Re: [PATCH v1 02/11] media: uapi: v4l2-isp: Add v4l2 ISP extensible statistics definitions

[Jacopo Mondi]

Hi Antoine

On Thu, Apr 16, 2026 at 12:03:24PM +0200, Jacopo Mondi wrote:
> Hello Antoine,
>    thanks for the update
>
> On Mon, Apr 13, 2026 at 06:03:22PM +0200, Antoine Bouyer wrote:
> > Extend the v4l2-isp extensible format introduced for isp parameters buffer
> > to the statistics buffer as well.
> >
> > Like for ISP configuration purpose, that will help supporting various ISP
> > hardware versions reporting different statistics data with less impact on
> > userspace.
> >
> > The `v4l2_isp_stats_buffer` reuses the `v4l2_isp_params_buffer` container
> > definitions, with similar header, versions and flags. V0 and V1 versions
> > are provided to match with params versions. On the other side, ENABLE and
> > DISABLE flags are not really meaningfull for statistics purpose. So VALID
> > and INVALID flags are introduced. Purpose is to force ISP driver to
> > validate a statistics buffer, before it is consumed by userspace.
>
> Is this a leftover ?
>
> I don't see VALID and INVALID in this patch and unless I've missed it
> badly I don't see them in the next patches.
>
> I'm fine without them, I'm not sure how you intend to use them to
> force drivers to validate a statistics buffer.
>
> >
> > Signed-off-by: Antoine Bouyer <antoine.bouyer@xxxxxxx>
> > ---
> >  include/uapi/linux/media/v4l2-isp.h | 148 +++++++++++++++++++---------
> >  1 file changed, 100 insertions(+), 48 deletions(-)
> >
> > diff --git a/include/uapi/linux/media/v4l2-isp.h b/include/uapi/linux/media/v4l2-isp.h
> > index 779168f9058e..e84476280d43 100644
> > --- a/include/uapi/linux/media/v4l2-isp.h
> > +++ b/include/uapi/linux/media/v4l2-isp.h
> > @@ -13,25 +13,33 @@
> >  #include <linux/types.h>
> >
> >  /**
> > - * enum v4l2_isp_params_version - V4L2 ISP parameters versioning
> > + * enum v4l2_isp_version - V4L2 ISP serialization format versioning
> >   *
> > - * @V4L2_ISP_PARAMS_VERSION_V0: First version of the V4L2 ISP parameters format
> > - *				(for compatibility)
> > - * @V4L2_ISP_PARAMS_VERSION_V1: First version of the V4L2 ISP parameters format
> > + * @V4L2_ISP_VERSION_V0: First version of the V4L2 ISP serialization format
> > + *                       (for compatibility)
> > + * @V4L2_ISP_VERSION_V1: First version of the V4L2 ISP serialization format
> >   *
> >   * V0 and V1 are identical in order to support drivers compatible with the V4L2
> > - * ISP parameters format already upstreamed which use either 0 or 1 as their
> > - * versioning identifier. Both V0 and V1 refers to the first version of the
> > - * V4L2 ISP parameters format.
> > + * ISP format already upstreamed which use either 0 or 1 as their versioning
> > + * identifier. Both V0 and V1 refers to the first version of the V4L2 ISP
> > + * serialization format.
> >   *
> > - * Future revisions of the V4L2 ISP parameters format should start from the
> > + * Future revisions of the V4L2 ISP serialization format should start from the
> >   * value of 2.
> >   */
> > -enum v4l2_isp_params_version {
> > -	V4L2_ISP_PARAMS_VERSION_V0 = 0,
> > -	V4L2_ISP_PARAMS_VERSION_V1
> > +enum v4l2_isp_version {
> > +	V4L2_ISP_VERSION_V0 = 0,
> > +	V4L2_ISP_VERSION_V1
> >  };
> >
> > +/*
> > + * Compatibility with existing users of v4l2_isp_params which pre-date the
> > + * introduction of v4l2_isp_stats.
> > + */
> > +#define v4l2_isp_params_version			v4l2_isp_version
> > +#define V4L2_ISP_PARAMS_VERSION_V0		V4L2_ISP_VERSION_V0
> > +#define V4L2_ISP_PARAMS_VERSION_V1		V4L2_ISP_VERSION_V1
> > +
> >  #define V4L2_ISP_PARAMS_FL_BLOCK_DISABLE	(1U << 0)
> >  #define V4L2_ISP_PARAMS_FL_BLOCK_ENABLE		(1U << 1)
> >
> > @@ -39,64 +47,108 @@ enum v4l2_isp_params_version {
> >   * Reserve the first 8 bits for V4L2_ISP_PARAMS_FL_* flag.
> >   *
> >   * Driver-specific flags should be defined as:
> > - * #define DRIVER_SPECIFIC_FLAG0     ((1U << V4L2_ISP_PARAMS_FL_DRIVER_FLAGS(0))
> > - * #define DRIVER_SPECIFIC_FLAG1     ((1U << V4L2_ISP_PARAMS_FL_DRIVER_FLAGS(1))
> > + * #define DRIVER_SPECIFIC_FLAG0     ((1U << V4L2_ISP_FL_DRIVER_FLAGS(0))
> > + * #define DRIVER_SPECIFIC_FLAG1     ((1U << V4L2_ISP_FL_DRIVER_FLAGS(1))
> >   */
> > -#define V4L2_ISP_PARAMS_FL_DRIVER_FLAGS(n)       ((n) + 8)
> > +#define V4L2_ISP_FL_DRIVER_FLAGS(n)		((n) + 8)
> >
> >  /**
> > - * struct v4l2_isp_params_block_header - V4L2 extensible parameters block header
> > - * @type: The parameters block type (driver-specific)
> > + * struct v4l2_isp_block_header - V4L2 extensible block header
> > + * @type: The parameters or statistics block type (driver-specific)
> >   * @flags: A bitmask of block flags (driver-specific)
> > - * @size: Size (in bytes) of the parameters block, including this header
> > + * @size: Size (in bytes) of the block, including this header
> >   *
> > - * This structure represents the common part of all the ISP configuration
> > - * blocks. Each parameters block shall embed an instance of this structure type
> > - * as its first member, followed by the block-specific configuration data.
> > + * This structure represents the common part of all the ISP configuration or
> > + * statistic blocks. Each block shall embed an instance of this structure type
> > + * as its first member, followed by the block-specific configuration or
> > + * statistic data.
> >   *
> >   * The @type field is an ISP driver-specific value that identifies the block
> > - * type. The @size field specifies the size of the parameters block.
> > - *
> > - * The @flags field is a bitmask of per-block flags V4L2_PARAMS_ISP_FL_* and
> > - * driver-specific flags specified by the driver header.
> > + * type. The @size field specifies the size of the block, including this
> > + * header.
> >   */
> > -struct v4l2_isp_params_block_header {
> > +struct v4l2_isp_block_header {
> >  	__u16 type;
> >  	__u16 flags;
> >  	__u32 size;
> >  } __attribute__((aligned(8)));
> >
> >  /**
> > - * struct v4l2_isp_params_buffer - V4L2 extensible parameters configuration
> > - * @version: The parameters buffer version (driver-specific)
> > - * @data_size: The configuration data effective size, excluding this header
> > - * @data: The configuration data
> > + * v4l2_isp_params_block_header - V4L2 extensible parameters block header
> >   *
> > - * This structure contains the configuration parameters of the ISP algorithms,
> > - * serialized by userspace into a data buffer. Each configuration parameter
> > - * block is represented by a block-specific structure which contains a
> > - * :c:type:`v4l2_isp_params_block_header` entry as first member. Userspace
> > - * populates the @data buffer with configuration parameters for the blocks that
> > - * it intends to configure. As a consequence, the data buffer effective size
> > - * changes according to the number of ISP blocks that userspace intends to
> > - * configure and is set by userspace in the @data_size field.
> > - *
> > - * The parameters buffer is versioned by the @version field to allow modifying
> > - * and extending its definition. Userspace shall populate the @version field to
> > - * inform the driver about the version it intends to use. The driver will parse
> > - * and handle the @data buffer according to the data layout specific to the
> > - * indicated version and return an error if the desired version is not
> > + * This structure represents the common part of all the ISP configuration blocks
> > + * and is identical to :c:type:`v4l2_isp_block_header`.
> > + *
> > + * The @flags field is a bitmask of per-block flags V4L2_ISP_PARAMS_FL_* and
> > + * driver-specific flags specified by the driver header.
>
> What if we move this to the documentation of struct v4l2_isp_block_header
> and we only document the macro for compatibility reasons like you did
> for `v4l2_isp_params_version` ?
>
> We could add the above to the documentation of `struct
> v4l2_isp_block_header`:
>
>  * The @flags field is a bitmask of per-block flags. If a block is used for
>  * configuration parameters this field can be a combination of
>  * V4L2_ISP_PARAMS_FL_ and driver-specific flags.
>
> Depending on the answer on VALID/INVALID we can document the usage of
> flags for stats as:
>
>  * The @flags field is a bitmask of per-block flags. If a block is used for
>  * configuration parameters this field can be a combination of
>  * V4L2_ISP_PARAMS_FL_ and driver-specific flags. If a block is used

Just one note, please use V4L2_ISP_PARAMS_FL_* as otherwise building
documentation will raise warnings.

>  * for statistics this fields is used to report optional
>  * driver-specific flags, if any.
>
>
> > + */
> > +#define v4l2_isp_params_block_header v4l2_isp_block_header
>
> If you accept the above suggestion we can simply document this
>
> /**
>  * v4l2_isp_params_block_header - V4L2 extensible parameters compatibility
>  *
>  * Compatibility with existing users of v4l2_isp_params_block_header
>  * which pre-date the introduction of v4l2_isp_block_header.
>  *.
>
> > +
> > +/**
> > + * v4l2_isp_stats_block_header - V4L2 extensible statistics block header
> > + *
> > + * This structure represents the common part of all the ISP statistics blocks
> > + * and is identical to :c:type:`v4l2_isp_block_header`.
> > + *
> > + * The @flags field is a bitmask of driver-specific flags specified by the
> > + * driver header, as there is no generic flags for statistics.
> > + */
> > +#define v4l2_isp_stats_block_header v4l2_isp_block_header
>
> Do we need this or should we use v4l2_isp_block_header unconditionally ?
>
> > +
> > +/**
> > + * struct v4l2_isp_buffer - V4L2 extensible buffer
> > + * @version: The extensible buffer version (driver-specific)
> > + * @data_size: The data effective size, excluding this header
> > + * @data: The configuration or statistics data
> > + *
> > + * This structure contains ISP configuration parameters or ISP hardware
> > + * statistics serialized into a data buffer. Each block is represented by a
> > + * block-specific structure which contains a :c:type:`v4l2_isp_block_header`
> > + * entry as first member.
> > + *
> > + * For a parameters block, userspace populates the @data buffer with
>
> Or:
>
>     * When used for ISP parameters userspace ..
>
> > + * configuration parameters for the blocks that it intends to configure.
> > + * As a consequence, the data buffer effective size changes according to the
> > + * number of ISP blocks that userspace intends to configure and is set by
> > + * userspace in the @data_size field.
> > + *
> > + * For a statistics block, behavior is the same as for parameters, except that
>
> Or:
>
>     * When used to report ISP statistics the driver populates the
>     * @data buffer with statistics for each supported measurement
>     * block. The buffer effective size is set by the driver in the
>     * @data_size field.
>
> > + * buffer is filled by the ISP driver.
> > + *
> > + * The buffer is versioned by the @version field to allow modifying
> > + * and extending its definition. The writer shall populate the @version field
> > + * to inform the reader about the version it intends to use. The reader will
> > + * parse and handle the @data buffer according to the data layout specific to
> > + * the indicated version and return an error if the desired version is not
> >   * supported.
>
> Ack, I think using "writer" and "reader" is clear enough to support
> both the params and stats use case. If we want more clarity we can add
> to "driver" and "userspace" a "(role)" in the two previous paragraph.
> Something like:
>
>     * When used for ISP parameters userspace (the writer) populates
>     * the @data buffer ...
>
> >   *
> > - * For each ISP block that userspace wants to configure, a block-specific
> > - * structure is appended to the @data buffer, one after the other without gaps
> > - * in between. Userspace shall populate the @data_size field with the effective
> > - * size, in bytes, of the @data buffer.
> > + * For each ISP block, a block-specific structure is appended to the @data
> > + * buffer, one after the other without gaps in between. The writer shall
> > + * populate the @data_size field with the effective size, in bytes, of the
> > + * @data buffer.
>
> If we want to describe @data_size here we can remove it from the above
> two paragraphs maybe. I think it's fine to have it here only.
>
> >   */
> > -struct v4l2_isp_params_buffer {
> > +struct v4l2_isp_buffer {
> >  	__u32 version;
> >  	__u32 data_size;
> >  	__u8 data[] __counted_by(data_size);
> >  };
> >
> > +/**
> > + * v4l2_isp_params_buffer - V4L2 extensible parameters configuration
>
> s/configuration/compatibility
>
> > + *
> > + * This structure contains the configuration parameters of the ISP algorithms,
> > + * serialized into a data buffer. It is identical to
> > + * :c:type:`v4l2_isp_buffer`.
>
> And here only
>
>  * Compatibility with existing users of v4l2_isp_params_buffer which
>  * pre-date the introduction of v4l2_isp_buffer
>
> > + */
> > +#define v4l2_isp_params_buffer v4l2_isp_buffer
> > +
> > +/**
> > + * v4l2_isp_stats_buffer - V4L2 extensible statistics buffer
> > + *
> > + * This structure contains the statistics data from the ISP hardware,
> > + * serialized into a data buffer. It is identical to
> > + * :c:type:`v4l2_isp_buffer`.
> > + */
> > +#define v4l2_isp_stats_buffer v4l2_isp_buffer
>
> Same question as per `v4l2_isp_stats_block_header`. Do we need it ?
>
> Thanks
>   j
>
> > +
> >  #endif /* _UAPI_V4L2_ISP_H_ */
> > --
> > 2.51.0
> >