This change adds support for display color dithering configuration in
the display control structure. Two dithering modes are possible:
ordered and error-diffusion mode. Error-diffusion dithering is usually
considered higher quality, but can only be used when the active region
is less than 640 pixels wide.
This is based on patches from Chao Jiang <chaoj@xxxxxxxxxx>
Signed-off-by: Robert Morell <rmorell@xxxxxxxxxx>
---
Version 2 adds a default case and removes redundant BUG_ON().
arch/arm/mach-tegra/include/mach/dc.h | 7 +++++++
drivers/video/tegra/dc/dc.c | 24 ++++++++++++++++++++++++
2 files changed, 31 insertions(+), 0 deletions(-)
diff --git a/arch/arm/mach-tegra/include/mach/dc.h b/arch/arm/mach-tegra/include/mach/dc.h
index 254b732..696e6ed 100644
--- a/arch/arm/mach-tegra/include/mach/dc.h
+++ b/arch/arm/mach-tegra/include/mach/dc.h
@@ -44,6 +44,12 @@ enum {
TEGRA_DC_OUT_HDMI,
};
+enum {
+ TEGRA_DC_DISABLE_DITHER = 1,
+ TEGRA_DC_ORDERED_DITHER,
+ TEGRA_DC_ERRDIFF_DITHER,
+};
+
struct tegra_dc_out {
int type;
unsigned flags;
@@ -58,6 +64,7 @@ struct tegra_dc_out {
unsigned order;
unsigned align;
unsigned depth;
+ unsigned dither;
struct tegra_dc_mode *modes;
int n_modes;
diff --git a/drivers/video/tegra/dc/dc.c b/drivers/video/tegra/dc/dc.c
index 16789c2..658cabd 100644
--- a/drivers/video/tegra/dc/dc.c
+++ b/drivers/video/tegra/dc/dc.c
@@ -890,6 +890,30 @@ static void tegra_dc_set_color_control(struct tegra_dc *dc)
break;
}
+ /*
+ * The line buffer for error-diffusion dither is limited to 640 pixels
+ * per line, so we can't use it if the active region is larger than 640
+ * pixels. Be nice and fall back to ordered dithering, but warn so the
+ * platform data can be corrected.
+ */
+ if (WARN_ON(dc->out->dither == TEGRA_DC_ERRDIFF_DITHER &&
+ dc->mode.h_active > 640)) {
+ dc->out->dither = TEGRA_DC_ORDERED_DITHER;
+ }
+
+ switch (dc->out->dither) {
+ default:
+ case TEGRA_DC_DISABLE_DITHER:
+ color_control |= DITHER_CONTROL_DISABLE;
+ break;
+ case TEGRA_DC_ORDERED_DITHER:
+ color_control |= DITHER_CONTROL_ORDERED;
+ break;
+ case TEGRA_DC_ERRDIFF_DITHER:
+ color_control |= DITHER_CONTROL_ERRDIFF;
+ break;
+ }
+
tegra_dc_writel(dc, color_control, DC_DISP_DISP_COLOR_CONTROL);
}
--
1.7.3.4
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