Re: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage values

From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Stanley Chu <stanley.chu@mediatek.com>
Cc: nguyenb@codeaurora.org, matthias.bgg@gmail.com,
	cang@codeaurora.org, alim.akhtar@samsung.com, beanhuo@micron.com,
	bvanassche@acm.org, linux-scsi@vger.kernel.org,
	peter.wang@mediatek.com, cc.chou@mediatek.com,
	andy.teng@mediatek.com, jejb@linux.ibm.com,
	chun-hung.wu@mediatek.com, avri.altman@wdc.com,
	linux-mediatek@lists.infradead.org, jiajie.hao@mediatek.com,
	chaotian.jing@mediatek.com, linux-arm-kernel@lists.infradead.org,
	martin.petersen@oracle.com, kuohong.wang@mediatek.com,
	linux-kernel@vger.kernel.org, asutoshd@codeaurora.org,
	alice.chao@mediatek.com
Subject: Re: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage values
Date: Mon, 30 Nov 2020 17:09:32 -0600	[thread overview]
Message-ID: <X8V7rM6GJd2IOo1f@builder.lan> (raw)
In-Reply-To: <20201130091610.2752-1-stanley.chu@mediatek.com>

On Mon 30 Nov 03:16 CST 2020, Stanley Chu wrote:

> UFS specficication allows different VCC configurations for UFS devices,
> for example,
> 	(1). 2.70V - 3.60V (By default)
> 	(2). 1.70V - 1.95V (Activated if "vcc-supply-1p8" is declared in
>                           device tree)
> 	(3). 2.40V - 2.70V (Supported since UFS 3.x)
> 
> With the introduction of UFS 3.x products, an issue is happening that
> UFS driver will use wrong "min_uV/max_uV" configuration to toggle VCC
> regulator on UFU 3.x products with VCC configuration (3) used.
> 
> To solve this issue, we simply remove pre-defined initial VCC voltage
> values in UFS driver with below reasons,
> 
> 1. UFS specifications do not define how to detect the VCC configuration
>    supported by attached device.
> 
> 2. Device tree already supports standard regulator properties.
> 
> Therefore VCC voltage shall be defined correctly in device tree, and
> shall not be changed by UFS driver. What UFS driver needs to do is simply
> enabling or disabling the VCC regulator only.
> 
> This is a RFC conceptional patch. Please help review this and feel
> free to feedback any ideas. Once this concept is accepted, and then
> I would post a more completed patch series to fix this issue.
> 
> Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

This is the correct thing to do and I would prefer that we did the same
for vccq and vccq2 as well - and thereby remove the min_uV and max_uV
from ufs_vreg.

Regards,
Bjorn

> ---
>  drivers/scsi/ufs/ufshcd-pltfrm.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd-pltfrm.c b/drivers/scsi/ufs/ufshcd-pltfrm.c
> index a6f76399b3ae..3965be03c136 100644
> --- a/drivers/scsi/ufs/ufshcd-pltfrm.c
> +++ b/drivers/scsi/ufs/ufshcd-pltfrm.c
> @@ -133,15 +133,7 @@ static int ufshcd_populate_vreg(struct device *dev, const char *name,
>  		vreg->max_uA = 0;
>  	}
>  
> -	if (!strcmp(name, "vcc")) {
> -		if (of_property_read_bool(np, "vcc-supply-1p8")) {
> -			vreg->min_uV = UFS_VREG_VCC_1P8_MIN_UV;
> -			vreg->max_uV = UFS_VREG_VCC_1P8_MAX_UV;
> -		} else {
> -			vreg->min_uV = UFS_VREG_VCC_MIN_UV;
> -			vreg->max_uV = UFS_VREG_VCC_MAX_UV;
> -		}
> -	} else if (!strcmp(name, "vccq")) {
> +	if (!strcmp(name, "vccq")) {
>  		vreg->min_uV = UFS_VREG_VCCQ_MIN_UV;
>  		vreg->max_uV = UFS_VREG_VCCQ_MAX_UV;
>  	} else if (!strcmp(name, "vccq2")) {
> -- 
> 2.18.0
> 

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