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

[Oleksij Rempel <o.rempel@pengutronix.de>]

On Fri, Apr 08, 2022 at 07:15:24PM +0200, Marek Vasut wrote:
> 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@denx.de>
> Cc: Fabio Estevam <festevam@denx.de>
> Cc: Francesco Dolcini <francesco.dolcini@toradex.com>
> Cc: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> Cc: Oleksij Rempel <linux@rempel-privat.de>
> Cc: Peng Fan <peng.fan@nxp.com>
> Cc: Shawn Guo <shawnguo@kernel.org>
> Cc: NXP Linux Team <linux-imx@nxp.com>
> Cc: linux-arm-kernel@lists.infradead.org
> To: linux-i2c@vger.kernel.org

Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>

Thank you!

> ---
>  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
> 
> 
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