Re: [PATCH v4] ufs: core: fix lockdep warning of clk_scaling_lock

[Bart Van Assche <bvanassche@acm.org>]

On 7/26/22 20:21, peter.wang@mediatek.com wrote:
> -	/* Enable Write Booster if we have scaled up else disable it */
> -	downgrade_write(&hba->clk_scaling_lock);
> -	is_writelock = false;
> -	ufshcd_wb_toggle(hba, scale_up);
> +	/* Disable clk_scaling until ufshcd_wb_toggle finish */
> +	hba->clk_scaling.is_allowed = false;
> +	wb_toggle = true;
>   
>   out_unprepare:
> -	ufshcd_clock_scaling_unprepare(hba, is_writelock);
> +	ufshcd_clock_scaling_unprepare(hba);
> +
> +	/* Enable Write Booster if we have scaled up else disable it */
> +	if (wb_toggle) {
> +		ufshcd_wb_toggle(hba, scale_up);
> +		ufshcd_clk_scaling_allow(hba, true);
> +	}

I'm concerned that briefly disabling clock scaling may cause the clock 
to remain at a high frequency even if it shouldn't. Has the following 
approach been considered? Instead of moving the 
ufshcd_clk_scaling_allow() call, convert dev_cmd.lock into a semaphore, 
lock it near the start of ufshcd_devfreq_scale() and unlock it near the 
end of the same function.

Thanks,

Bart.