Add a new helper function drm_color_ctm_s31_32_to_qm_n() for driver to
convert S31.32 sign-magnitude to Qm.n 2's complement that supported by
hardware.
V4: Address Mihai, Daniel and Ilia's review comments.
V5: Includes the sign bit in the value of m (Qm.n).
V6: Allows m = 0 according to Mihail's comments.
V7: Address Mihail's comments.
V8: Use type 'u32' to replace 'uint32_t'
V9: Rebase.
Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@xxxxxxx>
Reviewed-by: Mihail Atanassov <mihail.atanassov@xxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
drivers/gpu/drm/drm_color_mgmt.c | 34 ++++++++++++++++++++++++++++++++
include/drm/drm_color_mgmt.h | 1 +
2 files changed, 35 insertions(+)
diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index 4ce5c6d8de99..ba71e3b827f1 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -132,6 +132,40 @@ uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision)
}
EXPORT_SYMBOL(drm_color_lut_extract);
+/**
+ * drm_color_ctm_s31_32_to_qm_n
+ *
+ * @user_input: input value
+ * @m: number of integer bits, only support m <= 32, include the sign-bit
+ * @n: number of fractional bits, only support n <= 32
+ *
+ * Convert and clamp S31.32 sign-magnitude to Qm.n (signed 2's complement).
+ * The sign-bit BIT(m+n-1) and above are 0 for positive value and 1 for negative
+ * the range of value is [-2^(m-1), 2^(m-1) - 2^-n]
+ *
+ * For example
+ * A Q3.12 format number:
+ * - required bit: 3 + 12 = 15bits
+ * - range: [-2^2, 2^2 - 2^−15]
+ *
+ * NOTE: the m can be zero if all bit_precision are used to present fractional
+ * bits like Q0.32
+ */
+u64 drm_color_ctm_s31_32_to_qm_n(u64 user_input, u32 m, u32 n)
+{
+ u64 mag = (user_input & ~BIT_ULL(63)) >> (32 - n);
+ bool negative = !!(user_input & BIT_ULL(63));
+ s64 val;
+
+ WARN_ON(m > 32 || n > 32);
+
+ val = clamp_val(mag, 0, negative ?
+ BIT_ULL(n + m - 1) : BIT_ULL(n + m - 1) - 1);
+
+ return negative ? -val : val;
+}
+EXPORT_SYMBOL(drm_color_ctm_s31_32_to_qm_n);
+
/**
* drm_crtc_enable_color_mgmt - enable color management properties
* @crtc: DRM CRTC
diff --git a/include/drm/drm_color_mgmt.h b/include/drm/drm_color_mgmt.h
index d1c662d92ab7..997a42ab29f5 100644
--- a/include/drm/drm_color_mgmt.h
+++ b/include/drm/drm_color_mgmt.h
@@ -30,6 +30,7 @@ struct drm_crtc;
struct drm_plane;
uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision);
+u64 drm_color_ctm_s31_32_to_qm_n(u64 user_input, u32 m, u32 n);
void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
uint degamma_lut_size,
--
2.20.1
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