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

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Message-ID: <CAHCN7xJNJca8W_yw5nNY3AmKDSPoLzJ8voPmR1HS3bNcU8uQGg@mail.gmail.com>
Date:   Mon, 30 Sep 2019 10:10:11 -0500
From:   Adam Ford <aford173@...il.com>
To:     Tomi Valkeinen <tomi.valkeinen@...com>
Cc:     "H. Nikolaus Schaller" <hns@...delico.com>,
        Tero Kristo <t-kristo@...com>,
        Tony Lindgren <tony@...mide.com>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Adam Ford <adam.ford@...icpd.com>,
        Benoît Cousson <bcousson@...libre.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/omap: Migrate minimum FCK/PCK ratio from Kconfig to dts

On Mon, Sep 30, 2019 at 9:27 AM Tomi Valkeinen <tomi.valkeinen@...com> 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.

adam

>
>   Tomi
>
> --
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