linux-kernel - [PATCH v3 2/3] i2c: qup: Introduce SCL/SDA noise rejection

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Date:   Thu, 14 Jan 2021 19:04:14 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
To:     agross@...nel.org
Cc:     linux-kernel@...r.kernel.org, konrad.dybcio@...ainline.org,
        marijn.suijten@...ainline.org, martin.botka@...ainline.org,
        bjorn.andersson@...aro.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-i2c@...r.kernel.org, phone-devel@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Subject: [PATCH v3 2/3] i2c: qup: Introduce SCL/SDA noise rejection

Some I2C devices may be glitchy due to electrical noise coming
from the device itself or because of possible board design issues.
To overcome this issue, the QUP's I2C in Qualcomm SoCs supports
a noise rejection setting for both SCL and SDA lines.

Introduce a setting for noise rejection through device properties,
"qcom,noise-reject-sda" and "qcom,noise-reject-scl", which will
be used to set the level of noise rejection sensitivity.
If the properties are not specified, noise rejection will not be
enabled.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
---
 drivers/i2c/busses/i2c-qup.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
index 5a47915869ae..a01f6f32ba67 100644
--- a/drivers/i2c/busses/i2c-qup.c
+++ b/drivers/i2c/busses/i2c-qup.c
@@ -7,6 +7,7 @@
 
 #include <linux/acpi.h>
 #include <linux/atomic.h>
+#include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/dmaengine.h>
@@ -39,6 +40,8 @@
 #define QUP_MX_READ_CNT		0x208
 #define QUP_IN_FIFO_BASE	0x218
 #define QUP_I2C_CLK_CTL		0x400
+#define  QUP_I2C_CLK_CTL_SDA_NR	GENMASK(27, 26)
+#define  QUP_I2C_CLK_CTL_SCL_NR	GENMASK(25, 24)
 #define QUP_I2C_STATUS		0x404
 #define QUP_I2C_MASTER_GEN	0x408
 
@@ -1663,6 +1666,7 @@ static int qup_i2c_probe(struct platform_device *pdev)
 	int ret, fs_div, hs_div;
 	u32 src_clk_freq = DEFAULT_SRC_CLK;
 	u32 clk_freq = DEFAULT_CLK_FREQ;
+	u32 noise_reject_scl, noise_reject_sda;
 	int blocks;
 	bool is_qup_v1;
 
@@ -1860,6 +1864,17 @@ static int qup_i2c_probe(struct platform_device *pdev)
 		qup->clk_ctl = ((fs_div / 2) << 16) | (hs_div << 8) | (fs_div & 0xff);
 	}
 
+	/* SCL/SDA Noise rejection (optional) */
+	ret = device_property_read_u32(qup->dev, "qcom,noise-reject-scl",
+				      &noise_reject_scl);
+	if (ret == 0)
+		qup->clk_ctl |= FIELD_PREP(QUP_I2C_CLK_CTL_SCL_NR, noise_reject_scl);
+
+	ret = device_property_read_u32(qup->dev, "qcom,noise-reject-sda",
+				      &noise_reject_sda);
+	if (ret == 0)
+		qup->clk_ctl |= FIELD_PREP(QUP_I2C_CLK_CTL_SDA_NR, noise_reject_sda);
+
 	/*
 	 * Time it takes for a byte to be clocked out on the bus.
 	 * Each byte takes 9 clock cycles (8 bits + 1 ack).
-- 
2.29.2