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

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Message-Id: <BCB0237F-1AF7-4603-A778-8944C3618BC7@goldelico.com>
Date:   Mon, 30 Sep 2019 16:56:39 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Tomi Valkeinen <tomi.valkeinen@...com>
Cc:     Adam Ford <aford173@...il.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


> Am 30.09.2019 um 16:27 schrieb Tomi Valkeinen <tomi.valkeinen@...com>:
> 
> 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.

Just a blind guess: is there something in the errata to take care of?