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    Subject[PATCH 5.18 263/879] drm/format-helper: Fix XRGB888 to monochrome conversion
    Date
    From: Geert Uytterhoeven <geert@linux-m68k.org>

    [ Upstream commit 7392f2459eefcdab1d998af002d2b8b16fe4a2fd ]

    The conversion functions drm_fb_xrgb8888_to_mono() and
    drm_fb_gray8_to_mono_line() do not behave correctly when the
    horizontal boundaries of the clip rectangle are not multiples of 8:
    a. When x1 % 8 != 0, the calculated pitch is not correct,
    b. When x2 % 8 != 0, the pixel data for the last byte is wrong.

    Simplify the code and fix (a) by:
    1. Removing start_offset, and always storing the first pixel in the
    first bit of the monochrome destination buffer.
    Drivers that require the first pixel in a byte to be located at an
    x-coordinate that is a multiple of 8 can always align the clip
    rectangle before calling drm_fb_xrgb8888_to_mono().
    Note that:
    - The ssd130x driver does not need the alignment, as the
    monochrome buffer is a temporary format,
    - The repaper driver always updates the full screen, so the clip
    rectangle is always aligned.
    2. Passing the number of pixels to drm_fb_gray8_to_mono_line(),
    instead of the number of bytes, and the number of pixels in the
    last byte.

    Fix (b) by explicitly setting the target bit, instead of always setting
    bit 7 and shifting the value in each loop iteration.

    Remove the bogus pitch check, which operates on bytes instead of pixels,
    and triggers when e.g. flashing the cursor on a text console with a font
    that is 8 pixels wide.

    Drop the confusing comment about scanlines, as a pitch in bytes always
    contains a multiple of 8 pixels.

    While at it, use the drm_rect_height() helper instead of open-coding the
    same operation.

    Update the comments accordingly.

    Fixes: bcf8b616deb87941 ("drm/format-helper: Add drm_fb_xrgb8888_to_mono_reversed()")
    Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
    Acked-by: Javier Martinez Canillas <javierm@redhat.com>
    Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20220317081830.1211400-3-geert@linux-m68k.org
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/gpu/drm/drm_format_helper.c | 55 ++++++++++-------------------
    1 file changed, 18 insertions(+), 37 deletions(-)

    diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
    index 5d9d0c695845..e085f855a199 100644
    --- a/drivers/gpu/drm/drm_format_helper.c
    +++ b/drivers/gpu/drm/drm_format_helper.c
    @@ -594,27 +594,16 @@ int drm_fb_blit_toio(void __iomem *dst, unsigned int dst_pitch, uint32_t dst_for
    }
    EXPORT_SYMBOL(drm_fb_blit_toio);

    -static void drm_fb_gray8_to_mono_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;
    +static void drm_fb_gray8_to_mono_line(u8 *dst, const u8 *src, unsigned int pixels)
    +{
    + while (pixels) {
    + unsigned int i, bits = min(pixels, 8U);
    + u8 byte = 0;

    - byte >>= 1;
    - if (src[x] >> 7)
    - byte |= BIT(7);
    + for (i = 0; i < bits; i++, pixels--) {
    + if (*src++ >= 128)
    + byte |= BIT(i);
    }
    *dst++ = byte;
    }
    @@ -634,16 +623,22 @@ static void drm_fb_gray8_to_mono_line(u8 *dst, const u8 *src, unsigned int pixel
    *
    * This function uses drm_fb_xrgb8888_to_gray8() to convert to grayscale and
    * then the result is converted from grayscale to monochrome.
    + *
    + * The first pixel (upper left corner of the clip rectangle) will be converted
    + * and copied to the first bit (LSB) in the first byte of the monochrome
    + * 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.
    */
    void drm_fb_xrgb8888_to_mono(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 lines = drm_rect_height(clip);
    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;
    @@ -652,14 +647,11 @@ void drm_fb_xrgb8888_to_mono(void *dst, unsigned int dst_pitch, const void *vadd
    return;

    /*
    - * The mono destination buffer contains 1 bit per pixel and
    - * destination scanlines have to be in multiple of 8 pixels.
    + * The mono destination buffer contains 1 bit per pixel
    */
    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.
    @@ -677,22 +669,11 @@ void drm_fb_xrgb8888_to_mono(void *dst, unsigned int dst_pitch, const void *vadd

    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 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_line(mono, gray8, dst_pitch, start_offset, end_len);
    + drm_fb_gray8_to_mono_line(mono, gray8, linepixels);
    vaddr += fb->pitches[0];
    mono += dst_pitch;
    }
    --
    2.35.1


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