[PATCH v2] drm: tilcdc: add a workaround for failed clk_set_rate()

[Bartosz Golaszewski]

2016-09-29 9:55 GMT+02:00 Jyri Sarha <jsarha at ti.com>:
> On 09/28/16 15:41, Bartosz Golaszewski wrote:
>> Some architectures don't use the common clock framework and don't
>> implement all the clk interfaces for every clock. This is the case
>> for da850-lcdk where clk_set_rate() only works for PLL0 and PLL1.
>>
>> Trying to set the clock rate for the LCDC clock results in -EINVAL
>> being returned.
>>
>> As a workaround for that: if the call to clk_set_rate() fails, fall
>> back to adjusting the clock divider instead. Proper divider value is
>> calculated by dividing the current clock rate by the required pixel
>> clock rate in HZ.
>>
>> This code is based on a hack initially developed internally for
>> baylibre by Karl Beldan <kbeldan at baylibre.com>.
>>
>> Tested with a da850-lcdk with an LCD display connected over VGA.
>>
>> Signed-off-by: Bartosz Golaszewski <bgolaszewski at baylibre.com>
>
> I'd say that a warn with backtrace over kill here (we know quite well
> how we end up here). And it would be helpful to know in actual numbers
> what the clock should have been and how close to it did we get.
>
> Otherwise the patch appears to work fine at least on am335x.
>

Actually there's one more issue - the requested clock rate is in
crtc->mode.clock, not in the rate variable, so that needs fixing too
for the message to be correct.

Best regards,
Bartosz Golaszewski