[PATCH] i2c: imx: Implement errata ERR007805 or e7805 bus frequency limit

[Marek Vasut]

The i.MX8MP Mask Set Errata for Mask 1P33A, Rev. 2.0 has description of
errata ERR007805 as below. This errata is found on all MX8M{M,N,P,Q},
MX7{S,D}, MX6{UL{,L,Z},S{,LL,X},S,D,DL,Q,DP,QP} . MX7ULP, MX8Q, MX8X
are not affected. MX53 and older status is unknown, as the errata
first appears in MX6 errata sheets from 2016 and the latest errata
sheet for MX53 is from 2015. Older SoC errata sheets predate the
MX53 errata sheet. MX8ULP and MX9 status is unknown as the errata
sheet is not available yet.

"
ERR007805 I2C: When the I2C clock speed is configured for 400 kHz,
the SCL low period violates the I2C spec of 1.3 uS min

Description: When the I2C module is programmed to operate at the
maximum clock speed of 400 kHz (as defined by the I2C spec), the SCL
clock low period violates the I2C spec of 1.3 uS min. The user must
reduce the clock speed to obtain the SCL low time to meet the 1.3us
I2C minimum required. This behavior means the SoC is not compliant
to the I2C spec at 400kHz.

Workaround: To meet the clock low period requirement in fast speed
mode, SCL must be configured to 384KHz or less.
"

Implement the workaround by matching on the affected SoC specific
compatible strings and by limiting the maximum bus frequency in case
the SoC is affected.

Signed-off-by: Marek Vasut <marex at denx.de>
Cc: Fabio Estevam <festevam at denx.de>
Cc: Francesco Dolcini <francesco.dolcini at toradex.com>
Cc: Marcel Ziswiler <marcel.ziswiler at toradex.com>
Cc: Oleksij Rempel <linux at rempel-privat.de>
Cc: Peng Fan <peng.fan at nxp.com>
Cc: Shawn Guo <shawnguo at kernel.org>
Cc: NXP Linux Team <linux-imx at nxp.com>
Cc: linux-arm-kernel at lists.infradead.org
To: linux-i2c at vger.kernel.org
---
 drivers/i2c/busses/i2c-imx.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 27f969b3dc072..e9e2db68b9fb6 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -179,6 +179,12 @@ struct imx_i2c_hwdata {
 	unsigned int		ndivs;
 	unsigned int		i2sr_clr_opcode;
 	unsigned int		i2cr_ien_opcode;
+	/*
+	 * Errata ERR007805 or e7805:
+	 * I2C: When the I2C clock speed is configured for 400 kHz,
+	 * the SCL low period violates the I2C spec of 1.3 uS min.
+	 */
+	bool			has_err007805;
 };
 
 struct imx_i2c_dma {
@@ -240,6 +246,16 @@ static const struct imx_i2c_hwdata imx21_i2c_hwdata = {
 
 };
 
+static const struct imx_i2c_hwdata imx6_i2c_hwdata = {
+	.devtype		= IMX21_I2C,
+	.regshift		= IMX_I2C_REGSHIFT,
+	.clk_div		= imx_i2c_clk_div,
+	.ndivs			= ARRAY_SIZE(imx_i2c_clk_div),
+	.i2sr_clr_opcode	= I2SR_CLR_OPCODE_W0C,
+	.i2cr_ien_opcode	= I2CR_IEN_OPCODE_1,
+	.has_err007805		= true,
+};
+
 static struct imx_i2c_hwdata vf610_i2c_hwdata = {
 	.devtype		= VF610_I2C,
 	.regshift		= VF610_I2C_REGSHIFT,
@@ -266,6 +282,16 @@ MODULE_DEVICE_TABLE(platform, imx_i2c_devtype);
 static const struct of_device_id i2c_imx_dt_ids[] = {
 	{ .compatible = "fsl,imx1-i2c", .data = &imx1_i2c_hwdata, },
 	{ .compatible = "fsl,imx21-i2c", .data = &imx21_i2c_hwdata, },
+	{ .compatible = "fsl,imx6q-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx6sl-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx6sll-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx6sx-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx6ul-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx7s-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx8mm-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx8mn-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx8mp-i2c", .data = &imx6_i2c_hwdata, },
+	{ .compatible = "fsl,imx8mq-i2c", .data = &imx6_i2c_hwdata, },
 	{ .compatible = "fsl,vf610-i2c", .data = &vf610_i2c_hwdata, },
 	{ /* sentinel */ }
 };
@@ -551,6 +577,13 @@ static void i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx,
 	unsigned int div;
 	int i;
 
+	if (i2c_imx->hwdata->has_err007805 && i2c_imx->bitrate > 384000) {
+		dev_dbg(&i2c_imx->adapter.dev,
+			"SoC errata ERR007805 or e7805 applies, bus frequency limited from %d Hz to 384000 Hz.\n",
+			i2c_imx->bitrate);
+		i2c_imx->bitrate = 384000;
+	}
+
 	/* Divider value calculation */
 	if (i2c_imx->cur_clk == i2c_clk_rate)
 		return;
-- 
2.35.1