linux-kernel - Re: [PATCH v1 2/2] scsi: ufs: core: Reduce the sleep before vcc can be powered on

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Message-ID: <c12b15699ad8176760c220100247af15954f30d8.camel@mediatek.com>
Date: Thu, 2 Oct 2025 07:59:22 +0000
From: Peter Wang (王信友) <peter.wang@...iatek.com>
To: "avri.altman@....com" <avri.altman@....com>, "quic_cang@...cinc.com"
	<quic_cang@...cinc.com>, "quic_nitirawa@...cinc.com"
	<quic_nitirawa@...cinc.com>, "quic_nguyenb@...cinc.com"
	<quic_nguyenb@...cinc.com>, "manivannan.sadhasivam@...aro.org"
	<manivannan.sadhasivam@...aro.org>, "bvanassche@....org"
	<bvanassche@....org>, "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>
CC: "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"beanhuo@...ron.com" <beanhuo@...ron.com>, "alim.akhtar@...sung.com"
	<alim.akhtar@...sung.com>, "James.Bottomley@...senPartnership.com"
	<James.Bottomley@...senPartnership.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] scsi: ufs: core: Reduce the sleep before vcc can
 be powered on

On Wed, 2025-10-01 at 13:57 -0700, Bao D. Nguyen wrote:
> 
> After the ufs device vcc is powered off, all the ufs device
> manufacturers require a minimum of 1ms of power-off time before
> vcc can be powered on again. This requirement has been verified
> with all the ufs device manufacturer's datasheets.
> Improve the system resume latency by reducing the required power-off
> time from 5ms to 2ms. The chosen 2ms should include enough
> additional buffer time without being wasteful.
> 
> Signed-off-by: Bao D. Nguyen <quic_nguyenb@...cinc.com>
> ---
>  drivers/ufs/core/ufshcd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 45e509b..83bd731 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -9741,7 +9741,7 @@ static void ufshcd_vreg_set_lpm(struct ufs_hba
> *hba)
>          * All UFS devices require delay after VCC power rail is
> turned-off.
>          */
>         if (vcc_off && hba->vreg_info.vcc)
> -               usleep_range(5000, 5100);
> +               usleep_range(2000, 2100);

Hi Bao,

This delay should be compatible with legacy devices.
The initial value was set to 5ms, does that mean there 
is a device that actually needs 5ms?

Thanks
Peter