linux-kernel - Re: [PATCH 2/2] ARM: omap5/dra7xx: Fix counter frequency drift for AM572x errata i856.

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Date:	Wed, 17 Dec 2014 17:45:05 +0200
From:	Tero Kristo <t-kristo@...com>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Nishanth Menon <nm@...com>
CC:	Lokesh Vutla <lokeshvutla@...com>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH 2/2] ARM: omap5/dra7xx: Fix counter frequency drift for
 AM572x errata i856.

On 12/17/2014 05:27 PM, Lennart Sorensen wrote:
> On Wed, Dec 17, 2014 at 09:22:25AM -0600, Nishanth Menon wrote:
>> A clock mux might do the job?
>>
>> value 1, 2 , 3 will imply sysclk1 / 610
>> value of 0 implies fixed 32768
>>
>> soemthing like
>> sys_clk32_crystal {
>>                 compatible = "fixed-clock";
>>                 clock-frequency = <32768>;
>> }
>>
>> sys_clk32_pseudo {
>>                 compatible = "fixed-clock";
>>                 compatible = "fixed-factor-clock";
>>                 clocks = <&sys_clkin1>;
>>                 clock-mult = <1>;
>>                 clock-div = <610>;
>> }
>>
>> sys_32k_ck: sys_32k_ck {
>> 	compatible = "ti,mux-clock";
>> 	clocks = <&sys_clk32_crystal>, <&sys_clk32_pseudo>, <&sys_clk32_pseudo>, <&sys_clk32_pseudo>;
>> };
>>
>> I think... The only issue is that the BOOTSTRAP register is not around
>> the usual CM1,2 address region...
>
> OK, I like where that idea is headed.  That looks promising.
>

Yea clock mux can be used. However, we don't have support for DRA7 
control module clocks in the DT yet. I have posted patches with support 
towards this a couple of weeks back, but they need some revising.

Thus, we maybe need to apply the timer patches as is for now, and fix 
the clock tree a bit later.

-Tero

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