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Commit c3e75c7d authored by Martin Bugge's avatar Martin Bugge Committed by Mauro Carvalho Chehab
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[media] v4l2-dv-timings: fix CVT calculation 



This patch fixes two errors that caused incorrect format detections:
The first bug is in the calculation of the vertical backporch: the combined
period of vsync and backporch must *exceed* a certain minimum value, and not
be equal to it.
The second bug is a rounding error in the reduced blanking calculation:
expand the ideal_duty_cylce to be in parts per ten thousand to avoid
rounding errors.

Signed-off-by: default avatarMartin Bugge <marbugge@cisco.com>
Cc: Mats Randgaard <matrandg@cisco.com>
Signed-off-by: default avatarHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: default avatarMauro Carvalho Chehab <m.chehab@samsung.com>
parent 1056e438

drivers/media/v4l2-core/v4l2-dv-timings.c

+9 −10
Original line number Diff line number Diff line
@@ -286,14 +286,14 @@ bool v4l2_detect_cvt(unsigned frame_height, unsigned hfreq, unsigned vsync, 
	/* Vertical */

	if (reduced_blanking) {

		v_fp = CVT_RB_V_FPORCH;

		v_bp = (CVT_RB_MIN_V_BLANK * hfreq + 999999) / 1000000;

		v_bp = (CVT_RB_MIN_V_BLANK * hfreq + 1999999) / 1000000;

		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 + 999999) / 1000000 - vsync;

		v_bp = (CVT_MIN_VSYNC_BP * hfreq + 1999999) / 1000000 - vsync;



		if (v_bp < CVT_MIN_V_BPORCH)

			v_bp = CVT_MIN_V_BPORCH;
@@ -337,17 +337,16 @@ bool v4l2_detect_cvt(unsigned frame_height, unsigned hfreq, unsigned vsync, 


		frame_width = image_width + CVT_RB_H_BLANK;

	} else {

		unsigned ideal_duty_cycle_per_myriad =

			100 * CVT_C_PRIME - (CVT_M_PRIME * 100000) / hfreq;

		int h_blank;

		unsigned ideal_duty_cycle = CVT_C_PRIME - (CVT_M_PRIME * 1000) / hfreq;



		h_blank = (image_width * ideal_duty_cycle + (100 - ideal_duty_cycle) / 2) /

						(100 - ideal_duty_cycle);

		h_blank = h_blank - h_blank % (2 * CVT_CELL_GRAN);

		if (ideal_duty_cycle_per_myriad < 2000)

			ideal_duty_cycle_per_myriad = 2000;



		if (h_blank * 100 / image_width < 20) {

			h_blank = image_width / 5;

			h_blank = (h_blank + 0x7) & ~0x7;

		}

		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;



		pix_clk = (image_width + h_blank) * hfreq;

		pix_clk = (pix_clk / CVT_PXL_CLK_GRAN) * CVT_PXL_CLK_GRAN;