Re: [PATCH 1/2] PWM: let of_xlate handlers check args count

From: Lothar WaÃmann
Date: Thu Jan 23 2014 - 05:57:31 EST


Sascha Hauer wrote:
> of_pwm_n_cells for the of_xlate handler is stored in struct pwm_chip,
> but it is only ever used by the of_xlate handler itsel. Remove
> of_pwm_n_cells from struct pwm_chip and let the handler do the argument
> count checking to simplify the code.
This still does not make the PWM_POLARITY flag in the pwms node
optional as was the goal because of_parse_phandle_with_args() requires
at least #pwm-cells arguments in the node.

So, with a DT configuration like:
pwm0: pwm@0 {
#pwm-cells = <3>;
backlight {
pwms = <&pwm0 0 100000>;
the driver will bail out at of_parse_phandle_with_args() in
of_pwm_get() with the error message:
"/backlight: arguments longer than property" and never reach your
clever xlate function.

Thus you will still need to replace of_parse_phandle_with_args()
with different code that copies most but not all of the functionality.

Lothar WaÃmann

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