On Fri, Feb 11, 2022 at 10:19:23AM +0100, Javier Martinez Canillas wrote:
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.
...
+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;
This is invariant to the loop, can be moved out.
+ if (xb == pixels - 1 && end_len)
+ end = end_len;
Ditto. However it may require to factor out the following loop to a helper.
+ for (i = start; i < end; i++) {
+ unsigned int x = xb * 8 + i;
+
+ byte >>= 1;
+ if (src[x] >> 7)
+ byte |= BIT(7);
+ }
+ *dst++ = byte;
+ }
+}
...
+ /*
+ * 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);
round_up() ?
+ WARN_ONCE(dst_pitch % 8 != 0, "dst_pitch is not a multiple of 8\n");
I would move this to the if conditional, i.e.
if (dst_pitch)
WARN_ONCE(dst_pitch % 8 != 0, "dst_pitch is not a multiple of 8\n");
else
dst_pitch = round_up(linepixels, 8);
+ /*
+ * The cma memory is write-combined so reads are uncached.
CMA
+ * 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);
size_add() ?
+ if (!src32)
+ return;
...
+ /*
+ * 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;
ALIGN() ?
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