[PATCH v3 10/10] media: microchip-isc: fix WB offset and gain register field masking

[Balakrishnan Sambath]

ISC_WB_O_* and ISC_WB_G_* each pack two 13-bit fields. A negative offset
sign-extends and corrupts the adjacent field. Add masks for the two
fields and write them with FIELD_PREP(), which masks each value into its
field, so sign extension can no longer bleed across.

Fixes: 91b4e487b0c6 ("media: microchip: add ISC driver as Microchip ISC")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Balakrishnan Sambath <balakrishnan.s@xxxxxxxxxxxxx>
---
 .../media/platform/microchip/microchip-isc-base.c   | 21 +++++++++++++--------
 .../media/platform/microchip/microchip-isc-regs.h   |  6 ++++++
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/media/platform/microchip/microchip-isc-base.c b/drivers/media/platform/microchip/microchip-isc-base.c
index 1a9b97edfa32..3d25d7d28652 100644
--- a/drivers/media/platform/microchip/microchip-isc-base.c
+++ b/drivers/media/platform/microchip/microchip-isc-base.c
@@ -62,18 +62,23 @@ static inline void isc_update_awb_ctrls(struct isc_device *isc)
 
 	/* In here we set our actual hw pipeline config */
 
+	/*
+	 * Each register packs two 13-bit fields. FIELD_PREP() masks every
+	 * value into its field, so sign extension of a negative offset can
+	 * no longer bleed into the adjacent field.
+	 */
 	regmap_write(isc->regmap, ISC_WB_O_RGR,
-		     ((ctrls->offset[ISC_HIS_CFG_MODE_R])) |
-		     ((ctrls->offset[ISC_HIS_CFG_MODE_GR]) << 16));
+		     FIELD_PREP(ISC_WB_O_LO, ctrls->offset[ISC_HIS_CFG_MODE_R]) |
+		     FIELD_PREP(ISC_WB_O_HI, ctrls->offset[ISC_HIS_CFG_MODE_GR]));
 	regmap_write(isc->regmap, ISC_WB_O_BGB,
-		     ((ctrls->offset[ISC_HIS_CFG_MODE_B])) |
-		     ((ctrls->offset[ISC_HIS_CFG_MODE_GB]) << 16));
+		     FIELD_PREP(ISC_WB_O_LO, ctrls->offset[ISC_HIS_CFG_MODE_B]) |
+		     FIELD_PREP(ISC_WB_O_HI, ctrls->offset[ISC_HIS_CFG_MODE_GB]));
 	regmap_write(isc->regmap, ISC_WB_G_RGR,
-		     ctrls->gain[ISC_HIS_CFG_MODE_R] |
-		     (ctrls->gain[ISC_HIS_CFG_MODE_GR] << 16));
+		     FIELD_PREP(ISC_WB_G_LO, ctrls->gain[ISC_HIS_CFG_MODE_R]) |
+		     FIELD_PREP(ISC_WB_G_HI, ctrls->gain[ISC_HIS_CFG_MODE_GR]));
 	regmap_write(isc->regmap, ISC_WB_G_BGB,
-		     ctrls->gain[ISC_HIS_CFG_MODE_B] |
-		     (ctrls->gain[ISC_HIS_CFG_MODE_GB] << 16));
+		     FIELD_PREP(ISC_WB_G_LO, ctrls->gain[ISC_HIS_CFG_MODE_B]) |
+		     FIELD_PREP(ISC_WB_G_HI, ctrls->gain[ISC_HIS_CFG_MODE_GB]));
 }
 
 static inline void isc_reset_awb_ctrls(struct isc_device *isc)
diff --git a/drivers/media/platform/microchip/microchip-isc-regs.h b/drivers/media/platform/microchip/microchip-isc-regs.h
index 9ddbbb6dd68b..fe145b142b82 100644
--- a/drivers/media/platform/microchip/microchip-isc-regs.h
+++ b/drivers/media/platform/microchip/microchip-isc-regs.h
@@ -149,6 +149,12 @@
 /* ISC White Balance Gain for B, GB Register */
 #define ISC_WB_G_BGB	0x0000006c
 
+/* Each WB offset/gain register packs two 13-bit fields, low and high */
+#define ISC_WB_O_LO	GENMASK(12, 0)	/* R or B  offset [12:0]  */
+#define ISC_WB_O_HI	GENMASK(28, 16)	/* GR or GB offset [28:16] */
+#define ISC_WB_G_LO	GENMASK(12, 0)	/* R or B  gain [12:0]  */
+#define ISC_WB_G_HI	GENMASK(28, 16)	/* GR or GB gain [28:16] */
+
 /* ISC Color Filter Array Control Register */
 #define ISC_CFA_CTRL    0x00000070
 

-- 
2.34.1