Re: [RFC PATCH] v4l2-dv-timings: add support for reduced blanking v2

Prashant Laddha (prladdha)
2015-06-08T11:34:10Z

Thanks for the review Hans. I will address your comments and post revised
patches for this.

Regards,
Prashant

On 08/06/15 4:14 pm, "Hans Verkuil" <hverkuil@xs4all.nl> wrote:

>On 06/05/2015 10:52 AM, Prashant Laddha wrote:
>> Added support for reduced blanking version 2 (RB v2) in cvt timings.
>> Standard specifies a fixed vsync pulse of 8 lines to indicate RB v2
>> timings. Vertical back porch is fixed at 6 lines and vertical front
>> porch is remainder of vertical blanking time.
>>
>> For Rb v2, horizontal blanking is fixed at 80 pixels. Horizontal sync
>> is fixed at 32. All horizontal timing counts (active pixels, front,
>> back porches) can be specified upto a precision of 1.
>>
>> To Do: Pass aspect ratio information to v4l2_detect_cvt()
>> RB v2 allows for non standard aspect ratios. In RB v2 vsync does not
>> indicate aspect ratio. In the absence of aspect ratio information,
>> v4l2_detect_cvt() cannot calculate image width from image height.
>
>Reading the CVT spec I see that RB v2 assumes that the pixel aspect ratio
>is always square (section 3.4.3, item 7 says that the aspect ratio is
>to be derived from the active video resolution, which is only possible
>if the pixel aspect ratio is square.
>
>So I would suggest adding a 'frame_width' argument to v4l2_detect_cvt:
>this
>will be used in the v2 case. If RB v2 is detected and frame_width is 0,
>then
>v4l2_detect_cvt will return false.
>
>Since RB v2 is something we'll only see with digital video interfaces
>where
>we always know the horizontal active video, this shouldn't be a problem.
>
>Some code comments below:
>
>>
>> Cc: Hans Verkuil <hans.verkuil@cisco.com>
>> Signed-off-by: Prashant Laddha <prladdha@cisco.com>
>> ---
>> drivers/media/v4l2-core/v4l2-dv-timings.c | 72
>>+++++++++++++++++++++++--------
>> 1 file changed, 54 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-dv-timings.c
>>b/drivers/media/v4l2-core/v4l2-dv-timings.c
>> index 0d849fc..4efc6f6 100644
>> --- a/drivers/media/v4l2-core/v4l2-dv-timings.c
>> +++ b/drivers/media/v4l2-core/v4l2-dv-timings.c
>> @@ -309,6 +309,7 @@ EXPORT_SYMBOL_GPL(v4l2_print_dv_timings);
>> */
>>
>> #define CVT_PXL_CLK_GRAN 250000 /* pixel clock granularity */
>> +#define CVT_PXL_CLK_GRAN_RB_V2 1000 /* granularity for reduced
>>blanking v2*/
>>
>> /* Normal blanking */
>> #define CVT_MIN_V_BPORCH 7 /* lines */
>> @@ -328,10 +329,14 @@ EXPORT_SYMBOL_GPL(v4l2_print_dv_timings);
>> /* Reduced Blanking */
>> #define CVT_RB_MIN_V_BPORCH 7 /* lines */
>> #define CVT_RB_V_FPORCH 3 /* lines */
>> -#define CVT_RB_MIN_V_BLANK 460 /* us */
>> +#define CVT_RB_MIN_V_BLANK 460 /* us */
>> #define CVT_RB_H_SYNC 32 /* pixels */
>> -#define CVT_RB_H_BPORCH 80 /* pixels */
>> #define CVT_RB_H_BLANK 160 /* pixels */
>> +/* Reduce blanking Version 2 */
>> +#define CVT_RB_V2_H_BLANK 80 /* pixels */
>> +#define CVT_RB_MIN_V_FPORCH 3 /* lines */
>> +#define CVT_RB_V2_MIN_V_FPORCH 1 /* lines */
>> +#define CVT_RB_V_BPORCH 6 /* lines */
>>
>> /** v4l2_detect_cvt - detect if the given timings follow the CVT
>>standard
>> * @frame_height - the total height of the frame (including blanking)
>>in lines.
>> @@ -356,9 +361,10 @@ bool v4l2_detect_cvt(unsigned frame_height,
>>unsigned hfreq, unsigned vsync,
>> int v_fp, v_bp, h_fp, h_bp, hsync;
>> int frame_width, image_height, image_width;
>> bool reduced_blanking;
>> + bool rb_v2 = false;
>> unsigned pix_clk;
>>
>> - if (vsync < 4 || vsync > 7)
>> + if (vsync < 4 || vsync > 8)
>> return false;
>>
>> if (polarities == V4L2_DV_VSYNC_POS_POL)
>> @@ -368,17 +374,32 @@ bool v4l2_detect_cvt(unsigned frame_height,
>>unsigned hfreq, unsigned vsync,
>> else
>> return false;
>>
>> + if (reduced_blanking && vsync == 8)
>> + rb_v2 = true;
>> +
>> + if (!rb_v2 && vsync > 7)
>> + return false;
>> +
>> if (hfreq == 0)
>> return false;
>>
>> /* Vertical */
>> if (reduced_blanking) {
>> - v_fp = CVT_RB_V_FPORCH;
>> - v_bp = (CVT_RB_MIN_V_BLANK * hfreq) / 1000000 + 1;
>> - v_bp -= vsync + v_fp;
>> -
>> - if (v_bp < CVT_RB_MIN_V_BPORCH)
>> - v_bp = CVT_RB_MIN_V_BPORCH;
>> + if (rb_v2) {
>> + v_bp = CVT_RB_V_BPORCH;
>> + v_fp = (CVT_RB_MIN_V_BLANK * hfreq) / 1000000 + 1;
>> + v_fp -= vsync + v_bp;
>> +
>> + if (v_fp < CVT_RB_V2_MIN_V_FPORCH)
>> + v_fp = CVT_RB_V2_MIN_V_FPORCH;
>> + } else {
>> + v_fp = CVT_RB_V_FPORCH;
>> + v_bp = (CVT_RB_MIN_V_BLANK * hfreq) / 1000000 + 1;
>> + v_bp -= vsync + v_fp;
>> +
>> + if (v_bp < CVT_RB_MIN_V_BPORCH)
>> + v_bp = CVT_RB_MIN_V_BPORCH;
>> + }
>> } else {
>> v_fp = CVT_MIN_V_PORCH_RND;
>> v_bp = (CVT_MIN_VSYNC_BP * hfreq) / 1000000 + 1 - vsync;
>> @@ -415,22 +436,40 @@ bool v4l2_detect_cvt(unsigned frame_height,
>>unsigned hfreq, unsigned vsync,
>> else
>> return false;
>> break;
>> + case 8:
>> + /* To Do:
>> + * For Reduced Blanking v2, vsync does not indicate aspect ratio and
>> + * hence can not be used to derive image width. In such a case, either
>> + * aspect ratio information or image width should be supplied to
>> + * v4l2_detect_cvt(). This would need API change. As of now assuming
>> + * 16:9 as default aspect ratio.
>> + * */
>> + image_width = (image_height * 16) / 9;
>> + break;
>> default:
>> return false;
>> }
>>
>> - image_width = image_width & ~7;
>> + if (!rb_v2)
>> + image_width = image_width & ~7;
>>
>> /* Horizontal */
>> if (reduced_blanking) {
>> - pix_clk = (image_width + CVT_RB_H_BLANK) * hfreq;
>> - pix_clk = (pix_clk / CVT_PXL_CLK_GRAN) * CVT_PXL_CLK_GRAN;
>> + int h_blank;
>>
>> - h_bp = CVT_RB_H_BPORCH;
>> + if (rb_v2)
>> + h_blank = CVT_RB_V2_H_BLANK;
>> + else
>> + h_blank = CVT_RB_H_BLANK;
>
>I prefer: h_blank = rb_v2 ? CVT_RB_V2_H_BLANK : CVT_RB_H_BLANK
>
>> +
>> + pix_clk = (image_width + h_blank) * hfreq;
>> + pix_clk = (pix_clk / CVT_PXL_CLK_GRAN_RB_V2) *
>>CVT_PXL_CLK_GRAN_RB_V2;
>
>Shouldn't the granularity be dependent on rb_v2?
>
>> +
>> + h_bp = h_blank / 2;
>> hsync = CVT_RB_H_SYNC;
>> - h_fp = CVT_RB_H_BLANK - h_bp - hsync;
>> + h_fp = h_blank - h_bp - hsync;
>>
>> - frame_width = image_width + CVT_RB_H_BLANK;
>> + frame_width = image_width + h_blank;
>> } else {
>> unsigned ideal_duty_cycle_per_myriad =
>> 100 * CVT_C_PRIME - (CVT_M_PRIME * 100000) / hfreq;
>> @@ -438,11 +477,9 @@ bool v4l2_detect_cvt(unsigned frame_height,
>>unsigned hfreq, unsigned vsync,
>>
>> if (ideal_duty_cycle_per_myriad < 2000)
>> ideal_duty_cycle_per_myriad = 2000;
>> -
>> h_blank = image_width * ideal_duty_cycle_per_myriad /
>> (10000 - ideal_duty_cycle_per_myriad);
>> h_blank = (h_blank / (2 * CVT_CELL_GRAN)) * 2 * CVT_CELL_GRAN;
>> -
>
>Why the spurious whitespace changes?
>
>> pix_clk = (image_width + h_blank) * hfreq;
>> pix_clk = (pix_clk / CVT_PXL_CLK_GRAN) * CVT_PXL_CLK_GRAN;
>>
>> @@ -483,7 +520,6 @@ bool v4l2_detect_cvt(unsigned frame_height,
>>unsigned hfreq, unsigned vsync,
>>
>> if (reduced_blanking)
>> fmt->bt.flags |= V4L2_DV_FL_REDUCED_BLANKING;
>> -
>
>Ditto.
>
>> return true;
>> }
>> EXPORT_SYMBOL_GPL(v4l2_detect_cvt);
>>
>
>Regards,
>
> Hans