drm/format-helper: Add drm_fb_xrgb8888_to_mono_reversed()

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>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220214133710.3278506-3-javierm@redhat.com

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index b981712..bc0f497 100644 (file)
--- 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 b30ed5d..0b0937c 100644 (file)
--- 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 */