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

From: Bjorn Andersson <bjorn.andersson@linaro•org>
To: "Asutosh Das (asd)" <asutoshd@codeaurora•org>
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,
	Stanley Chu <stanley.chu@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, alice.chao@mediatek•com
Subject: Re: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage values
Date: Mon, 30 Nov 2020 17:14:37 -0600	[thread overview]
Message-ID: <X8V83T+Tx6teNLOR@builder.lan> (raw)
In-Reply-To: <568660cd-80e6-1b8f-d426-4614c9159ff4@codeaurora.org>

On Mon 30 Nov 16:51 CST 2020, Asutosh Das (asd) wrote:

> On 11/30/2020 1:16 AM, 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>
> > ---
> >   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")) {
> > 
> 
> Hi Stanley
> 
> Thanks for the patch. Bao (nguyenb) was also working towards something
> similar.
> Would it be possible for you to take into account the scenario in which the
> same platform supports both 2.x and 3.x UFS devices?
> 
> These've different voltage requirements, 2.4v-3.6v.
> I'm not sure if standard dts regulator properties can support this.
> 

What is the actual voltage requirement for these devices and how does
the software know what voltage to pick in this range?

Regards,
Bjorn

> -asd
> 
> 
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> Linux Foundation Collaborative Project

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