[PATCH RFC 3/4] media: qcom: camss: vfe: Add the demux + BLS stage to the pixel pipe
From: William Bright
Date: Tue Oct 13 2026 - 04:49:35 EST
The pixel pipe never subtracts the sensor black level, so blacks come
out lifted and a demosaic that is sensitive to a green pedestal mixes
colours.
Add the demux + BLS block ahead of demosaic as an opt in stage. It
takes the CFA order from the sink format, subtracts a static black
level and stretches the rest back to full scale. Its layout was worked
out on the IFE 780 against CamX's demux + BLS 1.4.1 settings; the
IFE 880 keeps it off until it is checked there.
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: William Bright <william.bright@xxxxxxxxxxx>
---
drivers/media/platform/qcom/camss/camss-vfe-780.c | 3 +-
.../media/platform/qcom/camss/camss-vfe-880-pp.c | 65 +++++++++++++++++++++-
.../media/platform/qcom/camss/camss-vfe-880-pp.h | 3 +-
3 files changed, 68 insertions(+), 3 deletions(-)
diff --git a/drivers/media/platform/qcom/camss/camss-vfe-780.c b/drivers/media/platform/qcom/camss/camss-vfe-780.c
index c2ffe39f929a..032786c4ed74 100644
--- a/drivers/media/platform/qcom/camss/camss-vfe-780.c
+++ b/drivers/media/platform/qcom/camss/camss-vfe-780.c
@@ -247,7 +247,8 @@ static void vfe_line_prepare(struct vfe_line *line)
struct vfe_device *vfe = to_vfe(line);
if (line->is_pix && pix->pixelformat == V4L2_PIX_FMT_NV12)
- vfe_880_setup_pixel_pipe(vfe, vfe_pp_desc(vfe), pix->width, pix->height);
+ vfe_880_setup_pixel_pipe(vfe, vfe_pp_desc(vfe), pix->width, pix->height,
+ line->fmt[MSM_VFE_PAD_SINK].code);
}
static const struct camss_video_ops vfe_video_ops_780 = {
diff --git a/drivers/media/platform/qcom/camss/camss-vfe-880-pp.c b/drivers/media/platform/qcom/camss/camss-vfe-880-pp.c
index f962016ef3c6..87e6a241ec05 100644
--- a/drivers/media/platform/qcom/camss/camss-vfe-880-pp.c
+++ b/drivers/media/platform/qcom/camss/camss-vfe-880-pp.c
@@ -11,6 +11,7 @@
#include <linux/io.h>
#include <linux/kernel.h>
+#include <linux/media-bus-format.h>
#include "camss.h"
#include "camss-vfe.h"
@@ -18,6 +19,17 @@
/* Register offsets, named as in the IFE register map */
#define IFE_TOP_CORE_CFG_0 0x00024
+#define IFE_DEMUX_BLS_MODULE_CFG 0x03b60
+#define IFE_DEMUX_BLS_PERIOD(n) ((n) << 20)
+#define IFE_DEMUX_BLS_EVEN_CFG 0x03b68
+#define IFE_DEMUX_BLS_ODD_CFG 0x03b6c
+#define IFE_DEMUX_BLS_GAIN_CFG_0 0x03b70
+#define IFE_DEMUX_BLS_GAIN_CFG_1 0x03b74
+#define IFE_DEMUX_BLS_SUB_G_EVEN 0x03b78
+#define IFE_DEMUX_BLS_SUB_G_ODD 0x03b7c
+#define IFE_DEMUX_BLS_SUB_B 0x03b80
+#define IFE_DEMUX_BLS_SUB_R 0x03b84
+#define IFE_DEMUX_BLS_SUB(v) ((v) << 20)
#define IFE_WB_GAIN_MODULE_CFG 0x04560
#define IFE_WB_GAIN_WB_CFG_0 0x04568
#define IFE_WB_GAIN_WB_CFG_1 0x0456c
@@ -313,6 +325,55 @@ static void vfe_setup_chroma_downscale_nv12(struct vfe_device *vfe, u32 w, u32 h
writel_relaxed(0x00000000, vfe->base + IFE_DOWNSCALE_MN_C_VID_OUT_DOWNSCALE_MN_C_V_PHASE_CFG);
}
+/* 12 bit black level subtracted ahead of demosaic, 42 at 10 bit */
+#define IFE_780_BLACK_LEVEL 168
+
+/* Demux + BLS: CFA order from the sink format, black level subtracted */
+static void vfe_setup_demux_bls(struct vfe_device *vfe, u32 code)
+{
+ u32 even, odd, gain, bl = IFE_780_BLACK_LEVEL;
+
+ switch (code) {
+ case MEDIA_BUS_FMT_SRGGB8_1X8:
+ case MEDIA_BUS_FMT_SRGGB10_1X10:
+ case MEDIA_BUS_FMT_SRGGB12_1X12:
+ case MEDIA_BUS_FMT_SRGGB14_1X14:
+ even = 0xc9;
+ odd = 0xac;
+ break;
+ case MEDIA_BUS_FMT_SGBRG8_1X8:
+ case MEDIA_BUS_FMT_SGBRG10_1X10:
+ case MEDIA_BUS_FMT_SGBRG12_1X12:
+ case MEDIA_BUS_FMT_SGBRG14_1X14:
+ even = 0xca;
+ odd = 0x9c;
+ break;
+ case MEDIA_BUS_FMT_SBGGR8_1X8:
+ case MEDIA_BUS_FMT_SBGGR10_1X10:
+ case MEDIA_BUS_FMT_SBGGR12_1X12:
+ case MEDIA_BUS_FMT_SBGGR14_1X14:
+ even = 0xac;
+ odd = 0xc9;
+ break;
+ default:
+ even = 0x9c;
+ odd = 0xca;
+ break;
+ }
+
+ gain = DIV_ROUND_CLOSEST(0x400 * 4095, 4095 - bl);
+
+ writel_relaxed(even, vfe->base + IFE_DEMUX_BLS_EVEN_CFG);
+ writel_relaxed(odd, vfe->base + IFE_DEMUX_BLS_ODD_CFG);
+ writel_relaxed(gain << 16 | gain, vfe->base + IFE_DEMUX_BLS_GAIN_CFG_0);
+ writel_relaxed(gain << 16 | gain, vfe->base + IFE_DEMUX_BLS_GAIN_CFG_1);
+ writel_relaxed(IFE_DEMUX_BLS_SUB(bl), vfe->base + IFE_DEMUX_BLS_SUB_G_EVEN);
+ writel_relaxed(IFE_DEMUX_BLS_SUB(bl), vfe->base + IFE_DEMUX_BLS_SUB_G_ODD);
+ writel_relaxed(IFE_DEMUX_BLS_SUB(bl), vfe->base + IFE_DEMUX_BLS_SUB_B);
+ writel_relaxed(IFE_DEMUX_BLS_SUB(bl), vfe->base + IFE_DEMUX_BLS_SUB_R);
+ writel_relaxed(IFE_DEMUX_BLS_PERIOD(1) | 1, vfe->base + IFE_DEMUX_BLS_MODULE_CFG);
+}
+
/* IFE 880: Q10 gain of 4.0 */
const struct vfe_pp_desc vfe_pp_desc_880 = {
.wb_gain = 0x00001000,
@@ -617,9 +678,11 @@ static void vfe_setup_ds16(struct vfe_device *vfe, u32 w, u32 h)
/* Called from vfe_line_prepare() for NV12, ahead of the write masters and the IPP reg update */
void vfe_880_setup_pixel_pipe(struct vfe_device *vfe, const struct vfe_pp_desc *desc,
- u32 w, u32 h)
+ u32 w, u32 h, u32 code)
{
vfe_setup_core_config(vfe);
+ if (desc->demux_bls)
+ vfe_setup_demux_bls(vfe, code);
vfe_setup_chroma_downscale_nv12(vfe, w, h);
vfe_setup_demosaic(vfe, desc);
vfe_setup_color_correction(vfe);
diff --git a/drivers/media/platform/qcom/camss/camss-vfe-880-pp.h b/drivers/media/platform/qcom/camss/camss-vfe-880-pp.h
index fe3a604c579d..0a5ee6d85312 100644
--- a/drivers/media/platform/qcom/camss/camss-vfe-880-pp.h
+++ b/drivers/media/platform/qcom/camss/camss-vfe-880-pp.h
@@ -9,12 +9,13 @@ struct vfe_device;
/* What differs between the IFEs that run this pixel pipe */
struct vfe_pp_desc {
u32 wb_gain; /* WB gain register value for full scale */
+ bool demux_bls; /* subtract the black level in demux + BLS */
};
extern const struct vfe_pp_desc vfe_pp_desc_880;
void vfe_880_setup_pixel_pipe(struct vfe_device *vfe, const struct vfe_pp_desc *desc,
- u32 width, u32 height);
+ u32 width, u32 height, u32 code);
void vfe_880_set_aec_bhist_region(struct vfe_device *vfe, u32 h_offset,
u32 v_offset, u32 h_num, u32 v_num);
--
2.43.0