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media: staging: ipu3-imgu: Fix BNR wb gain documentation

Message ID 20220617084519.32129-1-jeanmichel.hautbois@ideasonboard.com
State Accepted
Commit 4b7444ff13250d2b10e940978bd72aef7a5561f2
Headers show
Series media: staging: ipu3-imgu: Fix BNR wb gain documentation | expand

Commit Message

Jean-Michel Hautbois June 17, 2022, 8:45 a.m. UTC 
The documentation states that the BNR factor is a multiplier coded as
u3.13 and with a range of (0, 8). This is not correct, as the isp is
adding 1.0 to the gain applied, ie Pout = { Pin * (1 + Gx) }.

It means that a gain of 1.0 should be coded as 0.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
---
 drivers/staging/media/ipu3/include/uapi/intel-ipu3.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
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Patch

diff --git a/drivers/staging/media/ipu3/include/uapi/intel-ipu3.h b/drivers/staging/media/ipu3/include/uapi/intel-ipu3.h
index dbdd015ce220..caa358e0bae4 100644
--- a/drivers/staging/media/ipu3/include/uapi/intel-ipu3.h
+++ b/drivers/staging/media/ipu3/include/uapi/intel-ipu3.h
@@ -626,8 +626,11 @@  struct ipu3_uapi_stats_3a {
  * @b:	white balance gain for B channel.
  * @gb:	white balance gain for Gb channel.
  *
- * Precision u3.13, range [0, 8). White balance correction is done by applying
- * a multiplicative gain to each color channels prior to BNR.
+ * For BNR parameters WB gain factor for the three channels [Ggr, Ggb, Gb, Gr].
+ * Their precision is U3.13 and the range is (0, 8) and the actual gain is
+ * Gx + 1, it is typically Gx = 1.
+ *
+ * Pout = {Pin * (1 + Gx)}.
  */
 struct ipu3_uapi_bnr_static_config_wb_gains_config {
 	__u16 gr;