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

[Tomi Valkeinen]

(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@xxxxxx> 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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