linux-kernel - [PATCH 6/6] mfd: iqs62x: Do not change clock frequency during ATI

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Date:   Sun,  3 Jan 2021 14:56:09 -0600
From:   Jeff LaBundy <jeff@...undy.com>
To:     lee.jones@...aro.org
Cc:     linux-kernel@...r.kernel.org, Jeff LaBundy <jeff@...undy.com>
Subject: [PATCH 6/6] mfd: iqs62x: Do not change clock frequency during ATI

After a reset event, the device automatically triggers ATI at the
default core clock frequency (16 MHz). Soon afterward, the driver
loads firmware which may attempt to lower the frequency.

If this initial ATI cycle is still in progress when the frequency
is changed, however, the device incorrectly reports channels 0, 1
and 2 to be in a state of touch once ATI finally completes.

To solve this problem, wait until ATI is complete before lowering
the frequency. Because this particular ATI cycle occurs following
a reset event, its duration is predictable and a simple delay can
suffice.

Signed-off-by: Jeff LaBundy <jeff@...undy.com>
---
 drivers/mfd/iqs62x.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/mfd/iqs62x.c b/drivers/mfd/iqs62x.c
index 9fdf32f..3b32542 100644
--- a/drivers/mfd/iqs62x.c
+++ b/drivers/mfd/iqs62x.c
@@ -81,6 +81,7 @@
 #define IQS62X_FW_REC_TYPE_MASK			3
 #define IQS62X_FW_REC_TYPE_DATA			4

+#define IQS62X_ATI_STARTUP_MS			350
 #define IQS62X_FILT_SETTLE_MS			250

 struct iqs62x_fw_rec {
@@ -111,6 +112,14 @@ static int iqs62x_dev_init(struct iqs62x_core *iqs62x)
 	int ret;

 	list_for_each_entry(fw_blk, &iqs62x->fw_blk_head, list) {
+		/*
+		 * In case ATI is in progress, wait for it to complete before
+		 * lowering the core clock frequency.
+		 */
+		if (fw_blk->addr == IQS62X_SYS_SETTINGS &&
+		    *fw_blk->data & IQS62X_SYS_SETTINGS_CLK_DIV)
+			msleep(IQS62X_ATI_STARTUP_MS);
+
 		if (fw_blk->mask)
 			ret = regmap_update_bits(iqs62x->regmap, fw_blk->addr,
 						 fw_blk->mask, *fw_blk->data);
-- 
2.7.4