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

From: Hans Verkuil
Date: Fri Nov 17 2023 - 09:05:26 EST

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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@xxxxxxxxx>
>> ---
>> 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;
>

Next message: Andrew Lunn: "Re: [PATCH] firmware_loader: Expand Firmware upload error codes with firmware invalid error"
Previous message: Andrew Davis: "Re: [PATCH] docs: dt-bindings: add DTS Coding Style document"
In reply to: Sakari Ailus: "Re: [PATCH v9 10/15] media: uapi: Add V4L2_CTRL_TYPE_FIXED_POINT"
Next in thread: Shengjiu Wang: "Re: [PATCH v9 10/15] media: uapi: Add V4L2_CTRL_TYPE_FIXED_POINT"
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