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

[Tero Kristo]

On 30/09/2019 18:10, Adam Ford wrote:
> On Mon, Sep 30, 2019 at 9:27 AM Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote:
> > On 30/09/2019 17:20, Tomi Valkeinen wrote:
> >
> > > Let's see what Tero says, but yeah, something is odd here. I expected
> > > the max divider to be 16 with Tero's patch, but I don't see it having
> > > that effect. I can get the div to 31.
> > >
> > > You can see this from the clock register 0x48004e40 (CM_CLKSEL_DSS). The
> > > lowest bits are the divider, 5 to 0. The TRM says max div is 32.
> > >
> > > Tero said for him the dividers > 16 didn't "stick" to the register. I'm
> > > now wondering if he has an old beagleboard with OMAP34xx, which has max
> > > div 16.
> >
> > So testing a bit more here, I can see the DSS working fine and fps as
> > expected when I write values directly to CM_CLKSEL_DSS:5:0, with
> > dividers up to 31. With 32, DSS breaks. The TRM (AM/DM37x) says value 32
> > is valid.
>
> I wonder if it's somehow being masked with bits 4:0 instead of 5:0
> which could potentially make the divider 0 and that value doesn't
> appear to be valid.

Hmmh, after some testing, it seems there is bad stuff happening with the 
divider clock implementation, I am re-working it as of now. Basically 
what is wrong is that with a divider max value of say 16, the driver 
attempts to craft the max value into a mask, but this ends up being 
0x1f. If the max value is 15, it ends up into 0xf which is correct.

-Tero
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