linux-kernel - Re: [PATCH v4 6/6] media: mt9m114: Set pad-slew-rate

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Message-ID: <20250423182332.GE2675@pendragon.ideasonboard.com>
Date: Wed, 23 Apr 2025 21:23:32 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Mathis Foerst <mathis.foerst@...com>
Cc: linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	linux-media@...r.kernel.org, devicetree@...r.kernel.org,
	manuel.traut@...com, mathis.foerst@...hlke.com
Subject: Re: [PATCH v4 6/6] media: mt9m114: Set pad-slew-rate

Hi Mathis,

Thank you for the patch.

On Fri, Mar 07, 2025 at 10:31:40AM +0100, Mathis Foerst wrote:
> The MT9M114 supports the different slew rates (0 to 7) on the output pads.
> At the moment, this is hardcoded to 7 (the fastest rate).
> The user might want to change this values due to EMC requirements.
> 
> Read the 'slew-rate' from the DT and configure the pad slew rates of
> the output pads accordingly in mt9m114_initialize().
> Remove the hardcoded slew rate setting from the mt9m114_init table.
> 
> Signed-off-by: Mathis Foerst <mathis.foerst@...com>
> ---
>  drivers/media/i2c/mt9m114.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/i2c/mt9m114.c b/drivers/media/i2c/mt9m114.c
> index 79c97ab19be9..fce24c587782 100644
> --- a/drivers/media/i2c/mt9m114.c
> +++ b/drivers/media/i2c/mt9m114.c
> @@ -42,6 +42,9 @@
>  #define MT9M114_RESET_AND_MISC_CONTROL			CCI_REG16(0x001a)
>  #define MT9M114_RESET_SOC					BIT(0)
>  #define MT9M114_PAD_SLEW				CCI_REG16(0x001e)
> +#define MT9M114_PAD_SLEW_MIN					0x00
> +#define MT9M114_PAD_SLEW_MAX					0x07
> +#define MT9M114_PAD_SLEW_DEFAULT				0x07

You can use decimal values here.

>  #define MT9M114_PAD_CONTROL				CCI_REG16(0x0032)
>  
>  /* XDMA registers */
> @@ -388,6 +391,7 @@ struct mt9m114 {
>  
>  	unsigned int pixrate;
>  	bool streaming;
> +	u32 pad_slew_rate;
>  
>  	/* Pixel Array */
>  	struct {
> @@ -645,9 +649,6 @@ static const struct cci_reg_sequence mt9m114_init[] = {
>  	{ MT9M114_CAM_SENSOR_CFG_FINE_INTEG_TIME_MAX,	1459 },
>  	{ MT9M114_CAM_SENSOR_CFG_FINE_CORRECTION,	96 },
>  	{ MT9M114_CAM_SENSOR_CFG_REG_0_DATA,		32 },
> -
> -	/* Miscellaneous settings */
> -	{ MT9M114_PAD_SLEW,				0x0777 },
>  };
>  
>  /* -----------------------------------------------------------------------------
> @@ -778,6 +779,13 @@ static int mt9m114_initialize(struct mt9m114 *sensor)
>  	if (ret < 0)
>  		return ret;
>  
> +	value = (sensor->pad_slew_rate & 0xF)
> +	      | (sensor->pad_slew_rate & 0xF) << 4
> +	      |	(sensor->pad_slew_rate & 0xF) << 8;

No need for ' & 0xF' as you've ensured the slew rate value is in the
valid [0, 7] range.

> +	cci_write(sensor->regmap, MT9M114_PAD_SLEW, value, &ret);
> +	if (ret < 0)
> +		return ret;
> +
>  	ret = mt9m114_set_state(sensor, MT9M114_SYS_STATE_ENTER_CONFIG_CHANGE);
>  	if (ret < 0)
>  		return ret;
> @@ -2357,6 +2365,8 @@ static int mt9m114_parse_dt(struct mt9m114 *sensor)
>  {
>  	struct fwnode_handle *fwnode = dev_fwnode(&sensor->client->dev);
>  	struct fwnode_handle *ep;
> +	struct device_node *dev_node = sensor->client->dev.of_node;
> +	u32 slew_rate;
>  	int ret;
>  
>  	ep = fwnode_graph_get_next_endpoint(fwnode, NULL);
> @@ -2385,6 +2395,11 @@ static int mt9m114_parse_dt(struct mt9m114 *sensor)
>  		goto error;
>  	}
>  
> +	ret = of_property_read_u32(dev_node, "slew-rate", &slew_rate);

Direct usage of OF functions is discouraged. Use
device_property_read_u32() instead, which abstracts the firmware backend
(OF, ACPI, ...). Don't forget to include linux/property.h.

> +	if (ret || slew_rate < MT9M114_PAD_SLEW_MIN || slew_rate > MT9M114_PAD_SLEW_MAX)
> +		slew_rate = MT9M114_PAD_SLEW_DEFAULT;

If the value is erroneous, it indicates the DT is incorrect. I'd log a
message and return an error. As the DT property is optional, you can do
something like

	sensor->slew_rate = MT9M114_PAD_SLEW_DEFAULT;
	device_property_read_u32(&sensor->client.dev, "slew-rate",
				 &sensor->slew_rate);

	if (sensor->slew_rate < MT9M114_PAD_SLEW_MIN ||
	    sensor->slew_rate > MT9M114_PAD_SLEW_MAX) {
	    	dev_err(&sensor->client.dev, "Invalid slew-rate %u\n",
			sensor->slew_rate);
		return -EINVAL;
	}

With this,

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> +	sensor->pad_slew_rate = slew_rate;
> +
>  	return 0;
>  
>  error:

-- 
Regards,

Laurent Pinchart