linux-kernel - Re: [PATCH v2 2/3] i2c: qup: Introduce SCL/SDA noise rejection

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Message-ID: <YACGBnAbHllCdGNw@builder.lan>
Date:   Thu, 14 Jan 2021 11:57:26 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Cc:     agross@...nel.org, linux-kernel@...r.kernel.org,
        konrad.dybcio@...ainline.org, marijn.suijten@...ainline.org,
        martin.botka@...ainline.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
Subject: Re: [PATCH v2 2/3] i2c: qup: Introduce SCL/SDA noise rejection

On Thu 14 Jan 11:49 CST 2021, AngeloGioacchino Del Regno wrote:

> 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.
> 

This looks reasonable, just some small nits below.

> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
> ---
>  drivers/i2c/busses/i2c-qup.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
> index 5a47915869ae..af51234a60ba 100644
> --- a/drivers/i2c/busses/i2c-qup.c
> +++ b/drivers/i2c/busses/i2c-qup.c
> @@ -8,6 +8,7 @@
>  #include <linux/acpi.h>
>  #include <linux/atomic.h>
>  #include <linux/clk.h>
> +#include <linux/bitfield.h>

If you move this one step up you'll maintain the sort order.

>  #include <linux/delay.h>
>  #include <linux/dmaengine.h>
>  #include <linux/dmapool.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 = 0, noise_reject_sda = 0;

You shouldn't need to initialize these, device_property_read_u32() won't
return 0 without updating them.

>  	int blocks;
>  	bool is_qup_v1;
>  
> @@ -1860,6 +1864,19 @@ 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);

I would prefer if you didn't break this line.

> +
> +	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);

Ditto.

Regards,
Bjorn

> +
>  	/*
>  	 * 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
>