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

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Date:   Fri, 27 Sep 2019 16:47:46 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Adam Ford <aford173@...il.com>
CC:     Tony Lindgren <tony@...mide.com>, Tero Kristo <t-kristo@...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 15:33, Adam Ford wrote:

>> 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.
> 
> Is there anything I can do to help troubleshoot this?  I could insert
> a hack that checks if we're omap3 and if so make the divider equal to
> 4, but that seems like just a hack.
> I can run more tests or insert code somewhere if you want.

I think it's up to someone who's knowledgeable in omap clock framework. 
I'm kind of hoping that Tero or Tony would be willing to debug =). I can 
try to find time to debug the omap clk framework, but I'll be going on 
blindly there.

  Tomi

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