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

From: "Pali Rohár" <pali@kernel.org>
To: Jason Hung <jhung@globalscaletechnologies.com>,
	Ken Ma <make@marvell.com>, Victor Gu <xigu@marvell.com>,
	Konstantin Porotchkin <kostap@marvell.com>,
	Nadav Haklai <nadavh@marvell.com>
Cc: "Marek Behún" <kabel@kernel.org>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Gregory CLEMENT" <gregory.clement@bootlin.com>,
	"Robert Marko" <robert.marko@sartura.hr>,
	"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, nnet <nnet@fastmail.fm>
Subject: Re: [PATCH v2] cpufreq: armada-37xx: forbid cpufreq for 1.2 GHz variant
Date: Fri, 2 Jul 2021 18:30:35 +0200	[thread overview]
Message-ID: <20210702163035.nmb5pniwpqtmaz4b@pali> (raw)
In-Reply-To: <20210630225601.6372-1-kabel@kernel.org>

+Jason from GlobalScale as this issue affects GlobalScale Espressobin Ultra and V7 1.2 GHz boards.

On Thursday 01 July 2021 00:56:01 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(-)
> 
> diff --git a/drivers/cpufreq/armada-37xx-cpufreq.c b/drivers/cpufreq/armada-37xx-cpufreq.c
> index 3fc98a3ffd91..c10fc33b29b1 100644
> --- a/drivers/cpufreq/armada-37xx-cpufreq.c
> +++ b/drivers/cpufreq/armada-37xx-cpufreq.c
> @@ -104,7 +104,11 @@ struct armada_37xx_dvfs {
>  };
>  
>  static struct armada_37xx_dvfs armada_37xx_dvfs[] = {
> -	{.cpu_freq_max = 1200*1000*1000, .divider = {1, 2, 4, 6} },
> +	/*
> +	 * The cpufreq scaling for 1.2 GHz variant of the SOC is currently
> +	 * unstable because we do not know how to configure it properly.
> +	 */
> +	/* {.cpu_freq_max = 1200*1000*1000, .divider = {1, 2, 4, 6} }, */
>  	{.cpu_freq_max = 1000*1000*1000, .divider = {1, 2, 4, 5} },
>  	{.cpu_freq_max = 800*1000*1000,  .divider = {1, 2, 3, 4} },
>  	{.cpu_freq_max = 600*1000*1000,  .divider = {2, 4, 5, 6} },
> -- 
> 2.31.1
> 

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