linux-kernel - [PATCH 3.2 028/126] regulator: tps65910: Work around silicon erratum SWCZ010

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Message-ID: <lsq.1487198494.295324235@decadent.org.uk>
Date:   Wed, 15 Feb 2017 22:41:34 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Mark Brown" <broonie@...nel.org>,
        "Jan Remmet" <j.remmet@...tec.de>
Subject: [PATCH 3.2 028/126] regulator: tps65910: Work around silicon
 erratum SWCZ010

3.2.85-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Remmet <j.remmet@...tec.de>

commit 8f9165c981fed187bb483de84caf9adf835aefda upstream.

http://www.ti.com/lit/pdf/SWCZ010:
  DCDC o/p voltage can go higher than programmed value

Impact:
VDDI, VDD2, and VIO output programmed voltage level can go higher than
expected or crash, when coming out of PFM to PWM mode or using DVFS.

Description:
When DCDC CLK SYNC bits are 11/01:
* VIO 3-MHz oscillator is the source clock of the digital core and input
  clock of VDD1 and VDD2
* Turn-on of VDD1 and VDD2 HSD PFETis synchronized or at a constant
  phase shift
* Current pulled though VCC1+VCC2 is Iload(VDD1) + Iload(VDD2)
* The 3 HSD PFET will be turned-on at the same time, causing the highest
  possible switching noise on the application. This noise level depends
  on the layout, the VBAT level, and the load current. The noise level
  increases with improper layout.

When DCDC CLK SYNC bits are 00:
* VIO 3-MHz oscillator is the source clock of digital core
* VDD1 and VDD2 are running on their own 3-MHz oscillator
* Current pulled though VCC1+VCC2 average of Iload(VDD1) + Iload(VDD2)
* The switching noise of the 3 SMPS will be randomly spread over time,
  causing lower overall switching noise.

Workaround:
Set DCDCCTRL_REG[1:0]= 00.

Signed-off-by: Jan Remmet <j.remmet@...tec.de>
Signed-off-by: Mark Brown <broonie@...nel.org>
[bwh: Backported to 3.2: use tps65910_clear_bits()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/regulator/tps65910-regulator.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/regulator/tps65910-regulator.c
+++ b/drivers/regulator/tps65910-regulator.c
@@ -904,6 +904,12 @@ static __devinit int tps65910_probe(stru
 		pmic->get_ctrl_reg = &tps65910_get_ctrl_register;
 		pmic->num_regulators = ARRAY_SIZE(tps65910_regs);
 		info = tps65910_regs;
+		/* Work around silicon erratum SWCZ010: output programmed
+		 * voltage level can go higher than expected or crash
+		 * Workaround: use no synchronization of DCDC clocks
+		 */
+		tps65910_clear_bits(pmic->mfd, TPS65910_DCDCCTRL,
+				    DCDCCTRL_DCDCCKSYNC_MASK);
 		break;
 	case TPS65911:
 		pmic->get_ctrl_reg = &tps65911_get_ctrl_register;