linux-kernel - Re: [PATCH v6 3/6] drm: Add driver for Solomon SSD130x OLED displays

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Date:   Wed, 9 Mar 2022 21:13:51 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Maxime Ripard <maxime@...no.tech>,
        Noralf Trønnes <noralf@...nnes.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Lee Jones <lee.jones@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Linux PWM List <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v6 3/6] drm: Add driver for Solomon SSD130x OLED displays

Hello Geert,

On 3/9/22 21:04, Geert Uytterhoeven wrote:

[snip]

>> +
>> +               /* Last page may be partial */
>> +               if (8 * (i + 1) > ssd130x->height)
>> +                       m = ssd130x->height % 8;
>> +               for (j = x; j < x + width; j++) {
>> +                       u8 data = 0;
>> +
>> +                       for (k = 0; k < m; k++) {
>> +                               u8 byte = buf[(8 * i + k) * line_length + j / 8];
> 
> As buf does not point to (0, 0), the above is not correct if rect.x1 !=
> 0 or rect.y1 != 0.  After fixing that, writing more than one text line
> to the console works, but I still see an issue with updates where the
> rectangle size and/or position are not aligned to 8 pixels horizontally.
> Will do more investigation, and send fixes...
>

Right, I believe this is a consequence of introducing shadow buffers at
some point and not adjusting the logic in this function.

Thanks a lot for tracking down the issues and working on fixes for them!
 -- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat