linux-kernel - [PATCH v6 1/4] drm: Add a new helper drm_color_ctm_s31_32_to_qm

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Message-ID: <20191021072215.3993-2-james.qian.wang@arm.com>
Date:   Mon, 21 Oct 2019 07:23:04 +0000
From:   "james qian wang (Arm Technology China)" <james.qian.wang@....com>
To:     Liviu Dudau <Liviu.Dudau@....com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        Brian Starkey <Brian.Starkey@....com>,
        "maarten.lankhorst@...ux.intel.com" 
        <maarten.lankhorst@...ux.intel.com>,
        "sean@...rly.run" <sean@...rly.run>,
        "imirkin@...m.mit.edu" <imirkin@...m.mit.edu>
CC:     "Jonathan Chai (Arm Technology China)" <Jonathan.Chai@....com>,
        "Julien Yin (Arm Technology China)" <Julien.Yin@....com>,
        "Thomas Sun (Arm Technology China)" <thomas.Sun@....com>,
        "Lowry Li (Arm Technology China)" <Lowry.Li@....com>,
        Ayan Halder <Ayan.Halder@....com>,
        "Tiannan Zhu (Arm Technology China)" <Tiannan.Zhu@....com>,
        "Yiqi Kang (Arm Technology China)" <Yiqi.Kang@....com>,
        nd <nd@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Ben Davis <Ben.Davis@....com>,
        "Oscar Zhang (Arm Technology China)" <Oscar.Zhang@....com>,
        "Channing Chen (Arm Technology China)" <Channing.Chen@....com>,
        Mihail Atanassov <Mihail.Atanassov@....com>,
        "james qian wang (Arm Technology China)" <james.qian.wang@....com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: [PATCH v6 1/4] drm: Add a new helper drm_color_ctm_s31_32_to_qm_n()

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) <james.qian.wang@....com>
Reviewed-by: Mihail Atanassov <mihail.atanassov@....com>
Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
---
 drivers/gpu/drm/drm_color_mgmt.c | 36 ++++++++++++++++++++++++++++++++
 include/drm/drm_color_mgmt.h     |  2 ++
 2 files changed, 38 insertions(+)

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,
--
2.20.1