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

[Javier Martinez Canillas]

Hello Mark,

On 2/8/22 16:18, Mark Brown wrote:
> On Tue, Feb 08, 2022 at 04:10:49PM +0100, Javier Martinez Canillas wrote:
>> On 2/8/22 15:19, Geert Uytterhoeven wrote:
> 
>>>   - "time ls" on the serial console (no files in the current directory,
>>>     so nothing to print) increases from 0.86s to 1.92s, so the system is
>>>     more loaded.  As ssd1307fb relied on deferred I/O too, the slowdown
>>>     might be (partly) due to redrawing of the visual artefacts
>>>     mentioned above.
> 
>> I was trying to first have the driver and then figure out how to optimize
>> it. For v3 I'm using regmap to access instead of the I2C layer directly.
> 
>> I noticed that this is even slower but it makes the driver more clean and
>> allows to support both I2C and SPI (untested but will include it as a WIP).
> 
> I wouldn't have expected regmap to add huge overhead relative to I2C,
> partly predicated on I2C being rather slow itself.  There will be some
> overhead for concurrency protection and data marshalling but for I2C
> clocked at normal speeds it's surprising.

Thanks for chiming in. That's good to know, I'll investigate more then.

Probably I was wrongly blaming regmap while it was another change that
is causing the display to be refreshed at a slower rate than before.

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