[v6,1/4] drm: Add a new helper drm_color_ctm_s31_32_to_qm_n()

Commit Message

James Qian Wang Oct. 21, 2019, 7:23 a.m. UTC

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.

Signed-off-by: james qian wang (Arm Technology China) <[e-mail]>
Reviewed-by: Mihail Atanassov <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
---
 drivers/gpu/drm/drm_color_mgmt.c | 36 ++++++++++++++++++++++++++++++++
 include/drm/drm_color_mgmt.h     |  2 ++
 2 files changed, 38 insertions(+)

--
2.20.1

Patch

diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index 4ce5c6d8de99..0f833470d049 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -132,6 +132,42 @@  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
+ * higher bits that above m + n are cleared or equal to sign-bit BIT(m+n).
+ * 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
+ */
+uint64_t drm_color_ctm_s31_32_to_qm_n(uint64_t user_input,
+				      uint32_t m, uint32_t 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..60fea5501886 100644
--- a/include/drm/drm_color_mgmt.h
+++ b/include/drm/drm_color_mgmt.h
@@ -30,6 +30,8 @@  struct drm_crtc;
 struct drm_plane;

 uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision);
+uint64_t drm_color_ctm_s31_32_to_qm_n(uint64_t user_input,
+				      uint32_t m, uint32_t n);

 void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
 				uint degamma_lut_size,