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Message-ID: <4e0e0e79-91a8-49b5-874d-784d51003021@xs4all.nl>
Date:   Fri, 17 Nov 2023 15:05:14 +0100
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v9 10/15] media: uapi: Add V4L2_CTRL_TYPE_FIXED_POINT
Content-Language: en-US, nl
To:     Sakari Ailus <sakari.ailus@iki.fi>
Cc:     Shengjiu Wang <shengjiu.wang@gmail.com>,
        Shengjiu Wang <shengjiu.wang@nxp.com>,
        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>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>
References: <da6efe14-c00d-4bf4-bf61-dd4ed39c5c60@xs4all.nl>
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 <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>
 <ZVdlmRlpW7ebrjQO@valkosipuli.retiisi.eu>
From:   Hans Verkuil <hverkuil@xs4all.nl>
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In-Reply-To: <ZVdlmRlpW7ebrjQO@valkosipuli.retiisi.eu>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 17/11/2023 14:07, Sakari Ailus wrote:
> 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 wonder if we could add a printk() format specifier for this. Doesn't need
> to be done right now though, just an idea.
> 
>>
>> 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.
>>
>> 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;
> 
> u8 would suffice. Not that we'd be short of space but still...
> 
>> +	__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);
> 
> Why not just:
> 
> 	return v >> fraction_bits;

That works if v >= 0, but not for v < 0. Getting this right for negative
fixed point values was rather tricky. Actually, it is still wrong if
fraction_bits == 63. This works:

static inline long long v4l2_fp_integer(long long v, unsigned int fraction_bits)
{
        if (fraction_bits >= 63)
                return v < 0 ? -1 : 0;
        return v / (1ULL << fraction_bits);
}

> 
> I'd use macros so you could use whatever control types with this without
> casting. E.g.
> 
> #define V4L2_FP_INTEGER(v, fraction_bits) ((v) >> fraction_bits)
> 
> A more generic way to expose this could be to have base and exponent, the
> base being 2 in this case. Just an idea. This would of course be a little
> bit more difficult to use.

To be honest, I am not at all certain this should be in a public header.
I am inclined to drop it, especially since in userspace you can just use
floating point operations which makes working with fixed point a lot easier.

The code to extract the integer and fraction part is really only relevant
when logging the fixed point value.

Regards,

	Hans

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