linux-kernel - [PATCH] phy: qcom-snps: Fixed order of enabling regulators

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Date: Wed, 21 Feb 2024 16:02:02 +0530
From: Krishna Kurapati <quic_kriskura@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        "Kishon Vijay
 Abraham I" <kishon@...nel.org>
CC: <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-phy@...ts.infradead.org>, <quic_ppratap@...cinc.com>,
        <quic_jackp@...cinc.com>, Krishna Kurapati <quic_kriskura@...cinc.com>
Subject: [PATCH] phy: qcom-snps: Fixed order of enabling regulators

The SNPS Femto phy has 3 supplies, vdda-pll (0.88V), vdd18 (1.8V),
vdd33 (3.3V). The driver enables these in order of 0.88 -> 3.3 -> 1.88.
But on phy instances which have EUD attached, it is seen that not enabling
the regulators in the order of (0.88 -> 1.8V -> 3.3V) is causing the EUD to
reset the phy (issue seen rarely) thereby disturbing enumeration.

This change doesn't disturb operation of phy's where EUD is not present.
According to the some of the applicable power-supply ramp scenarios present
in data book: (DVDD is 0.88V, VDDH is 1.8V)

a) VDDH<#> and VDD33<#> held to 0 V (cannot be left floating) with DVDD
ramped to a valid level
b) VDD33<#> held to 0 V (cannot be left floating) with DVDD and VDDH<#>
ramped to their respective, valid levels

Modify the driver to power up the phy regulators in order of:
0.88 -> 1.8 -> 3.3 respectively.

Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
---

Downstream kernels on QC targets use this sequence to power up
the phy and this has been tested extensively on multiple targets.
This change has been tested with upstream kernel on QCM6490-IDP
without EUD to ensure there is no loss or breakage of functionality.

 drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c b/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
index eb0b0f61d98e..e86d221b7397 100644
--- a/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
+++ b/drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c
@@ -79,7 +79,7 @@
 #define LS_FS_OUTPUT_IMPEDANCE_MASK		GENMASK(3, 0)

 static const char * const qcom_snps_hsphy_vreg_names[] = {
-	"vdda-pll", "vdda33", "vdda18",
+	"vdda-pll", "vdda18", "vdda33",
 };

 #define SNPS_HS_NUM_VREGS		ARRAY_SIZE(qcom_snps_hsphy_vreg_names)
-- 
2.34.1