[PATCH] drm/omap: Migrate minimum FCK/PCK ratio from Kconfig to dts

Tero Kristo t-kristo at ti.com
Fri Sep 27 15:37:35 UTC 2019

On 27/09/2019 16:47, Tomi Valkeinen wrote:
> On 27/09/2019 15:33, Adam Ford wrote:
>>> It looks like a bug in omap clock handling.
>>> DSS uses dss1_alwon_fck_3430es2 as fclk. dss1_alwon_fck_3430es2 comes
>>> from dpll4_ck, and there's a divider after the PLL, dpll4_m4_ck.
>>> When the DSS driver sets dss1_alwon_fck_3430es2 rate to 27000000 or
>>> 27870967, which can be created with m4 dividers 32 and 31, it looks like
>>> the divider goes to bypass, or to a very small value. DSS gets a very
>>> high clock rate and breaks down.
>> Is there anything I can do to help troubleshoot this?  I could insert
>> a hack that checks if we're omap3 and if so make the divider equal to
>> 4, but that seems like just a hack.
>> I can run more tests or insert code somewhere if you want.
> I think it's up to someone who's knowledgeable in omap clock framework. 
> I'm kind of hoping that Tero or Tony would be willing to debug =). I can 
> try to find time to debug the omap clk framework, but I'll be going on 
> blindly there.

If you can provide details about what clock framework / driver does 
wrong (sample clk_set_xyz call sequence, expected results via 
clk_get_xyz, and what fails), I can take a look at it. Just reporting 
arbitrary display driver issues I won't be able to debug at all (I don't 
have access to any of the displays, nor do I want to waste time 
debugging them without absolutely no knowledge whatsoever.)

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