[PATCH] firmware: arm_scmi: Warn if domain frequency multiplier is 0 or rounded off

[Pierre Gondois]

Hello Sudeep,
Thanks for the patch. Just to add a note, it means that the firmware must have
freq and level values such as:
- freq = K * level
- K >= 1
- K being an integer

If K is not an integer, the bigger K is, the lower the imprecision in the
available frequencies is. Having imprecise frequency values did not impact
the frequency changes when I tried it.

Reviewed-by: Pierre Gondois <pierre.gondois at arm.com>

On 1/19/24 12:10, Sudeep Holla wrote:
> When (sustained_freq_khz * 1000) is less than sustained_perf_level, the
> multiplier will be less than 1 and hence rounded down as 0. Similarly if
> it is not multiple of sustained_perf_level the dom_info->mult_factor will
> contain rounded down value and will end up impacting all the frequency
> calculations done using it.
> 
> Add warning if and when the domain frequency multiplier is 0 or rounded
> down so that it gives a clue to get the firmware tables fixed.
> 
> Suggested-by: Pierre Gondois <Pierre.Gondois at arm.com>
> Cc: Cristian Marussi <cristian.marussi at arm.com>
> Signed-off-by: Sudeep Holla <sudeep.holla at arm.com>
> ---
>   drivers/firmware/arm_scmi/perf.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
> index 8ea2a7b3d35d..5a7358e89d6f 100644
> --- a/drivers/firmware/arm_scmi/perf.c
> +++ b/drivers/firmware/arm_scmi/perf.c
> @@ -272,13 +272,21 @@ scmi_perf_domain_attributes_get(const struct scmi_protocol_handle *ph,
>   					le32_to_cpu(attr->sustained_perf_level);
>   		if (!dom_info->sustained_freq_khz ||
>   		    !dom_info->sustained_perf_level ||
> -		    dom_info->level_indexing_mode)
> +		    dom_info->level_indexing_mode) {
>   			/* CPUFreq converts to kHz, hence default 1000 */
>   			dom_info->mult_factor =	1000;
> -		else
> +		} else {
>   			dom_info->mult_factor =
>   					(dom_info->sustained_freq_khz * 1000UL)
>   					/ dom_info->sustained_perf_level;
> +			if ((dom_info->sustained_freq_khz * 1000UL) %
> +			    dom_info->sustained_perf_level)
> +				pr_warn("mult_factor of domain %d is rounded\n",
> +					dom_info->id);
> +		}
> +		if (!dom_info->mult_factor)
> +			pr_warn("Incorrect sustained perf level or freq kHz\n");
> +
>   		strscpy(dom_info->info.name, attr->name,
>   			SCMI_SHORT_NAME_MAX_SIZE);
>   	}