linux-kernel - Re: [PATCH v4 5/5] scsi: ufs: fix clkgating on/off correctly

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Date:   Tue, 27 Oct 2020 10:20:50 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, alim.akhtar@...sung.com,
        avri.altman@....com, bvanassche@....org,
        Asutosh Das <asutoshd@...eaurora.org>
Subject: Re: [PATCH v4 5/5] scsi: ufs: fix clkgating on/off correctly

On 2020-10-27 03:51, Jaegeuk Kim wrote:
> The below call stack prevents clk_gating at every IO completion.
> We can remove the condition, ufshcd_any_tag_in_use(), since 
> clkgating_work
> will check it again.
> 
> ufshcd_complete_requests(struct ufs_hba *hba)
>   ufshcd_transfer_req_compl()
>     __ufshcd_transfer_req_compl()
>       __ufshcd_release(hba)
>         if (ufshcd_any_tag_in_use() == 1)
>            return;
>   ufshcd_tmc_handler(hba);
>     blk_mq_tagset_busy_iter();
> 
> Note that, this still requires a work to deal with a potential racy 
> condition
> when user sets clkgating.delay_ms to very small value. That can cause 
> preventing
> clkgating by the check of ufshcd_any_tag_in_use() in gate_work.
> 
> Fixes: 7252a3603015 ("scsi: ufs: Avoid busy-waiting by eliminating tag
> conflicts")
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> Reviewed-by: Asutosh Das <asutoshd@...eaurora.org>

Reviewed-by: Can Guo <cang@...eaurora.org>

> ---
>  drivers/scsi/ufs/ufshcd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index b8a54d09e750..86c8dee01ca9 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1746,7 +1746,7 @@ static void __ufshcd_release(struct ufs_hba *hba)
> 
>  	if (hba->clk_gating.active_reqs || hba->clk_gating.is_suspended ||
>  	    hba->ufshcd_state != UFSHCD_STATE_OPERATIONAL ||
> -	    ufshcd_any_tag_in_use(hba) || hba->outstanding_tasks ||
> +	    hba->outstanding_tasks ||
>  	    hba->active_uic_cmd || hba->uic_async_done ||
>  	    hba->clk_gating.state == CLKS_OFF)
>  		return;