[PATCH] media: rkisp1: correct histogram window size

[Krzysztof Hałasa]

The histogram window dimensions are unnecessarily decremented. This can be
seen in the following example, where when all pixels are of maximum intensity
there are pixels that we expect to be counted but are missing from the highest
bin. Fix this by removing the unnecessary decrement.

Without the patch (i.MX8MP, all-white RGGB-12 full HD input from
the sensor, YUV NV12 output from ISP, full range, histogram Y mode).
HIST_STEPSIZE = 3 (lowest permitted), all weights are set to 1:

isp_hist_h_size: 383 (= 1920 / 5 - 1)
isp_hist_v_size: 215 (= 1080 / 5 - 1)
histogram_measurement_result[16]: 0 0 0 0  0 0 0 0  0 0 0 0  0 0 0 229401

Apparently the histogram is missing the last column (3-pixel wide,
though only single pixels count) and the last (same idea) row
of the input image: 1917 * 1077 / 3 / 3 = 229401.

E.g. without the patch, the pixels counted in lines are:
0, 3, ... 1914 (which makes 1917/3), and patched:
0, 3, ... 1914, 1917 (which makes 1920/3).
The same is true for rows.

With the patch applied:
isp_hist_h_size: 384 (= 1920 / 5)
isp_hist_v_size: 216 (= 1080 / 5)
histogram_measurement_result[16]: 0 0 0 0  0 0 0 0  0 0 0 0  0 0 0 230400

1920 * 1080 / 3 / 3 = 230400

Signed-off-by: Krzysztof Hałasa <khalasa at piap.pl>
Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>

diff --git a/drivers/media/platform/rockchip/rkisp1/rkisp1-params.c b/drivers/media/platform/rockchip/rkisp1/rkisp1-params.c
index b28f4140c8a3..ca9b3e711e5f 100644
--- a/drivers/media/platform/rockchip/rkisp1/rkisp1-params.c
+++ b/drivers/media/platform/rockchip/rkisp1/rkisp1-params.c
@@ -819,8 +819,8 @@ static void rkisp1_hst_config_v10(struct rkisp1_params *params,
 		     arg->meas_window.v_offs);
 
 	block_hsize = arg->meas_window.h_size /
-		      RKISP1_CIF_ISP_HIST_COLUMN_NUM_V10 - 1;
-	block_vsize = arg->meas_window.v_size / RKISP1_CIF_ISP_HIST_ROW_NUM_V10 - 1;
+		      RKISP1_CIF_ISP_HIST_COLUMN_NUM_V10;
+	block_vsize = arg->meas_window.v_size / RKISP1_CIF_ISP_HIST_ROW_NUM_V10;
 
 	rkisp1_write(params->rkisp1, RKISP1_CIF_ISP_HIST_H_SIZE_V10,
 		     block_hsize);

-- 
Krzysztof "Chris" Hałasa

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