[PATCH v5 2/6] drm/format-helper: Add drm_fb_xrgb8888_to_mono_reversed()

Javier Martinez Canillas
2022-02-11T14:34:18Z

Add support to convert from XR24 to reversed monochrome for drivers that
control monochromatic display panels, that only have 1 bit per pixel.

The function does a line-by-line conversion doing an intermediate step
first from XR24 to 8-bit grayscale and then to reversed monochrome.

The drm_fb_gray8_to_mono_reversed_line() helper was based on code from
drivers/gpu/drm/tiny/repaper.c driver.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
---

Changes in v5:
- Use drm_WARN_ON* macros instead of deprecated ones (Thomas Zimmermann)

Changes in v4:
- Rename end_offset to end_len (Thomas Zimmermann)
- Warn once if dst_pitch is not a multiple of 8 (Thomas Zimmermann)
- Drop drm_fb_gray8_to_mono_reversed() that's not used (Thomas Zimmermann)
- Allocate single buffer for both copy cma memory and gray8 (Thomas Zimmermann)
- Add Thomas Zimmermann Reviewed-by tag to patch adding XR24 -> mono helper.

Changes in v3:
- Also add a drm_fb_xrgb8888_to_mono_reversed() helper (Thomas Zimmermann)
- Split lines copy to drm_fb_gray8_to_mono_reversed_line() (Thomas Zimmermann)
- Handle case where the source buffer is not aligned to 8 (Thomas Zimmermann)

drivers/gpu/drm/drm_format_helper.c | 110 ++++++++++++++++++++++++++++
include/drm/drm_format_helper.h | 4 +
2 files changed, 114 insertions(+)

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index b981712623d3..bc0f49773868 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c
@@ -12,9 +12,11 @@
#include <linux/slab.h>
#include <linux/io.h>

+#include <drm/drm_device.h>
#include <drm/drm_format_helper.h>
#include <drm/drm_framebuffer.h>
#include <drm/drm_fourcc.h>
+#include <drm/drm_print.h>
#include <drm/drm_rect.h>

static unsigned int clip_offset(const struct drm_rect *clip, unsigned int pitch, unsigned int cpp)
@@ -591,3 +593,111 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
return -EINVAL;
}
EXPORT_SYMBOL(drm_fb_blit_toio);
+
+static void drm_fb_gray8_to_mono_reversed_line(u8 *dst, const u8 *src, unsigned int pixels,
+ unsigned int start_offset, unsigned int end_len)
+{
+ unsigned int xb, i;
+
+ for (xb = 0; xb < pixels; xb++) {
+ unsigned int start = 0, end = 8;
+ u8 byte = 0x00;
+
+ if (xb == 0 && start_offset)
+ start = start_offset;
+
+ if (xb == pixels - 1 && end_len)
+ end = end_len;
+
+ for (i = start; i < end; i++) {
+ unsigned int x = xb * 8 + i;
+
+ byte >>= 1;
+ if (src[x] >> 7)
+ byte |= BIT(7);
+ }
+ *dst++ = byte;
+ }
+}
+
+/**
+ * drm_fb_xrgb8888_to_mono_reversed - Convert XRGB8888 to reversed monochrome
+ * @dst: reversed monochrome destination buffer
+ * @dst_pitch: Number of bytes between two consecutive scanlines within dst
+ * @src: XRGB8888 source buffer
+ * @fb: DRM framebuffer
+ * @clip: Clip rectangle area to copy
+ *
+ * DRM doesn't have native monochrome support.
+ * Such drivers can announce the commonly supported XR24 format to userspace
+ * and use this function to convert to the native format.
+ *
+ * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
+ * then the result is converted from grayscale to reversed monohrome.
+ */
+void drm_fb_xrgb8888_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *vaddr,
+ const struct drm_framebuffer *fb, const struct drm_rect *clip)
+{
+ unsigned int linepixels = drm_rect_width(clip);
+ unsigned int lines = clip->y2 - clip->y1;
+ unsigned int cpp = fb->format->cpp[0];
+ unsigned int len_src32 = linepixels * cpp;
+ struct drm_device *dev = fb->dev;
+ unsigned int start_offset, end_len;
+ unsigned int y;
+ u8 *mono = dst, *gray8;
+ u32 *src32;
+
+ if (drm_WARN_ON(dev, fb->format->format != DRM_FORMAT_XRGB8888))
+ return;
+
+ /*
+ * The reversed mono destination buffer contains 1 bit per pixel
+ * and destination scanlines have to be in multiple of 8 pixels.
+ */
+ if (!dst_pitch)
+ dst_pitch = DIV_ROUND_UP(linepixels, 8);
+
+ drm_WARN_ONCE(dev, dst_pitch % 8 != 0, "dst_pitch is not a multiple of 8\n");
+
+ /*
+ * The cma memory is write-combined so reads are uncached.
+ * Speed up by fetching one line at a time.
+ *
+ * Also, format conversion from XR24 to reversed monochrome
+ * 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 = kmalloc(len_src32 + linepixels, GFP_KERNEL);
+ if (!src32)
+ return;
+
+ gray8 = (u8 *)src32 + len_src32;
+
+ /*
+ * For damage handling, it is possible that only parts of the source
+ * buffer is copied and this could lead to start and end pixels that
+ * are not aligned to multiple of 8.
+ *
+ * Calculate if the start and end pixels are not aligned and set the
+ * offsets for the reversed mono line conversion function to adjust.
+ */
+ start_offset = clip->x1 % 8;
+ end_len = clip->x2 % 8;
+
+ 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_mono_reversed_line(mono, gray8, dst_pitch,
+ start_offset, end_len);
+ vaddr += fb->pitches[0];
+ mono += dst_pitch;
+ }
+
+ kfree(src32);
+}
+EXPORT_SYMBOL(drm_fb_xrgb8888_to_mono_reversed);
diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
index b30ed5de0a33..0b0937c0b2f6 100644
--- a/include/drm/drm_format_helper.h
+++ b/include/drm/drm_format_helper.h
@@ -43,4 +43,8 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
const void *vmap, const struct drm_framebuffer *fb,
const struct drm_rect *rect);

+void drm_fb_xrgb8888_to_mono_reversed(void *dst, unsigned int dst_pitch, const void *src,
+ const struct drm_framebuffer *fb,
+ const struct drm_rect *clip);
+
#endif /* __LINUX_DRM_FORMAT_HELPER_H */
--
2.34.1