linux-kernel - Re: [PATCH v2 2/4] drm/tiny: Add driver for Solomon SSD130X OLED displays

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Date:   Sat, 5 Feb 2022 15:04:22 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-fbdev@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
        dri-devel@...ts.freedesktop.org,
        Noralf Trønnes <noralf@...nnes.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maxime Ripard <maxime@...no.tech>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Lee Jones <lee.jones@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v2 2/4] drm/tiny: Add driver for Solomon SSD130X OLED
 displays

On Fri, Feb 04, 2022 at 08:19:12PM +0100, Javier Martinez Canillas wrote:
> On 2/4/22 15:26, Andy Shevchenko wrote:
> > On Fri, Feb 04, 2022 at 02:43:45PM +0100, Javier Martinez Canillas wrote:

...

> >> +struct ssd130x_device {
> >> +	struct drm_device drm;
> >> +	struct drm_simple_display_pipe pipe;
> >> +	struct drm_display_mode mode;
> >> +	struct drm_connector connector;
> > 
> > 
> >> +	struct i2c_client *client;
> > 
> > Can we logically separate hw protocol vs hw interface from day 1, please?
> > This will allow to add SPI support for this panel much easier.
> > 
> > Technically I would like to see here
> > 
> > 	struct device *dev;
> >
> > and probably (I haven't looked into design)
> > 
> > 	struct ssd130x_ops *ops;
> > 
> > or something alike.
> 
> Sure. I wanted to keep the driver simple, making the writes bus agnostic and
> adding a level of indirection would make it more complex. But I agree that
> it will also make easier to add more buses later. I will do that for v3.

I have SSD1306 display with SPI interface and I'm not able to test your series.
With the above it at least gives me a point to consider helping (coding and
testing)  with SPI one.

...

> >> +	if (!fb)
> >> +		return;
> > 
> > Can it happen?
> 
> I don't know, but saw that the handler of other drivers checked for this so
> preferred to play safe and do the same.

So, either cargo-cult or indeed it may happen. Somebody may conduct a research
on this...

...

> >> +	drm_mode_probed_add(connector, mode);
> >> +	drm_set_preferred_mode(connector, mode->hdisplay, mode->vdisplay);
> >> +
> >> +	return 1;
> > 
> > Positive code, what is the meaning of it?
> 
> It's the number of connector modes. The driver only supports 1.

A comment then?

-- 
With Best Regards,
Andy Shevchenko