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Date:   Fri, 17 Nov 2023 14:55:30 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Hans Verkuil <hverkuil@xs4all.nl>
Cc:     Shengjiu Wang <shengjiu.wang@gmail.com>,
        Shengjiu Wang <shengjiu.wang@nxp.com>,
        Sakari Ailus <sakari.ailus@iki.fi>, m.szyprowski@samsung.com,
        mchehab@kernel.org, linux-media@vger.kernel.org,
        linux-kernel@vger.kernel.org, Xiubo.Lee@gmail.com,
        festevam@gmail.com, nicoleotsuka@gmail.com, lgirdwood@gmail.com,
        broonie@kernel.org, perex@perex.cz, tiwai@suse.com,
        alsa-devel@alsa-project.org, linuxppc-dev@lists.ozlabs.org,
        Tomasz Figa <tfiga@chromium.org>
Subject: Re: [PATCH v9 10/15] media: uapi: Add V4L2_CTRL_TYPE_FIXED_POINT
Message-ID: <20231117125530.GK21041@pendragon.ideasonboard.com>
References: <da6efe14-c00d-4bf4-bf61-dd4ed39c5c60@xs4all.nl>
 <20231113124412.GA18974@pendragon.ideasonboard.com>
 <b35601f7-8bb2-4317-a8f7-6fbf81572943@xs4all.nl>
 <20231115105518.GD13826@pendragon.ideasonboard.com>
 <a67491c0-4fdf-4472-852c-e75f5e1d67af@xs4all.nl>
 <20231115114931.GE13826@pendragon.ideasonboard.com>
 <CAAFQd5BkCR=tYvmfjkOeTnjnccmURt8kEtiRee9CYqcz+FGHfg@mail.gmail.com>
 <7626e0f8-ce31-469e-b49c-f2fba664756f@xs4all.nl>
 <CAA+D8ANb6A9eh=MQR9+7sZi5jet+7RSHt6TdZqPz5EK6pBs3mA@mail.gmail.com>
 <6badc94c-c414-40d7-a9d7-8b3fc86d8d98@xs4all.nl>
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In-Reply-To: <6badc94c-c414-40d7-a9d7-8b3fc86d8d98@xs4all.nl>
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Hi Hans,

Thank you for the patch.

On Fri, Nov 17, 2023 at 01:07:44PM +0100, Hans Verkuil wrote:
> Here is an RFC patch adding support for 'fraction_bits'. It's lacking
> documentation, but it can be used for testing.
> 
> It was rather a pain logging fixed point number in a reasonable format,
> but I think it is OK.
> 
> In userspace (where you can use floating point) it is a lot easier:
> 
> printf("%.*g\n", fraction_bits, (double)v * (1.0 / (1ULL << fraction_bits)));
> 
> I decided to only expose fraction_bits in struct v4l2_query_ext_ctrl.
> I could add it to struct v4l2_queryctrl, but I did not think that was
> necessary. Other opinions are welcome.

Agreed.

> In the meantime, let me know if this works for your patch series. If it
> does, then I can clean this up.
> 
> Regards,
> 
> 	Hans
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> ---
>  drivers/media/v4l2-core/v4l2-ctrls-api.c  |  1 +
>  drivers/media/v4l2-core/v4l2-ctrls-core.c | 72 +++++++++++++++++++----
>  include/media/v4l2-ctrls.h                |  7 ++-
>  include/uapi/linux/videodev2.h            | 20 ++++++-
>  4 files changed, 85 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-api.c b/drivers/media/v4l2-core/v4l2-ctrls-api.c
> index 002ea6588edf..3132df315b17 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-api.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-api.c
> @@ -1101,6 +1101,7 @@ int v4l2_query_ext_ctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_query_ext_ctr
>  	qc->elems = ctrl->elems;
>  	qc->nr_of_dims = ctrl->nr_of_dims;
>  	memcpy(qc->dims, ctrl->dims, qc->nr_of_dims * sizeof(qc->dims[0]));
> +	qc->fraction_bits = ctrl->fraction_bits;
>  	qc->minimum = ctrl->minimum;
>  	qc->maximum = ctrl->maximum;
>  	qc->default_value = ctrl->default_value;
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-core.c b/drivers/media/v4l2-core/v4l2-ctrls-core.c
> index a662fb60f73f..0e08a371af5c 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-core.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-core.c
> @@ -252,12 +252,42 @@ void v4l2_ctrl_type_op_init(const struct v4l2_ctrl *ctrl, u32 from_idx,
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_type_op_init);
> 
> +static void v4l2_ctrl_log_fp(s64 v, unsigned int fraction_bits)
> +{
> +	s64 i = v4l2_fp_integer(v, fraction_bits);
> +	s64 f = v4l2_fp_fraction(v, fraction_bits);
> +
> +	if (!f) {
> +		pr_cont("%lld", i);
> +	} else if (fraction_bits < 20) {
> +		u64 div = 1ULL << fraction_bits;
> +
> +		if (!i && f < 0)
> +			pr_cont("-%lld/%llu", -f, div);
> +		else if (!i)
> +			pr_cont("%lld/%llu", f, div);
> +		else if (i < 0 || f < 0)
> +			pr_cont("-%lld-%llu/%llu", -i, -f, div);
> +		else
> +			pr_cont("%lld+%llu/%llu", i, f, div);
> +	} else {
> +		if (!i && f < 0)
> +			pr_cont("-%lld/(2^%u)", -f, fraction_bits);
> +		else if (!i)
> +			pr_cont("%lld/(2^%u)", f, fraction_bits);
> +		else if (i < 0 || f < 0)
> +			pr_cont("-%lld-%llu/(2^%u)", -i, -f, fraction_bits);
> +		else
> +			pr_cont("%lld+%llu/(2^%u)", i, f, fraction_bits);
> +	}
> +}
> +
>  void v4l2_ctrl_type_op_log(const struct v4l2_ctrl *ctrl)
>  {
>  	union v4l2_ctrl_ptr ptr = ctrl->p_cur;
> 
>  	if (ctrl->is_array) {
> -		unsigned i;
> +		unsigned int i;
> 
>  		for (i = 0; i < ctrl->nr_of_dims; i++)
>  			pr_cont("[%u]", ctrl->dims[i]);
> @@ -266,7 +296,10 @@ void v4l2_ctrl_type_op_log(const struct v4l2_ctrl *ctrl)
> 
>  	switch (ctrl->type) {
>  	case V4L2_CTRL_TYPE_INTEGER:
> -		pr_cont("%d", *ptr.p_s32);
> +		if (!ctrl->fraction_bits)
> +			pr_cont("%d", *ptr.p_s32);
> +		else
> +			v4l2_ctrl_log_fp(*ptr.p_s32, ctrl->fraction_bits);
>  		break;
>  	case V4L2_CTRL_TYPE_BOOLEAN:
>  		pr_cont("%s", *ptr.p_s32 ? "true" : "false");
> @@ -281,19 +314,31 @@ void v4l2_ctrl_type_op_log(const struct v4l2_ctrl *ctrl)
>  		pr_cont("0x%08x", *ptr.p_s32);
>  		break;
>  	case V4L2_CTRL_TYPE_INTEGER64:
> -		pr_cont("%lld", *ptr.p_s64);
> +		if (!ctrl->fraction_bits)
> +			pr_cont("%lld", *ptr.p_s64);
> +		else
> +			v4l2_ctrl_log_fp(*ptr.p_s64, ctrl->fraction_bits);
>  		break;
>  	case V4L2_CTRL_TYPE_STRING:
>  		pr_cont("%s", ptr.p_char);
>  		break;
>  	case V4L2_CTRL_TYPE_U8:
> -		pr_cont("%u", (unsigned)*ptr.p_u8);
> +		if (!ctrl->fraction_bits)
> +			pr_cont("%u", (unsigned int)*ptr.p_u8);
> +		else
> +			v4l2_ctrl_log_fp((unsigned int)*ptr.p_u8, ctrl->fraction_bits);
>  		break;
>  	case V4L2_CTRL_TYPE_U16:
> -		pr_cont("%u", (unsigned)*ptr.p_u16);
> +		if (!ctrl->fraction_bits)
> +			pr_cont("%u", (unsigned int)*ptr.p_u16);
> +		else
> +			v4l2_ctrl_log_fp((unsigned int)*ptr.p_u16, ctrl->fraction_bits);
>  		break;
>  	case V4L2_CTRL_TYPE_U32:
> -		pr_cont("%u", (unsigned)*ptr.p_u32);
> +		if (!ctrl->fraction_bits)
> +			pr_cont("%u", (unsigned int)*ptr.p_u32);
> +		else
> +			v4l2_ctrl_log_fp((unsigned int)*ptr.p_u32, ctrl->fraction_bits);
>  		break;
>  	case V4L2_CTRL_TYPE_H264_SPS:
>  		pr_cont("H264_SPS");
> @@ -1752,7 +1797,7 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>  			u32 id, const char *name, enum v4l2_ctrl_type type,
>  			s64 min, s64 max, u64 step, s64 def,
>  			const u32 dims[V4L2_CTRL_MAX_DIMS], u32 elem_size,
> -			u32 flags, const char * const *qmenu,
> +			u32 fraction_bits, u32 flags, const char * const *qmenu,
>  			const s64 *qmenu_int, const union v4l2_ctrl_ptr p_def,
>  			void *priv)
>  {
> @@ -1939,6 +1984,7 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>  	ctrl->name = name;
>  	ctrl->type = type;
>  	ctrl->flags = flags;
> +	ctrl->fraction_bits = fraction_bits;
>  	ctrl->minimum = min;
>  	ctrl->maximum = max;
>  	ctrl->step = step;
> @@ -2037,7 +2083,7 @@ struct v4l2_ctrl *v4l2_ctrl_new_custom(struct v4l2_ctrl_handler *hdl,
>  	ctrl = v4l2_ctrl_new(hdl, cfg->ops, cfg->type_ops, cfg->id, name,
>  			type, min, max,
>  			is_menu ? cfg->menu_skip_mask : step, def,
> -			cfg->dims, cfg->elem_size,
> +			cfg->dims, cfg->elem_size, cfg->fraction_bits,
>  			flags, qmenu, qmenu_int, cfg->p_def, priv);
>  	if (ctrl)
>  		ctrl->is_private = cfg->is_private;
> @@ -2062,7 +2108,7 @@ struct v4l2_ctrl *v4l2_ctrl_new_std(struct v4l2_ctrl_handler *hdl,
>  		return NULL;
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
> -			     min, max, step, def, NULL, 0,
> +			     min, max, step, def, NULL, 0, 0,
>  			     flags, NULL, NULL, ptr_null, NULL);
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_std);
> @@ -2095,7 +2141,7 @@ struct v4l2_ctrl *v4l2_ctrl_new_std_menu(struct v4l2_ctrl_handler *hdl,
>  		return NULL;
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
> -			     0, max, mask, def, NULL, 0,
> +			     0, max, mask, def, NULL, 0, 0,
>  			     flags, qmenu, qmenu_int, ptr_null, NULL);
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_std_menu);
> @@ -2127,7 +2173,7 @@ struct v4l2_ctrl *v4l2_ctrl_new_std_menu_items(struct v4l2_ctrl_handler *hdl,
>  		return NULL;
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
> -			     0, max, mask, def, NULL, 0,
> +			     0, max, mask, def, NULL, 0, 0,
>  			     flags, qmenu, NULL, ptr_null, NULL);
> 
>  }
> @@ -2149,7 +2195,7 @@ struct v4l2_ctrl *v4l2_ctrl_new_std_compound(struct v4l2_ctrl_handler *hdl,
>  		return NULL;
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
> -			     min, max, step, def, NULL, 0,
> +			     min, max, step, def, NULL, 0, 0,
>  			     flags, NULL, NULL, p_def, NULL);
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_std_compound);
> @@ -2173,7 +2219,7 @@ struct v4l2_ctrl *v4l2_ctrl_new_int_menu(struct v4l2_ctrl_handler *hdl,
>  		return NULL;
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
> -			     0, max, 0, def, NULL, 0,
> +			     0, max, 0, def, NULL, 0, 0,
>  			     flags, NULL, qmenu_int, ptr_null, NULL);
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_int_menu);
> diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
> index 59679a42b3e7..c35514c5bf88 100644
> --- a/include/media/v4l2-ctrls.h
> +++ b/include/media/v4l2-ctrls.h
> @@ -211,7 +211,8 @@ typedef void (*v4l2_ctrl_notify_fnc)(struct v4l2_ctrl *ctrl, void *priv);
>   *		except for dynamic arrays. In that case it is in the range of
>   *		1 to @p_array_alloc_elems.
>   * @dims:	The size of each dimension.
> - * @nr_of_dims:The number of dimensions in @dims.
> + * @nr_of_dims: The number of dimensions in @dims.
> + * @fraction_bits: The number of fraction bits for fixed point values.
>   * @menu_skip_mask: The control's skip mask for menu controls. This makes it
>   *		easy to skip menu items that are not valid. If bit X is set,
>   *		then menu item X is skipped. Of course, this only works for
> @@ -228,6 +229,7 @@ typedef void (*v4l2_ctrl_notify_fnc)(struct v4l2_ctrl *ctrl, void *priv);
>   *		:math:`ceil(\frac{maximum - minimum}{step}) + 1`.
>   *		Used only if the @type is %V4L2_CTRL_TYPE_INTEGER_MENU.
>   * @flags:	The control's flags.
> + * @fraction_bits: The number of fraction bits for fixed point values.
>   * @priv:	The control's private pointer. For use by the driver. It is
>   *		untouched by the control framework. Note that this pointer is
>   *		not freed when the control is deleted. Should this be needed
> @@ -286,6 +288,7 @@ struct v4l2_ctrl {
>  	u32 new_elems;
>  	u32 dims[V4L2_CTRL_MAX_DIMS];
>  	u32 nr_of_dims;
> +	u32 fraction_bits;
>  	union {
>  		u64 step;
>  		u64 menu_skip_mask;
> @@ -426,6 +429,7 @@ struct v4l2_ctrl_handler {
>   * @dims:	The size of each dimension.
>   * @elem_size:	The size in bytes of the control.
>   * @flags:	The control's flags.
> + * @fraction_bits: The number of fraction bits for fixed point values.
>   * @menu_skip_mask: The control's skip mask for menu controls. This makes it
>   *		easy to skip menu items that are not valid. If bit X is set,
>   *		then menu item X is skipped. Of course, this only works for
> @@ -455,6 +459,7 @@ struct v4l2_ctrl_config {
>  	u32 dims[V4L2_CTRL_MAX_DIMS];
>  	u32 elem_size;
>  	u32 flags;
> +	u32 fraction_bits;
>  	u64 menu_skip_mask;
>  	const char * const *qmenu;
>  	const s64 *qmenu_int;
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index c3d4e490ce7c..26ecac19722a 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1944,9 +1944,27 @@ struct v4l2_query_ext_ctrl {
>  	__u32                elems;
>  	__u32                nr_of_dims;
>  	__u32                dims[V4L2_CTRL_MAX_DIMS];
> -	__u32		     reserved[32];
> +	__u32                fraction_bits;

Thinking forward, what if the control uses a different type of
quantization, for instance if the control is exponential instead of
linear ? Is this something we want to plan for already (without
necessarily implementing it yet) ? For instance, the CCS spec defines a
linear gain model where the gain is expressed as

	gain = (m0 * x + c0) / (m1 * x + c1)

where x is the control value, gain is the real gain, and m0, c0, m1 and
c1 are device-specific 16-bit integer constants (with the constraint
that one of m0 and m1 has to be zero, but not both).

There's also an exponential model in CCS, with

	gain = linear_gain * 2 ^ exponential_gain

where linear_gain and exponential_gain are U8.8 values.

> +	__u32		     reserved[31];
>  };
> 
> +static inline __s64 v4l2_fp_compose(__s64 i, __s64 f, unsigned int fraction_bits)
> +{
> +	return (i << fraction_bits) + f;
> +}
> +
> +static inline __s64 v4l2_fp_integer(__s64 v, unsigned int fraction_bits)
> +{
> +	return v / (1LL << fraction_bits);
> +}
> +
> +static inline __s64 v4l2_fp_fraction(__s64 v, unsigned int fraction_bits)
> +{
> +	__u64 mask = (1ULL << fraction_bits) - 1;
> +
> +	return v < 0 ? -((-v) & mask) : (v & mask);
> +}

I woudln't add static inline functions to the UAPI. They cause licensing
issues, and increase the UAPI surface, thus making UAPI evolutions more
difficult.

> +
>  /*  Used in the VIDIOC_QUERYMENU ioctl for querying menu items */
>  struct v4l2_querymenu {
>  	__u32		id;

-- 
Regards,

Laurent Pinchart