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

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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: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
This commit is contained in:
Uwe Kleine-König 2022-07-12 10:46:56 +02:00 committed by Thierry Reding
parent 3391780b74
commit ea95b29983
1 changed files with 16 additions and 0 deletions
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16
drivers/pwm/pwm-twl-led.c
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@ -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>