >> { "ssd1306fb", 0 },
> >> { "ssd1307fb", 0 },
> >> { "ssd1309fb", 0 },
> >>
> >>
> > 
> > Thanks a lot for the pointer. I was only looking at drivers/staging
> > and didn't check drivers/video. I'll try to convert that one then
> > once I get the display.
> > 
> 
> I got some time this weekend and was able to port the ssd1306 fbdev driver
> to DRM [0]. I'm not that familiar with the simple display pipe helpers, so
> there may be some wrong things there. But it does work and all the fbtests
> from https://git.kernel.org/pub/scm/linux/kernel/git/geert/fbtest.git pass.

Thanks! Good news, everybody!

> There are some hacks in the driver though. For example it exposes an XRGB8888
> format even thought the OLED display is monochromatic and has 1 bit per pixel.
> 
> The driver then goes and converts the XRGB8888 pixels first to grayscale and
> then to reverse mono. I took that idea from the repaper driver but that gives
> us the multiple copies that Geert was complaining about.
> 
> Another hack is that I am just hardcoding the {width, height}_mm, but I don't
> know what DPI could be used for these panels nor how I could calculate the mm.

I think the hacks is the first what should be eliminated, also see below.

...

> +config TINYDRM_SSD130X
> +	tristate "DRM support for Solomon SSD130X OLED displays"
> +	depends on DRM && OF && I2C

Please, make sure that it does NOT dependent on OF.

...

> +obj-$(CONFIG_TINYDRM_SSD130X)		+= ssd130x.o

I would keep the original name since we have I2C (fbdev) implementation, SPI
and platform (fbtft), and now i2c (drm). I would like to avoid more confusion
that we already have.

-- 
With Best Regards,
Andy Shevchenko