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

[Andrew Lunn]

On Wed, Jun 30, 2021 at 03:59:42PM +0200, 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 at kernel.iorg>
> 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.
> ---
>  drivers/cpufreq/armada-37xx-cpufreq.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/cpufreq/armada-37xx-cpufreq.c b/drivers/cpufreq/armada-37xx-cpufreq.c
> index 3fc98a3ffd91..1ef3dde9a40b 100644
> --- a/drivers/cpufreq/armada-37xx-cpufreq.c
> +++ b/drivers/cpufreq/armada-37xx-cpufreq.c
> @@ -104,7 +104,13 @@ struct armada_37xx_dvfs {
>  };
>  
>  static struct armada_37xx_dvfs armada_37xx_dvfs[] = {
> +#if 0
> +	/*
> +	 * 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} },
> +#endif

I suspect you will get some drive by patches from bot handlers
removing the #if 0, since such code is not liked within the kernel,
and bot handlers blindly do what the bot tells them.

So i would suggest you avoid #if 0, and move the .cpu_req_max entry
into the comment.

     Andrew