linux-kernel - RE: [PATCH v2 1/5] scsi: ufs-mediatek: Fix imprecise waiting time for ref-clk control

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Message-ID: <SN6PR04MB464015BDF84DF7A9779BEB41FC8D0@SN6PR04MB4640.namprd04.prod.outlook.com>
Date:   Sun, 31 May 2020 07:10:23 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     Stanley Chu <stanley.chu@...iatek.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>
CC:     "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "bvanassche@....org" <bvanassche@....org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuohong.wang@...iatek.com" <kuohong.wang@...iatek.com>,
        "peter.wang@...iatek.com" <peter.wang@...iatek.com>,
        "chun-hung.wu@...iatek.com" <chun-hung.wu@...iatek.com>,
        "andy.teng@...iatek.com" <andy.teng@...iatek.com>,
        "cc.chou@...iatek.com" <cc.chou@...iatek.com>,
        "chaotian.jing@...iatek.com" <chaotian.jing@...iatek.com>,
        "pengshun.zhao@...iatek.com" <pengshun.zhao@...iatek.com>
Subject: RE: [PATCH v2 1/5] scsi: ufs-mediatek: Fix imprecise waiting time for
 ref-clk control

 
> 
> Currently ref-clk control timeout is implemented by Jiffies. However
> jiffies is not accurate enough thus "false timeout" may happen.
> 
> Use more accurate delay mechanism instead, for example, ktime.
> 
> Signed-off-by: Stanley Chu <stanley.chu@...iatek.com>
> Reviewed-by: Andy Teng <andy.teng@...iatek.com>
Reviewed-by: Avri Altman <avri.altman@....com>

> ---
>  drivers/scsi/ufs/ufs-mediatek.c | 7 ++++---
>  drivers/scsi/ufs/ufs-mediatek.h | 2 +-
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufs-mediatek.c b/drivers/scsi/ufs/ufs-mediatek.c
> index d56ce8d97d4e..523ee5573921 100644
> --- a/drivers/scsi/ufs/ufs-mediatek.c
> +++ b/drivers/scsi/ufs/ufs-mediatek.c
> @@ -120,7 +120,7 @@ static int ufs_mtk_setup_ref_clk(struct ufs_hba *hba,
> bool on)
>  {
>         struct ufs_mtk_host *host = ufshcd_get_variant(hba);
>         struct arm_smccc_res res;
> -       unsigned long timeout;
> +       ktime_t timeout, time_checked;
>         u32 value;
> 
>         if (host->ref_clk_enabled == on)
> @@ -135,8 +135,9 @@ static int ufs_mtk_setup_ref_clk(struct ufs_hba *hba,
> bool on)
>         }
> 
>         /* Wait for ack */
> -       timeout = jiffies + msecs_to_jiffies(REFCLK_REQ_TIMEOUT_MS);
> +       timeout = ktime_add_us(ktime_get(), REFCLK_REQ_TIMEOUT_US);
>         do {
> +               time_checked = ktime_get();
>                 value = ufshcd_readl(hba, REG_UFS_REFCLK_CTRL);
> 
>                 /* Wait until ack bit equals to req bit */
> @@ -144,7 +145,7 @@ static int ufs_mtk_setup_ref_clk(struct ufs_hba *hba,
> bool on)
>                         goto out;
> 
>                 usleep_range(100, 200);
> -       } while (time_before(jiffies, timeout));
> +       } while (ktime_before(time_checked, timeout));
Nit: you could get rid of time_checked if you would use ktime_compare(ktime_get(), timeout) > 0

Thanks,
Avri

> 
>         dev_err(hba->dev, "missing ack of refclk req, reg: 0x%x\n", value);
> 
> diff --git a/drivers/scsi/ufs/ufs-mediatek.h b/drivers/scsi/ufs/ufs-mediatek.h
> index 5bbd3e9cbae2..fc42dcbfd800 100644
> --- a/drivers/scsi/ufs/ufs-mediatek.h
> +++ b/drivers/scsi/ufs/ufs-mediatek.h
> @@ -28,7 +28,7 @@
>  #define REFCLK_REQUEST              BIT(0)
>  #define REFCLK_ACK                  BIT(1)
> 
> -#define REFCLK_REQ_TIMEOUT_MS       3
> +#define REFCLK_REQ_TIMEOUT_US       3000
> 
>  /*
>   * Vendor specific pre-defined parameters
> --
> 2.18.0