linux-kernel - Re: [PATCH v7 7/8] scsi: ufs-qcom: Delay specific time before gate ref clk

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Message-ID: <20200206203336.GQ2514@yoga>
Date:   Thu, 6 Feb 2020 12:33:36 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Can Guo <cang@...eaurora.org>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, rnayak@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.com,
        Andy Gross <agross@...nel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 7/8] scsi: ufs-qcom: Delay specific time before gate
 ref clk

On Thu 06 Feb 00:33 PST 2020, Can Guo wrote:

> After enter hibern8, as UFS JEDEC ver 3.0 requires, a specific gating wait
> time is required before disable the device reference clock. If it is not
> specified, use the old delay.
> 
> Signed-off-by: Can Guo <cang@...eaurora.org>
> Reviewed-by: Asutosh Das <asutoshd@...eaurora.org>
> Reviewed-by: Hongwu Su <hongwus@...eaurora.org>
> ---
>  drivers/scsi/ufs/ufs-qcom.c | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufs-qcom.c b/drivers/scsi/ufs/ufs-qcom.c
> index 85d7c17..39eefa4 100644
> --- a/drivers/scsi/ufs/ufs-qcom.c
> +++ b/drivers/scsi/ufs/ufs-qcom.c
> @@ -833,6 +833,8 @@ static int ufs_qcom_bus_register(struct ufs_qcom_host *host)
>  
>  static void ufs_qcom_dev_ref_clk_ctrl(struct ufs_qcom_host *host, bool enable)
>  {
> +	unsigned long gating_wait;
> +
>  	if (host->dev_ref_clk_ctrl_mmio &&
>  	    (enable ^ host->is_dev_ref_clk_enabled)) {
>  		u32 temp = readl_relaxed(host->dev_ref_clk_ctrl_mmio);
> @@ -845,11 +847,25 @@ static void ufs_qcom_dev_ref_clk_ctrl(struct ufs_qcom_host *host, bool enable)
>  		/*
>  		 * If we are here to disable this clock it might be immediately
>  		 * after entering into hibern8 in which case we need to make
> -		 * sure that device ref_clk is active at least 1us after the
> +		 * sure that device ref_clk is active for specific time after
>  		 * hibern8 enter.
>  		 */
> -		if (!enable)
> -			udelay(1);
> +		if (!enable) {
> +			gating_wait = host->hba->dev_info.clk_gating_wait_us;
> +			if (!gating_wait) {

Afaict this can't happen, because in patch 6 you check for gating_wait
being 0 and if so set it to 0xff.

> +				udelay(1);
> +			} else {
> +				/*
> +				 * bRefClkGatingWaitTime defines the minimum
> +				 * time for which the reference clock is
> +				 * required by device during transition from
> +				 * HS-MODE to LS-MODE or HIBERN8 state. Give it
> +				 * more time to be on the safe side.
> +				 */
> +				gating_wait += 10;
> +				usleep_range(gating_wait, gating_wait + 10);

I presume there's no strong requirement on the max, so how about using a
substantially larger max - say 1k, or 10k - to allow the usleep_range()
to do it's job?


PS. Please include linux-arm-msm@ on all the patches in the series, not
just two of them.

Regards,
Bjorn

> +			}
> +		}
>  
>  		writel_relaxed(temp, host->dev_ref_clk_ctrl_mmio);
>  
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project