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

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Message-ID: <eb2eb1f6-3c9b-7ecb-667e-819033af9c14@ti.com>
Date:   Fri, 27 Sep 2019 18:47:54 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Tero Kristo <t-kristo@...com>, Adam Ford <aford173@...il.com>
CC:     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 27/09/2019 18:37, Tero Kristo wrote:

> If you can provide details about what clock framework / driver does 
> wrong (sample clk_set_xyz call sequence, expected results via 
> clk_get_xyz, and what fails), I can take a look at it. Just reporting 
> arbitrary display driver issues I won't be able to debug at all (I don't 
> have access to any of the displays, nor do I want to waste time 
> debugging them without absolutely no knowledge whatsoever.)

I used your hack patches to allow changing rates via debugfs. And set 
dss1_alwon_fck_3430es2 to 27000000 or 27870967. The end result was that 
DSS gets some very high clock from dss1_alwon_fck_3430es2, as the frame 
rate jumps to many hundreds fps.

So, these numbers are not real, but to give the idea what I saw. Running 
first with 50 MHz, I can see, say, 40 fps. Then I set the clock to 30 
MHz, and fps dropped to, say, 30fps, as expected with lower clock. Then 
I set the clock to 27MHz (or the other one), expecting a bit lower fps, 
but instead I saw hundreds of fps.

I don't know if there's any other way to observe the wrong clock rate 
but have the dss enabled and running kmstest or similar. I can help you 
set that up next week, should be trivial. You don't need a display for that.

  Tomi

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