From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
This function is is there to help driver writers.
Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_crtc_helper.c | 47 +++++++++++++++++++++++++++++++++++++
include/drm/drm_crtc_helper.h | 3 ++
2 files changed, 50 insertions(+), 0 deletions(-)
diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 0153187..341f05c 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -1479,3 +1479,50 @@ void drm_plane_opts_defaults(struct drm_plane_opts *opts)
opts->const_alpha = 0xffff;
}
EXPORT_SYMBOL(drm_plane_opts_defaults);
+
+/**
+ * drm_chroma_phase_offsets - calculate the chroma phase offsets
+ * @ret_xoff: returned horizontal offset (16.16)
+ * @ret_yoff: returned vertical offset (16.16)
+ * @hsub: horizontal chroma subsampling factor
+ * @vsub: vertical chroma subsampling factor
+ * @chroma: chroma siting information
+ * @second_chroma_plane: first or second chroma plane?
+ *
+ * Calculates the phase offset between chroma and luma pixel centers,
+ * based on infromation provided in @chroma, @hsub, @vsub, and
+ * @second_chroma_plane.
+ *
+ * RETURNS:
+ * The chroma phase offsets in 16.16 format. The returned
+ * phase offsets are in chroma (ie. subsampled) coordinate space.
+ */
+void drm_chroma_phase_offsets(int *ret_xoff, int *ret_yoff,
+ int hsub, int vsub, uint8_t chroma_siting,
+ bool second_chroma_plane)
+{
+ *ret_xoff = 0;
+ *ret_yoff = 0;
+
+ switch (chroma_siting & 0x3) {
+ case DRM_CHROMA_SITING_HORZ_LEFT:
+ break;
+ case DRM_CHROMA_SITING_HORZ_CENTER:
+ *ret_xoff -= (hsub - 1) * 0x8000 / hsub;
+ break;
+ }
+
+ switch (chroma_siting & 0xc0) {
+ case DRM_CHROMA_SITING_VERT_TOP:
+ break;
+ case DRM_CHROMA_SITING_VERT_CENTER:
+ *ret_yoff -= (vsub - 1) * 0x8000 / vsub;
+ break;
+ }
+
+ /* Chroma planes out of phase by 0.5 chroma lines? */
+ if (second_chroma_plane &&
+ (chroma_siting & DRM_CHROMA_SITING_MISALIGNED_PLANES))
+ *ret_yoff -= 0x8000;
+}
+EXPORT_SYMBOL(drm_chroma_phase_offsets);
diff --git a/include/drm/drm_crtc_helper.h b/include/drm/drm_crtc_helper.h
index e4946a5..58881f6 100644
--- a/include/drm/drm_crtc_helper.h
+++ b/include/drm/drm_crtc_helper.h
@@ -180,5 +180,8 @@ extern int drm_calc_hscale(struct drm_region *src, struct drm_region *dst,
extern int drm_calc_vscale(struct drm_region *src, struct drm_region *dst,
int min_vscale, int max_vscale);
extern void drm_plane_opts_defaults(struct drm_plane_opts *opts);
+extern void drm_chroma_phase_offsets(int *ret_xoff, int *ret_yoff,
+ int hsub, int vsub, uint8_t chroma_siting,
+ bool second_chroma_plane);
#endif
--
1.7.3.4
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