Re: [PATCH v2] cpufreq: armada-37xx: forbid cpufreq for 1.2 GHz variant

From: Viresh Kumar <viresh.kumar@linaro.org>
To: "Marek Behún" <kabel@kernel.org>
Cc: "Gregory CLEMENT" <gregory.clement@bootlin.com>,
	"Ken Ma" <make@marvell.com>, "Victor Gu" <xigu@marvell.com>,
	"Robert Marko" <robert.marko@sartura.hr>,
	"Pali Rohár" <pali@kernel.org>,
	"Tomasz Maciej Nowak" <tmn505@gmail.com>,
	"Anders Trier Olesen" <anders.trier.olesen@gmail.com>,
	"Philip Soares" <philips@netisense.com>,
	linux-pm@vger.kernel.org,
	"Sebastian Hesselbarth" <sebastian.hesselbarth@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	"Konstantin Porotchkin" <kostap@marvell.com>,
	nnet <nnet@fastmail.fm>, "Nadav Haklai" <nadavh@marvell.com>
Subject: Re: [PATCH v2] cpufreq: armada-37xx: forbid cpufreq for 1.2 GHz variant
Date: Thu, 1 Jul 2021 07:35:51 +0530	[thread overview]
Message-ID: <20210701020551.svhbjpbdw526cq7a@vireshk-i7> (raw)
In-Reply-To: <20210630225601.6372-1-kabel@kernel.org>

On 01-07-21, 00:56, Marek Behún wrote:
> The 1.2 GHz variant of the Armada 3720 SOC is unstable with DVFS: when
> the SOC boots, the WTMI firmware sets clocks and AVS values that work
> correctly with 1.2 GHz CPU frequency, but random crashes occur once
> cpufreq driver starts scaling.
> 
> We do not know currently what is the reason:
> - it may be that the voltage value for L0 for 1.2 GHz variant provided
>   by the vendor in the OTP is simply incorrect when scaling is used,
> - it may be that some delay is needed somewhere,
> - it may be something else.
> 
> The most sane solution now seems to be to simply forbid the cpufreq
> driver on 1.2 GHz variant.
> 
> Signed-off-by: Marek Behún <kabel@kernel.org>
> Fixes: 92ce45fb875d ("cpufreq: Add DVFS support for Armada 37xx")
> ---
> If someone from Marvell could look into this, it would be great since
> basically 1.2 GHz variant cannot scale, which is a feature that was
> claimed to be supported by the SOC.
> 
> Ken Ma / Victor Gu, you have worked on commit
> https://github.com/MarvellEmbeddedProcessors/linux-marvell/commit/d6719fdc2b3cac58064f41b531f86993c919aa9a
> in linux-marvell.
> Your patch takes away the 1202 mV constant for 1.2 GHz base CPU
> frequency and instead adds code that computes the voltages from the
> voltage found in L0 AVS register (which is filled in by WTMI firmware).
> 
> Do you know why the code does not work correctly for some 1.2 GHz
> boards? Do we need to force the L0 voltage to 1202 mV if it is lower,
> or something?
> ---
>  drivers/cpufreq/armada-37xx-cpufreq.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)

I am not picking it up for 5.14-rc1 to make sure others get a chance
to provide reviews.

-- 
viresh