Re: [PATCH v2 16/21] ARM: pxa: magician: Add support for alternative LCD backlight

Petr Cvek
2015-08-23T20:52:39Z

Dne 20.8.2015 v 22:01 Robert Jarzmik napsal(a):
> Petr Cvek <petr.cvek@tul.cz> writes:
>
>> Add support for alternative LCD backlight with GPIO (no brightness).
> Here, I don't understand, the commit message is too short.
>
> Are there 2 brightness controls on magician, or are these 2 different magicians
> (hardware wise), each having a different backlight control ? Or is it there is a
> GPIO to light up the screen and a PWM backlight ?
>
> I have to understand first.
>
I have aimed for a configuration, where user can use PWM xor GPIO backlight. As pin mux can set GPIO or PWM (or UART :-D) on PWM pin, you can choose if you spare few kB (as magician has only 64MB RAM and 64MB flash) on GPIO or will have smooth backlight with PWM.

I have tested both (I think I have added the gpio backlight for debugging a regression in pwm_bl).

Only ugly thing is the GPIO definition:

#if IS_ENABLED(CONFIG_PWM_PXA)
/* PWM 0 - LCD backlight */
GPIO16_PWM0_OUT,
#else
/* Ensure static backlight without any driver */
MFP_CFG_OUT(GPIO16, AF0, DRIVE_LOW), /* Backlight enabled */
#endif

Hmmm.. I think I can do this better in pwm-backlight init/exit (same way as pxa_ficp). During init the pin mux will switch to Alternate Function (PWM) and during exit it will switch to GPIO (which can be used by gpio-backlight). This will remove ugly ifdef.

Best regards,
Petr