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SubjectRe: [PATCH] drm/omap: Migrate minimum FCK/PCK ratio from Kconfig to dts
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(dropping folks who're probably not interested...)

On 26/09/2019 17:12, Adam Ford wrote:
> On Thu, Sep 26, 2019 at 1:55 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
>>
>> On 25/09/2019 23:51, Adam Ford wrote:
>>
>>>> Has anyone debugged why the hang is happening?
>>> I started to debug this, but I got distracted when I noticed the LCD
>>> did't work at all on modern kernels. I have that fixed now, so I can
>>> go back to investigating this.

I dont' have the same board, but I was testing with omap3 beagle xm. I
can reproduce rather similar issue, although I don't get a hang but
instead sync lost and underflow flood (which makes the device unusable).

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.

Tomi

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Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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