From: Carsten Haitzler <carsten.haitz...@arm.com>
When setting up a readback connector that writes data back to memory
rather than to an actual output device (HDMI etc.), rounding was set
to round. As the DPU uses a higher internal number of bits when generating
a color value, this round-down back to 8bit ended up with everything
being off-by one. e.g. #fefefe became #ffffff. This sets
rounding to "round-down" so things end up correct by turning on the LW_TRC
round down flag.
Signed-off-by: Carsten Haitzler <carsten.haitz...@arm.com>
---
drivers/gpu/drm/arm/display/komeda/d71/d71_component.c | 7 ++++++-
drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h | 1 +
2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/arm/display/komeda/d71/d71_component.c
b/drivers/gpu/drm/arm/display/komeda/d71/d71_component.c
index 8a02ade369db..e97acc5519d1 100644
--- a/drivers/gpu/drm/arm/display/komeda/d71/d71_component.c
+++ b/drivers/gpu/drm/arm/display/komeda/d71/d71_component.c
@@ -468,7 +468,12 @@ static void d71_wb_layer_update(struct komeda_component *c,
struct komeda_layer_state *st = to_layer_st(state);
struct drm_connector_state *conn_st = state->wb_conn->state;
struct komeda_fb *kfb = to_kfb(conn_st->writeback_job->fb);
- u32 ctrl = L_EN | LW_OFM, mask = L_EN | LW_OFM | LW_TBU_EN;
+ /* LW_TRC sets rounding to truncate not round which is needed for
+ * the output of writeback to match the input in the most common
+ * use cases like RGB888 -> RGB888, so set this bit by default
+ */
+ u32 ctrl = LW_TRC | L_EN | LW_OFM;
+ u32 mask = LW_TRC | L_EN | LW_OFM | LW_TBU_EN;
u32 __iomem *reg = c->reg;
d71_layer_update_fb(c, kfb, st->addr);
diff --git a/drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h
b/drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h
index e80172a0b320..a8036689d721 100644
--- a/drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h
+++ b/drivers/gpu/drm/arm/display/komeda/d71/d71_regs.h
@@ -321,6 +321,7 @@
#define LAYER_WR_FORMAT 0x0D8
/* Layer_WR control bits */
+#define LW_TRC BIT(1)
#define LW_OFM BIT(4)
#define LW_LALPHA(x) (((x) & 0xFF) << 8)
#define LW_A_WCACHE(x) (((x) & 0xF) << 28)
--
2.30.0
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