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Message-Id: <20250721-st7571-format-v2-5-159f4134098c@gmail.com>
Date: Mon, 21 Jul 2025 12:43:35 +0200
From: Marcus Folkesson <marcus.folkesson@...il.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>,
Javier Martinez Canillas <javierm@...hat.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org, Marcus Folkesson <marcus.folkesson@...il.com>
Subject: [PATCH v2 5/6] drm/format-helper: introduce
drm_fb_xrgb8888_to_gray2()
Convert XRGB8888 to 2bit grayscale.
It uses drm_fb_xrgb8888_to_gray8() to convert the pixels to gray8 as an
intermediate step before converting to gray2.
Signed-off-by: Marcus Folkesson <marcus.folkesson@...il.com>
---
drivers/gpu/drm/drm_format_helper.c | 108 ++++++++++++++++++++++++++++++++++++
include/drm/drm_format_helper.h | 4 ++
2 files changed, 112 insertions(+)
diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index 8f3daf38ca639d3d39742c2c9fa0c54a3a9297a5..bfeaa4db6929859ea029192a868e6d42741b31f2 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c
@@ -1253,6 +1253,25 @@ int drm_fb_blit(struct iosys_map *dst, const unsigned int *dst_pitch, uint32_t d
}
EXPORT_SYMBOL(drm_fb_blit);
+static void drm_fb_gray8_to_gray2_line(void *dbuf, const void *sbuf, unsigned int pixels)
+{
+ u8 *dbuf8 = dbuf;
+ const u8 *sbuf8 = sbuf;
+ u8 px;
+
+ while (pixels) {
+ unsigned int i, bits = min(pixels, 4U);
+ u8 byte = 0;
+
+ for (i = 0; i < bits; i++, pixels--) {
+ byte >>= 2;
+ px = (*sbuf8++ * 3 + 127) / 255;
+ byte |= (px &= 0x03) << 6;
+ }
+ *dbuf8++ = byte;
+ }
+}
+
static void drm_fb_gray8_to_mono_line(void *dbuf, const void *sbuf, unsigned int pixels)
{
u8 *dbuf8 = dbuf;
@@ -1359,3 +1378,92 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
}
}
EXPORT_SYMBOL(drm_fb_xrgb8888_to_mono);
+
+/**
+ * drm_fb_xrgb8888_to_gray2 - Convert XRGB8888 to gray2
+ * @dst: Array of gray2 destination buffer
+ * @dst_pitch: Array of numbers of bytes between the start of two consecutive scanlines
+ * within @dst; can be NULL if scanlines are stored next to each other.
+ * @src: Array of XRGB8888 source buffers
+ * @fb: DRM framebuffer
+ * @clip: Clip rectangle area to copy
+ * @state: Transform and conversion state
+ *
+ * This function copies parts of a framebuffer to display memory and converts the
+ * color format during the process. Destination and framebuffer formats must match. The
+ * parameters @dst, @dst_pitch and @src refer to arrays. Each array must have at
+ * least as many entries as there are planes in @fb's format. Each entry stores the
+ * value for the format's respective color plane at the same index.
+ *
+ * This function does not apply clipping on @dst (i.e. the destination is at the
+ * top-left corner). The first pixel (upper left corner of the clip rectangle) will
+ * be converted and copied to the two first bits (LSB) in the first byte of the gray2
+ * destination buffer. If the caller requires that the first pixel in a byte must
+ * be located at an x-coordinate that is a multiple of 8, then the caller must take
+ * care itself of supplying a suitable clip rectangle.
+ *
+ * DRM doesn't have native gray2 support. Drivers can use this function for
+ * gray2 devices that don't support XRGB8888 natively. Such drivers can
+ * announce the commonly supported XR24 format to userspace and use this function
+ * to convert to the native format.
+ *
+ */
+void drm_fb_xrgb8888_to_gray2(struct iosys_map *dst, const unsigned int *dst_pitch,
+ const struct iosys_map *src, const struct drm_framebuffer *fb,
+ const struct drm_rect *clip, struct drm_format_conv_state *state)
+{
+ static const unsigned int default_dst_pitch[DRM_FORMAT_MAX_PLANES] = {
+ 0, 0, 0, 0
+ };
+ unsigned int linepixels = drm_rect_width(clip);
+ unsigned int lines = drm_rect_height(clip);
+ unsigned int cpp = fb->format->cpp[0];
+ unsigned int len_src32 = linepixels * cpp;
+ struct drm_device *dev = fb->dev;
+ void *vaddr = src[0].vaddr;
+ unsigned int dst_pitch_0;
+ unsigned int y;
+ u8 *gray2 = dst[0].vaddr, *gray8;
+ u32 *src32;
+
+ if (drm_WARN_ON(dev, fb->format->format != DRM_FORMAT_XRGB8888))
+ return;
+
+ if (!dst_pitch)
+ dst_pitch = default_dst_pitch;
+ dst_pitch_0 = dst_pitch[0];
+
+ /*
+ * The gray2 destination buffer contains 2 bit per pixel
+ */
+ if (!dst_pitch_0)
+ dst_pitch_0 = DIV_ROUND_UP(linepixels, 4);
+
+ /*
+ * The dma memory is write-combined so reads are uncached.
+ * Speed up by fetching one line at a time.
+ *
+ * Also, format conversion from XR24 to gray2 are done
+ * line-by-line but are converted to 8-bit grayscale as an
+ * intermediate step.
+ *
+ * Allocate a buffer to be used for both copying from the cma
+ * memory and to store the intermediate grayscale line pixels.
+ */
+ src32 = drm_format_conv_state_reserve(state, len_src32 + linepixels, GFP_KERNEL);
+ if (!src32)
+ return;
+
+ gray8 = (u8 *)src32 + len_src32;
+
+ vaddr += clip_offset(clip, fb->pitches[0], cpp);
+ for (y = 0; y < lines; y++) {
+ src32 = memcpy(src32, vaddr, len_src32);
+ drm_fb_xrgb8888_to_gray8_line(gray8, src32, linepixels);
+ drm_fb_gray8_to_gray2_line(gray2, gray8, linepixels);
+ vaddr += fb->pitches[0];
+ gray2 += dst_pitch_0;
+ }
+}
+EXPORT_SYMBOL(drm_fb_xrgb8888_to_gray2);
+
diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
index 562bc383ece4e90d96aa92b47b4f69609f825a6e..8488befafb7e0e0311f87bd2fef5011bab45065b 100644
--- a/include/drm/drm_format_helper.h
+++ b/include/drm/drm_format_helper.h
@@ -136,4 +136,8 @@ void drm_fb_xrgb8888_to_mono(struct iosys_map *dst, const unsigned int *dst_pitc
const struct iosys_map *src, const struct drm_framebuffer *fb,
const struct drm_rect *clip, struct drm_format_conv_state *state);
+void drm_fb_xrgb8888_to_gray2(struct iosys_map *dst, const unsigned int *dst_pitch,
+ const struct iosys_map *src, const struct drm_framebuffer *fb,
+ const struct drm_rect *clip, struct drm_format_conv_state *state);
+
#endif /* __LINUX_DRM_FORMAT_HELPER_H */
--
2.49.0
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