linux-kernel - Re: [PATCH v1 1/2] scsi: ufs: Introduce device quirk "DELAY_AFTER

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Date:   Wed, 29 Jul 2020 13:31:40 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
Cc:     linux-scsi@...r.kernel.org, martin.petersen@...cle.com,
        avri.altman@....com, alim.akhtar@...sung.com, jejb@...ux.ibm.com,
        beanhuo@...ron.com, asutoshd@...eaurora.org,
        matthias.bgg@...il.com, bvanassche@....org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kuohong.wang@...iatek.com, peter.wang@...iatek.com,
        chun-hung.wu@...iatek.com, andy.teng@...iatek.com,
        chaotian.jing@...iatek.com, cc.chou@...iatek.com
Subject: Re: [PATCH v1 1/2] scsi: ufs: Introduce device quirk
 "DELAY_AFTER_LPM"

Hi Stanley,

On 2020-07-29 13:18, Stanley Chu wrote:
> Some UFS devices require delay after VCC power rail is turned-off.
> Introduce a device quirk "DELAY_AFTER_LPM" to add 5ms delays after
> VCC power-off during suspend flow.
> 

Just curious, I can understand if you want to add some delays before
turnning off VCC/VCCQ/VCCQ2, but what is the delay AFTER turnning
them off for? I mean the power has been cut by host from PMIC, how
can the delay benefit the UFS device?

Thanks,

Can Guo.

> Signed-off-by: Andy Teng <andy.teng@...iatek.com>
> Signed-off-by: Peter Wang <peter.wang@...iatek.com>
> Signed-off-by: Stanley Chu <stanley.chu@...iatek.com>
> ---
>  drivers/scsi/ufs/ufs_quirks.h |  7 +++++++
>  drivers/scsi/ufs/ufshcd.c     | 11 +++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/scsi/ufs/ufs_quirks.h 
> b/drivers/scsi/ufs/ufs_quirks.h
> index 2a0041493e30..07f559ac5883 100644
> --- a/drivers/scsi/ufs/ufs_quirks.h
> +++ b/drivers/scsi/ufs/ufs_quirks.h
> @@ -109,4 +109,11 @@ struct ufs_dev_fix {
>   */
>  #define UFS_DEVICE_QUIRK_SUPPORT_EXTENDED_FEATURES (1 << 10)
> 
> +/*
> + * Some UFS devices require delay after VCC power rail is turned-off.
> + * Enable this quirk to introduce 5ms delays after VCC power-off 
> during
> + * suspend flow.
> + */
> +#define UFS_DEVICE_QUIRK_DELAY_AFTER_LPM        (1 << 11)
> +
>  #endif /* UFS_QUIRKS_H_ */
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index acba2271c5d3..63f4e2f75aa1 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -8111,6 +8111,8 @@ static int ufshcd_link_state_transition(struct
> ufs_hba *hba,
> 
>  static void ufshcd_vreg_set_lpm(struct ufs_hba *hba)
>  {
> +	bool vcc_off = false;
> +
>  	/*
>  	 * It seems some UFS devices may keep drawing more than sleep current
>  	 * (atleast for 500us) from UFS rails (especially from VCCQ rail).
> @@ -8139,13 +8141,22 @@ static void ufshcd_vreg_set_lpm(struct ufs_hba 
> *hba)
>  	if (ufshcd_is_ufs_dev_poweroff(hba) && ufshcd_is_link_off(hba) &&
>  	    !hba->dev_info.is_lu_power_on_wp) {
>  		ufshcd_setup_vreg(hba, false);
> +		vcc_off = true;
>  	} else if (!ufshcd_is_ufs_dev_active(hba)) {
>  		ufshcd_toggle_vreg(hba->dev, hba->vreg_info.vcc, false);
> +		vcc_off = true;
>  		if (!ufshcd_is_link_active(hba)) {
>  			ufshcd_config_vreg_lpm(hba, hba->vreg_info.vccq);
>  			ufshcd_config_vreg_lpm(hba, hba->vreg_info.vccq2);
>  		}
>  	}
> +
> +	/*
> +	 * Some UFS devices require delay after VCC power rail is turned-off.
> +	 */
> +	if (vcc_off && hba->vreg_info.vcc &&
> +		hba->dev_quirks & UFS_DEVICE_QUIRK_DELAY_AFTER_LPM)
> +		usleep_range(5000, 5100);
>  }
> 
>  static int ufshcd_vreg_set_hpm(struct ufs_hba *hba)