linux-kernel - Re: [PATCH v2 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

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Date:   Wed, 9 Feb 2022 15:42:16 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux PWM List <linux-pwm@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Mark Brown <broonie@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Maxime Ripard <maxime@...no.tech>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Lee Jones <lee.jones@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v2 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED
 displays

Hello Geert,

On 2/9/22 15:27, Geert Uytterhoeven wrote:
> Hi Andy,
> 
> On Wed, Feb 9, 2022 at 2:48 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
>> On Tue, Feb 08, 2022 at 04:10:49PM +0100, Javier Martinez Canillas wrote:
>>> On 2/8/22 15:19, Geert Uytterhoeven wrote:
>>>> On Fri, Feb 4, 2022 at 2:43 PM Javier Martinez Canillas
>>>> <javierm@...hat.com> wrote:
>>>>   - Kernel size increased by 349 KiB,
>>>>   - The "Memory:" line reports 412 KiB less memory,
>>>>   - On top of that, "free" shows ca. 92 KiB more memory in use after
>>>>     bootup.
>>
>> The memory consumption should really be taken seriously, because these kind of
>> displays are for embedded platforms with limited amount of resources.
> 
> Thanks for your concern!
> 
> Looking at the options that are auto-enabled, a few stand out that
> look like they're not needed on systems witch such small displays,
> or on legacy systems predating DDC:

Thanks for your analysis.

Since drivers are replacing the {simple,efi}fb drivers and others with the
simpledrm driver, the DRM subsystem is now built into the kernel and no
longer a loadable module.

So there has been some effort to make it more modular and smaller, as an
example the following patch-set from Thomas:

https://www.spinics.net/lists/dri-devel/msg329120.html

But there are still a lot of room to reduce this and certainly enabling
CONFIG_DRM will be noticeable for such memory constrainted systems.

This is outside the scope of this patch series though, that is only about
adding a new DRM driver :)

Now, this is a reason why I mentioned that the old fbdev driver shouldn't
be removed yet.

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