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

Bjorn Andersson
2021-01-14T17:58:50Z

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@somainline.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
>