Re: [PATCH v9 10/15] media: uapi: Add V4L2_CTRL_TYPE_FIXED_POINT

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;