Commit ea95b299 authored by Uwe Kleine-König's avatar Uwe Kleine-König Committed by Thierry Reding
Browse files

pwm: twl-led: Document some limitations and link to the reference manual 



I found these just from reading the reference manual and the driver
source. It's unclear to me if there are glitches when updating the ON
and OFF registers.

Signed-off-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 3391780b

drivers/pwm/pwm-twl-led.c

+16 −0
Original line number Diff line number Diff line
@@ -7,6 +7,22 @@ 
 *

 * This driver is a complete rewrite of the former pwm-twl6030.c authorded by:

 * Hemanth V <hemanthv@ti.com>

 *

 * Reference manual for the twl6030 is available at:

 * https://www.ti.com/lit/ds/symlink/twl6030.pdf

 *

 * Limitations:

 * - The twl6030 hardware only supports two period lengths (128 clock ticks and

 *   64 clock ticks), the driver only uses 128 ticks

 * - The hardware doesn't support ON = 0, so the active part of a period doesn't

 *   start at its beginning.

 * - The hardware could support inverted polarity (with a similar limitation as

 *   for normal: the last clock tick is always inactive).

 * - The hardware emits a constant low output when disabled.

 * - A request for .duty_cycle = 0 results in an output wave with one active

 *   clock tick per period. This should better use the disabled state.

 * - The driver only implements setting the relative duty cycle.

 * - The driver doesn't implement .get_state().

 */



#include <linux/module.h>