linux-kernel - Re: [PATCH 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

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Date:   Wed, 2 Feb 2022 09:38:51 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PWM List <linux-pwm@...r.kernel.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Mark Brown <broonie@...nel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        Maxime Ripard <maxime@...no.tech>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Peter Robinson <pbrobinson@...il.com>
Subject: Re: [PATCH 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED
 displays

Hello Sam,

On 2/1/22 21:40, Sam Ravnborg wrote:

[snip]

> 
> I took a look at the datasheets - and all ssd1305, ssd1306 and ssd1307
> are the same. They have timing constrains on the Vcc.
> The random schematic I found on the net showed me that a PWM was used to
> control the Vcc voltage - which again is used to control the brightness.
> 
> All the above has nothing to do with backlight - I had this mixed up in
> my head.
>

Yes, same here. I was leaning towards fixing the DT binding but then due
Geert comment and after reading the datasheets for ssd130{5,6,7} like you
I had the same understanding.

Glad that you agree.

[snip] 

> 
> Last I recommend to drop the fbdev variant - if the drm driver has any
> regressions we can fix them. And I do not see any other way to move
> users over. Unless their setup breaks then they do not change.
>

As I mentioned in this thread I wouldn't propose to drop the fbdev variant.
I prefer to use the carrot and not the stick. Peter Robinson suggested to
make the driver mutually exclusive and add !FB_SSD1307 in the config symbol.

I think that makes sense and will do it in v2.

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat