Re: [PATCH v4] [media] vivi: Teach it to tune FPS

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 17-11-2012 08:45, Kirill Smelkov escreveu:
> On Fri, Nov 16, 2012 at 01:46:58PM -0200, Mauro Carvalho Chehab wrote:
>> Em 16-11-2012 11:38, Hans Verkuil escreveu:
>>> On Wed November 7 2012 12:30:01 Kirill Smelkov wrote:
> [...]
>
>>>> diff --git a/drivers/media/platform/vivi.c b/drivers/media/platform/vivi.c
>>>> index 37d0af8..5d1b374 100644
>>>> --- a/drivers/media/platform/vivi.c
>>>> +++ b/drivers/media/platform/vivi.c
>>>> @@ -65,8 +65,11 @@ MODULE_PARM_DESC(vid_limit, "capture memory limit in megabytes");
>>>>   /* Global font descriptor */
>>>>   static const u8 *font8x16;
>>>>
>>>> -/* default to NTSC timeperframe */
>>>> -static const struct v4l2_fract TPF_DEFAULT = {.numerator = 1001, .denominator = 30000};
>>>> +/* timeperframe: min/max and default */
>>>> +static const struct v4l2_fract
>>>> +	tpf_min     = {.numerator = 1,		.denominator = UINT_MAX},  /* 1/infty */
>>>> +	tpf_max     = {.numerator = UINT_MAX,	.denominator = 1},         /* infty */
>>>
>>> I understand your reasoning here, but I wouldn't go with UINT_MAX here. Something like
>>> 1/1000 tpf (or 1 ms) up to 86400/1 tpf (or once a day). With UINT_MAX I am afraid we
>>> might hit application errors when they manipulate these values. The shortest time
>>> between frames is 1 ms anyway.
>>>
>>> It's the only comment I have, it looks good otherwise.
>>
>> As those will be a arbitrary values, I suggest to declare a macro for it at the
>> beginning of vivi.c file, with some comment explaining the rationale of the choose,
>> and what else needs to be changed, if this changes (e. g. less than 1ms would require
>> changing the image generation logic, to avoid producing frames with equal content).
>
> Maybe something like this? (please note, I'm not a good text writer. If
> this needs adjustment please help me shape the text up)
>
>
> diff --git a/drivers/media/platform/vivi.c b/drivers/media/platform/vivi.c
> index 5d1b374..45b8a81 100644
> --- a/drivers/media/platform/vivi.c
> +++ b/drivers/media/platform/vivi.c
> @@ -36,6 +36,18 @@
>
>   #define VIVI_MODULE_NAME "vivi"
>
> +/* Maximum allowed frame rate
> + *
> + * Vivi will allow setting timeperframe in [1/FPS_MAX - FPS_MAX/1] range.
> + *
> + * Ideally FPS_MAX should be infinity, i.e. practically UINT_MAX, but that
> + * might hit application errors when they manipulate these values.
> + *
> + * Besides, for tpf < 1ms image-generation logic should be changed, to avoid
> + * producing frames with equal content.
> + */
> +#define FPS_MAX 1000
> +
>   #define MAX_WIDTH 1920
>   #define MAX_HEIGHT 1200
>
> @@ -67,8 +79,8 @@ static const u8 *font8x16;
>
>   /* timeperframe: min/max and default */
>   static const struct v4l2_fract
> -	tpf_min     = {.numerator = 1,		.denominator = UINT_MAX},  /* 1/infty */
> -	tpf_max     = {.numerator = UINT_MAX,	.denominator = 1},         /* infty */
> +	tpf_min     = {.numerator = 1,		.denominator = FPS_MAX},   /* ~1/infty */
> +	tpf_max     = {.numerator = FPS_MAX,	.denominator = 1},         /* ~infty */
>   	tpf_default = {.numerator = 1001,	.denominator = 30000};     /* NTSC */
>
>   #define dprintk(dev, level, fmt, arg...) \

seems OK to me.

Regards,
Mauro

>