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

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Message-ID: <20201130091610.2752-1-stanley.chu@mediatek.com>
Date:   Mon, 30 Nov 2020 17:16:10 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     <linux-scsi@...r.kernel.org>, <martin.petersen@...cle.com>,
        <avri.altman@....com>, <alim.akhtar@...sung.com>,
        <jejb@...ux.ibm.com>
CC:     <beanhuo@...ron.com>, <asutoshd@...eaurora.org>,
        <cang@...eaurora.org>, <matthias.bgg@...il.com>,
        <bvanassche@....org>, <linux-mediatek@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <nguyenb@...eaurora.org>,
        <bjorn.andersson@...aro.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>, <jiajie.hao@...iatek.com>,
        <alice.chao@...iatek.com>, Stanley Chu <stanley.chu@...iatek.com>
Subject: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage values

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@...iatek.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")) {
-- 
2.18.0