[PATCH v5 12/12] media: microchip-isc: scale DPC black level to sensor bit depth

[Balakrishnan Sambath]

The DPC_BLCFG black level register expects counts in the sensor's
native bit depth. The previous fixed 10-bit value (64 counts) under-
corrects 12-bit sensors and over-corrects 8-bit ones, producing an
incorrect black point. Scale the nominal 10-bit value to match the
8/10/12-bit sensor bus width derived from pfe_cfg0_bps.

Co-developed-by: Balamanikandan Gunasundar <balamanikandan.gunasundar@xxxxxxxxxxxxx>
Signed-off-by: Balamanikandan Gunasundar <balamanikandan.gunasundar@xxxxxxxxxxxxx>
Signed-off-by: Balakrishnan Sambath <balakrishnan.s@xxxxxxxxxxxxx>
---
 .../media/platform/microchip/microchip-sama7g5-isc.c  | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/microchip/microchip-sama7g5-isc.c b/drivers/media/platform/microchip/microchip-sama7g5-isc.c
index f51c7cac25df..067a6e1558d3 100644
--- a/drivers/media/platform/microchip/microchip-sama7g5-isc.c
+++ b/drivers/media/platform/microchip/microchip-sama7g5-isc.c
@@ -26,6 +26,7 @@
  * HIS: Histogram module performs statistic counters on the frames
  */
 
+#include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/clkdev.h>
 #include <linux/clk-provider.h>
@@ -289,9 +290,25 @@ static void isc_sama7g5_config_dpc(struct isc_device *isc)
 {
 	u32 bay_cfg = isc->config.sd_format->cfa_baycfg;
 	struct regmap *regmap = isc->regmap;
+	u32 bps, bloff;
+
+	/*
+	 * Scale the nominal 10-bit black level offset (64 counts) to the
+	 * actual sensor bus width.
+	 * ISC_PFE_CFG0_BPS encodes (12 - bit_depth) / 2 in bits[30:28]:
+	 *   BPS_EIGHT  = 4  ->  8-bit  -> bloff = 64 >> 2 = 16
+	 *   BPS_TEN    = 2  -> 10-bit  -> bloff = 64
+	 *   BPS_TWELVE = 0  -> 12-bit  -> bloff = min(64 << 2, 255) = 255
+	 * The BLOFF hardware field is 8-bit so values are clamped to 255.
+	 */
+	bps = FIELD_GET(ISC_PFE_CFG0_BPS_MASK, isc->config.sd_format->pfe_cfg0_bps);
+	if (bps >= 2)
+		bloff = 64u >> (bps - 2);
+	else
+		bloff = min(64u << (2 - bps), 255u);
 
 	regmap_update_bits(regmap, ISC_DPC_CFG, ISC_DPC_CFG_BLOFF_MASK,
-			   (64 << ISC_DPC_CFG_BLOFF_SHIFT));
+			   (bloff << ISC_DPC_CFG_BLOFF_SHIFT));
 	regmap_update_bits(regmap, ISC_DPC_CFG, ISC_DPC_CFG_BAYCFG_MASK,
 			   (bay_cfg << ISC_DPC_CFG_BAYCFG_SHIFT));
 }

-- 
2.34.1