linux-kernel - RE: [PATCH] cpufreq: imx6q: Only disabling 792MHz OPP for i.MX6ULL types below 792MHz

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Message-ID: <5aa0882abf84401a869ad37f7ee8c889@dh-electronics.com>
Date:   Wed, 8 Nov 2023 10:04:03 +0000
From:   Christoph Niedermaier <cniedermaier@...electronics.com>
To:     Fabio Estevam <festevam@...x.de>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sébastien Szymanski 
        <sebastien.szymanski@...adeus.com>, Stefan Agner <stefan@...er.ch>,
        Shawn Guo <shawnguo@...nel.org>, Marek Vasut <marex@...x.de>,
        NXP Linux Team <linux-imx@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] cpufreq: imx6q: Only disabling 792MHz OPP for i.MX6ULL
 types below 792MHz

From: Fabio Estevam
Sent: Tuesday, November 7, 2023 6:48 PM
> 
> Hi Christoph,
> 
> Thanks for your patch.
> 
> On 07/11/2023 13:31, Christoph Niedermaier wrote:
>> For a 900MHz i.MX6ULL CPU the 792MHz OPP is disabled. There is no
>> convincing reason to disable this OPP. If a CPU can run at 900MHz,
>> it should also be able to cope with 792MHz. Looking at the voltage
>> level of 792MHz in [1] (page 24, table 10. "Operating Ranges") the
>> current defined OPP is above the minimum. So the voltage level
>> shouldn't be a problem. Although in [2] (page 24, table 10.
>> "Operating Ranges") 792MHz isn't mentioned there isn't note that
>> 792MHz OPP isn't allowed. Change it to only disable 792MHz OPP for
> 
> I find this part:
> 
> "792MHz isn't mentioned there isn't note that 792MHz OPP isn't allowed."
> 
> a bit confusing.
> 
> Maybe:
> 
> "However in [2] (page 24, table 10. "Operating Ranges"), it is not
> mentioned that 792MHz OPP isn't allowed."

You are right, your suggestion expresses it more clearly.
I will change it in V2.

> 
> 
>> [1] https://www.nxp.com/docs/en/data-sheet/IMX6ULLIEC.pdf
>> [2] https://www.nxp.com/docs/en/data-sheet/IMX6ULLCEC.pdf
>>
>> Signed-off-by: Christoph Niedermaier <cniedermaier@...electronics.com>
>> Reviewed-by: Marek Vasut <marex@...x.de>
> 
> I think it is worth adding a Fixes tag so that this fix could be
> backported
> to stable kernels.

You mean the following fixes tag when the change was introduced?
Fixes: 0aa9abd4c212 ("cpufreq: imx6q: check speed grades for i.MX6ULL")
But if I'm right, then it goes down to version 4.19 and maybe the
commit 11a3b0ac33d9 ("cpufreq: imx6q: don't warn for disabling a non-existing frequency")
is also needed to easily apply.

Regards
Christoph