Petr Cvek <petr.cvek@xxxxxx> writes: > Dne 20.8.2015 v 22:01 Robert Jarzmik napsal(a): >> Petr Cvek <petr.cvek@xxxxxx> 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. You probably know that in a backlight case GPIO is just a subcase of PWM, with frequency equal to either 0 or max_backlight_freq. > 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'm in front of the same dilemna for 5 years ago with the mioa701 (64MB RAM, 2 * 32MB flash). I chose PWM, judging the PWM stack was worth it. Moreover, pwm can be a module, loaded or not : what memory do you spare in that case if you don't load the module ? > 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. I don't like changing the muxing after initialization that much : the pin muxing should represent what there is in hardware, and that is a backlight frequency switched input pin. The one exception is for hardware workarounds such as the AC97 reset pin. I won't take an init/exit with a manipulation of an mfp. I'll let you choose one way instead : - either the GPIO - or the PWM (module or not) Don't forget that this init/exit thing won't be available for a devicetree magician (if that happens). Cheers. -- Robert -- To unsubscribe from this list: send the line "unsubscribe linux-leds" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
