Re: [PATCH 1/3] media: Add MIPI CCI register access helper functions

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Hans,

Thank you for the patchset.

On Tue, Jun 06, 2023 at 06:58:06PM +0200, Hans de Goede wrote:
> The CSI2 specification specifies a standard method to access camera sensor
> registers called "Camera Control Interface (CCI)".
> 
> This uses either 8 or 16 bit (big-endian wire order) register addresses
> and supports 8, 16, 24 or 32 bit (big-endian wire order) register widths.
> 
> Currently a lot of Linux camera sensor drivers all have their own custom
> helpers for this, often copy and pasted from other drivers.
> 
> Add a set of generic helpers for this so that all sensor drivers can
> switch to a single common implementation.
> 
> These helpers take an extra optional "int *err" function parameter,
> this can be used to chain a bunch of register accesses together with
> only a single error check at the end, rather then needing to error
> check each individual register access. The first failing call will
> set the contents of err to a non 0 value and all other calls will
> then become no-ops.
> 
> Link: https://lore.kernel.org/linux-media/59aefa7f-7bf9-6736-6040-39551329cd0a@redhat.com/
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  Documentation/driver-api/media/v4l2-cci.rst  |   5 +
>  Documentation/driver-api/media/v4l2-core.rst |   1 +
>  drivers/media/v4l2-core/Kconfig              |   5 +
>  drivers/media/v4l2-core/Makefile             |   1 +
>  drivers/media/v4l2-core/v4l2-cci.c           | 142 +++++++++++++++++++
>  include/media/v4l2-cci.h                     | 109 ++++++++++++++
>  6 files changed, 263 insertions(+)
>  create mode 100644 Documentation/driver-api/media/v4l2-cci.rst
>  create mode 100644 drivers/media/v4l2-core/v4l2-cci.c
>  create mode 100644 include/media/v4l2-cci.h
> 
> diff --git a/Documentation/driver-api/media/v4l2-cci.rst b/Documentation/driver-api/media/v4l2-cci.rst
> new file mode 100644
> index 000000000000..dd297a40ed20
> --- /dev/null
> +++ b/Documentation/driver-api/media/v4l2-cci.rst
> @@ -0,0 +1,5 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +V4L2 CCI kAPI
> +^^^^^^^^^^^^^
> +.. kernel-doc:: include/media/v4l2-cci.h
> diff --git a/Documentation/driver-api/media/v4l2-core.rst b/Documentation/driver-api/media/v4l2-core.rst
> index 1a8c4a5f256b..239045ecc8f4 100644
> --- a/Documentation/driver-api/media/v4l2-core.rst
> +++ b/Documentation/driver-api/media/v4l2-core.rst
> @@ -22,6 +22,7 @@ Video4Linux devices
>      v4l2-mem2mem
>      v4l2-async
>      v4l2-fwnode
> +    v4l2-cci
>      v4l2-rect
>      v4l2-tuner
>      v4l2-common
> diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
> index 348559bc2468..523ba243261d 100644
> --- a/drivers/media/v4l2-core/Kconfig
> +++ b/drivers/media/v4l2-core/Kconfig
> @@ -74,6 +74,11 @@ config V4L2_FWNODE
>  config V4L2_ASYNC
>  	tristate
>  
> +config V4L2_CCI
> +	tristate
> +	depends on I2C
> +	select REGMAP_I2C
> +
>  # Used by drivers that need Videobuf modules
>  config VIDEOBUF_GEN
>  	tristate
> diff --git a/drivers/media/v4l2-core/Makefile b/drivers/media/v4l2-core/Makefile
> index 41d91bd10cf2..be2551705755 100644
> --- a/drivers/media/v4l2-core/Makefile
> +++ b/drivers/media/v4l2-core/Makefile
> @@ -25,6 +25,7 @@ videodev-$(CONFIG_VIDEO_V4L2_I2C) += v4l2-i2c.o
>  # (e. g. LC_ALL=C sort Makefile)
>  
>  obj-$(CONFIG_V4L2_ASYNC) += v4l2-async.o
> +obj-$(CONFIG_V4L2_CCI) += v4l2-cci.o
>  obj-$(CONFIG_V4L2_FLASH_LED_CLASS) += v4l2-flash-led-class.o
>  obj-$(CONFIG_V4L2_FWNODE) += v4l2-fwnode.o
>  obj-$(CONFIG_V4L2_H264) += v4l2-h264.o
> diff --git a/drivers/media/v4l2-core/v4l2-cci.c b/drivers/media/v4l2-core/v4l2-cci.c
> new file mode 100644
> index 000000000000..21207d137dbe
> --- /dev/null
> +++ b/drivers/media/v4l2-core/v4l2-cci.c
> @@ -0,0 +1,142 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * MIPI Camera Control Interface (CCI) register access helpers.
> + *
> + * Copyright (C) 2023 Hans de Goede <hansg@kernel.org>
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/dev_printk.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +
> +#include <media/v4l2-cci.h>
> +
> +int cci_read(struct regmap *map, u32 reg, u32 *val, int *err)
> +{
> +	int i, len, ret;

Could i and len be unsigned?

> +	u8 buf[4];
> +
> +	if (err && *err)
> +		return *err;
> +
> +	/* Set len to register width in bytes */
> +	len = ((reg & CCI_REG_WIDTH_MASK) >> CCI_REG_WIDTH_SHIFT) + 1;
> +	reg &= CCI_REG_ADDR_MASK;
> +
> +	ret = regmap_bulk_read(map, reg, buf, len);
> +	if (ret) {
> +		dev_err(regmap_get_device(map), "Error reading reg 0x%4x: %d\n", reg, ret);
> +		if (err)
> +			*err = ret;
> +
> +		return ret;
> +	}
> +
> +	*val = 0;
> +	for (i = 0; i < len; i++) {
> +		*val <<= 8;
> +		*val |= buf[i];
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(cci_read);
> +
> +int cci_write(struct regmap *map, u32 reg, u32 val, int *err)
> +{
> +	int i, len, ret;

Same here.

> +	u8 buf[4];
> +
> +	if (err && *err)
> +		return *err;
> +
> +	/* Set len to register width in bytes */
> +	len = ((reg & CCI_REG_WIDTH_MASK) >> CCI_REG_WIDTH_SHIFT) + 1;
> +	reg &= CCI_REG_ADDR_MASK;
> +
> +	for (i = 0; i < len; i++) {
> +		buf[len - i - 1] = val & 0xff;
> +		val >>= 8;
> +	}
> +
> +	ret = regmap_bulk_write(map, reg, buf, len);
> +	if (ret) {
> +		dev_err(regmap_get_device(map), "Error writing reg 0x%4x: %d\n", reg, ret);
> +		if (err)
> +			*err = ret;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(cci_write);
> +
> +int cci_update_bits(struct regmap *map, u32 reg, u32 mask, u32 val, int *err)
> +{
> +	int width, ret;
> +	u32 readval;
> +
> +	if (err && *err)
> +		return *err;
> +
> +	/*
> +	 * For single byte updates use regmap_update_bits(), this uses
> +	 * the regmap-lock to protect against other read-modify-writes racing.
> +	 */
> +	width = (reg & CCI_REG_WIDTH_MASK) >> CCI_REG_WIDTH_SHIFT;
> +	if (width == cci_reg_8) {
> +		reg &= CCI_REG_ADDR_MASK;
> +		ret = regmap_update_bits(map, reg, mask, val);
> +		if (ret) {
> +			dev_err(regmap_get_device(map), "Error updating reg 0x%4x: %d\n", reg, ret);
> +			if (err)
> +				*err = ret;
> +		}
> +
> +		return ret;
> +	}
> +
> +	ret = cci_read(map, reg, &readval, err);
> +	if (ret)
> +		return ret;
> +
> +	val = (readval & ~mask) | (val & mask);
> +
> +	return cci_write(map, reg, val, err);
> +}
> +EXPORT_SYMBOL_GPL(cci_update_bits);
> +
> +int cci_multi_reg_write(struct regmap *map, const struct reg_sequence *regs, int num_regs, int *err)
> +{
> +	int i, ret;
> +
> +	if (err && *err)
> +		return *err;
> +
> +	for (i = 0; i < num_regs; i++) {
> +		ret = cci_write(map, regs[i].reg, regs[i].def, err);
> +		if (ret)
> +			return ret;
> +
> +		if (regs[i].delay_us)
> +			fsleep(regs[i].delay_us);
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(cci_multi_reg_write);
> +
> +struct regmap *cci_regmap_init_i2c(struct i2c_client *client, int reg_addr_bits)
> +{
> +	struct regmap_config config = {
> +		.reg_bits = reg_addr_bits,
> +		.val_bits = 8,
> +		.reg_format_endian = REGMAP_ENDIAN_BIG,
> +	};
> +
> +	return devm_regmap_init_i2c(client, &config);
> +}
> +EXPORT_SYMBOL_GPL(cci_regmap_init_i2c);

Bulk write functions would be nice, too: CCI does not limit access to
register-like targets.

> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Hans de Goede <hansg@kernel.org>");
> diff --git a/include/media/v4l2-cci.h b/include/media/v4l2-cci.h
> new file mode 100644
> index 000000000000..69b8a7c4a013
> --- /dev/null
> +++ b/include/media/v4l2-cci.h
> @@ -0,0 +1,109 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * MIPI Camera Control Interface (CCI) register access helpers.
> + *
> + * Copyright (C) 2023 Hans de Goede <hansg@kernel.org>
> + */
> +#ifndef _V4L2_CCI_H
> +#define _V4L2_CCI_H
> +
> +#include <linux/regmap.h>
> +#include <linux/types.h>
> +
> +/*
> + * Note cci_reg_8 deliberately is 0, not 1, so that raw
> + * (not wrapped in a CCI_REG*() macro) register addresses
> + * do 8 bit wide accesses. This allows unchanged use of register
> + * initialization lists of raw address, value pairs which only
> + * do 8 bit width accesses. Which makes porting drivers easier.
> + */
> +enum cci_reg_type {
> +	cci_reg_8 = 0,
> +	cci_reg_16,
> +	cci_reg_24,
> +	cci_reg_32,
> +};
> +
> +/*
> + * Macros to define register address with the register width encoded
> + * into the higher bits. CCI_REG8() is a no-op so its use is optional.
> + */
> +#define CCI_REG_ADDR_MASK		GENMASK(15, 0)
> +#define CCI_REG_WIDTH_SHIFT		16
> +#define CCI_REG_WIDTH_MASK		GENMASK(17, 16)
> +
> +#define CCI_REG8(x)			((cci_reg_8 << CCI_REG_WIDTH_SHIFT) | (x))
> +#define CCI_REG16(x)			((cci_reg_16 << CCI_REG_WIDTH_SHIFT) | (x))
> +#define CCI_REG24(x)			((cci_reg_24 << CCI_REG_WIDTH_SHIFT) | (x))
> +#define CCI_REG32(x)			((cci_reg_32 << CCI_REG_WIDTH_SHIFT) | (x))

I'd drop enum ccsi_reg_type and just define the values here using plain
numbers. How you test which width you have changes a little but not
necessarily for worse. Up to you.

> +
> +/**
> + * cci_read() - Read a value from a single CCI register
> + *
> + * @map: Register map to write to
> + * @reg: Register address to write, use CCI_REG#() macros to encode reg width
> + * @val: Pointer to store read value
> + * @err: optional pointer to store errors, if a previous error is set the write will be skipped
> + *
> + * Return: %0 on success or a negative error code on failure.
> + */
> +int cci_read(struct regmap *map, u32 reg, u32 *val, int *err);
> +
> +/**
> + * cci_write() - Write a value to a single CCI register
> + *
> + * @map: Register map to write to
> + * @reg: Register address to write, use CCI_REG#() macros to encode reg width
> + * @val: Value to be written
> + * @err: optional pointer to store errors, if a previous error is set the write will be skipped
> + *
> + * Return: %0 on success or a negative error code on failure.
> + */
> +int cci_write(struct regmap *map, u32 reg, u32 val, int *err);
> +
> +/**
> + * cci_update_bits() - Perform a read/modify/write cycle on a single CCI register
> + *
> + * @map: Register map to write to
> + * @reg: Register address to write, use CCI_REG#() macros to encode reg width
> + * @mask: Bitmask to change
> + * @val: New value for bitmask
> + * @err: optional pointer to store errors, if a previous error is set the update will be skipped
> + *
> + * For 8 bit width registers this is guaranteed to be atomic wrt other
> + * cci_*() register access functions. For multi-byte width registers
> + * atomicity is NOT guaranteed.
> + *
> + * Return: %0 on success or a negative error code on failure.
> + */
> +int cci_update_bits(struct regmap *map, u32 reg, u32 mask, u32 val, int *err);
> +
> +/**
> + * cci_multi_reg_write() - Write multiple registers to the device
> + *
> + * @map: Register map to write to
> + * @regs: Array of structures containing register-address, value pairs to be written
> + *        register-addresses use CCI_REG#() macros to encode reg width
> + * @num_regs: Number of registers to write
> + * @err: optional pointer to store errors, if a previous error is set the update will be skipped
> + *
> + * Write multiple registers to the device where the set of register, value
> + * pairs are supplied in any order, possibly not all in a single range.
> + *
> + * Return: %0 on success or a negative error code on failure.
> + */
> +int cci_multi_reg_write(struct regmap *map, const struct reg_sequence *regs, int num_regs, int *err);
> +
> +/**
> + * cci_regmap_init_i2c() - Create regmap to use with cci_*() register access functions
> + *
> + * @client: i2c_client to create the regmap for
> + * @reg_addr_bits: register address width to use (8 or 16)
> + *
> + * Note the memory for the created regmap is devm() managed, tied to the client.
> + *
> + * Return: %0 on success or a negative error code on failure.
> + */
> +struct regmap *cci_regmap_init_i2c(struct i2c_client *client, int reg_addr_bits);
> +
> +#endif

-- 
Kind regards,

Sakari Ailus