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From:   Avri Altman <Avri.Altman@wdc.com>
To:     Stanley Chu <stanley.chu@mediatek.com>,
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Subject: RE: [PATCH v2 1/5] scsi: ufs-mediatek: Fix imprecise waiting time for
 ref-clk control
Thread-Topic: [PATCH v2 1/5] scsi: ufs-mediatek: Fix imprecise waiting time
 for ref-clk control
Thread-Index: AQHWNZrO/+hW/sT/fkuA3Q4XuyNplKjByVwQ
Date:   Sun, 31 May 2020 07:10:23 +0000
Message-ID: <SN6PR04MB464015BDF84DF7A9779BEB41FC8D0@SN6PR04MB4640.namprd04.prod.outlook.com>
References: <20200529092310.1106-1-stanley.chu@mediatek.com>
 <20200529092310.1106-2-stanley.chu@mediatek.com>
In-Reply-To: <20200529092310.1106-2-stanley.chu@mediatek.com>
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=20
>=20
> Currently ref-clk control timeout is implemented by Jiffies. However
> jiffies is not accurate enough thus "false timeout" may happen.
>=20
> Use more accurate delay mechanism instead, for example, ktime.
>=20
> Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
> Reviewed-by: Andy Teng <andy.teng@mediatek.com>
Reviewed-by: Avri Altman <avri.altman@wdc.com>

> ---
>  drivers/scsi/ufs/ufs-mediatek.c | 7 ++++---
>  drivers/scsi/ufs/ufs-mediatek.h | 2 +-
>  2 files changed, 5 insertions(+), 4 deletions(-)
>=20
> diff --git a/drivers/scsi/ufs/ufs-mediatek.c b/drivers/scsi/ufs/ufs-media=
tek.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 =3D ufshcd_get_variant(hba);
>         struct arm_smccc_res res;
> -       unsigned long timeout;
> +       ktime_t timeout, time_checked;
>         u32 value;
>=20
>         if (host->ref_clk_enabled =3D=3D on)
> @@ -135,8 +135,9 @@ static int ufs_mtk_setup_ref_clk(struct ufs_hba *hba,
> bool on)
>         }
>=20
>         /* Wait for ack */
> -       timeout =3D jiffies + msecs_to_jiffies(REFCLK_REQ_TIMEOUT_MS);
> +       timeout =3D ktime_add_us(ktime_get(), REFCLK_REQ_TIMEOUT_US);
>         do {
> +               time_checked =3D ktime_get();
>                 value =3D ufshcd_readl(hba, REG_UFS_REFCLK_CTRL);
>=20
>                 /* 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;
>=20
>                 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

>=20
>         dev_err(hba->dev, "missing ack of refclk req, reg: 0x%x\n", value=
);
>=20
> diff --git a/drivers/scsi/ufs/ufs-mediatek.h b/drivers/scsi/ufs/ufs-media=
tek.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)
>=20
> -#define REFCLK_REQ_TIMEOUT_MS       3
> +#define REFCLK_REQ_TIMEOUT_US       3000
>=20
>  /*
>   * Vendor specific pre-defined parameters
> --
> 2.18.0