On 07/11, Daniel Vetter wrote:
> On Tue, Jun 25, 2019 at 10:38:31PM -0300, Rodrigo Siqueira wrote:
> > The compute_crc() function is responsible for calculating the
> > framebuffer CRC value; due to the XRGB format, this function has to
> > ignore the alpha channel during the CRC computation. Therefore,
> > compute_crc() set zero to the alpha channel directly in the input
> > framebuffer, which is not a problem since this function receives a copy
> > of the original buffer. However, if we want to use this function in a
> > context without a buffer copy, it will change the initial value. This
> > patch makes compute_crc() calculate the CRC value without modifying the
> > input framebuffer.
>
> Uh why? For writeback we're writing the output too, so we can write
> whatever we want to into the alpha channel. For writeback we should never
> accept a pixel format where alpha actually matters, that doesn't make
> sense. You can't see through a real screen either, they are all opaque :-)
> -Daniel
Hmmm,
I see your point and I agree, but even though we can write whatever we
want in the output, don’t you think that is weird to change the
framebuffer value in the compute_crc() function?
Thanks
> >
> > Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/vkms/vkms_composer.c | 31 +++++++++++++++++-----------
> > 1 file changed, 19 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> > index 51a270514219..8126aa0f968f 100644
> > --- a/drivers/gpu/drm/vkms/vkms_composer.c
> > +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> > @@ -6,33 +6,40 @@
> > #include <drm/drm_atomic_helper.h>
> > #include <drm/drm_gem_framebuffer_helper.h>
> >
> > +static u32 get_pixel_from_buffer(int x, int y, const u8 *buffer,
> > + const struct vkms_composer *composer)
> > +{
> > + int src_offset = composer->offset + (y * composer->pitch)
> > + + (x * composer->cpp);
> > +
> > + return *(u32 *)&buffer[src_offset];
> > +}
> > +
> > /**
> > * compute_crc - Compute CRC value on output frame
> > *
> > - * @vaddr_out: address to final framebuffer
> > + * @vaddr: address to final framebuffer
> > * @composer: framebuffer's metadata
> > *
> > * returns CRC value computed using crc32 on the visible portion of
> > * the final framebuffer at vaddr_out
> > */
> > -static uint32_t compute_crc(void *vaddr_out, struct vkms_composer *composer)
> > +static uint32_t compute_crc(const u8 *vaddr,
> > + const struct vkms_composer *composer)
> > {
> > - int i, j, src_offset;
> > + int x, y;
> > int x_src = composer->src.x1 >> 16;
> > int y_src = composer->src.y1 >> 16;
> > int h_src = drm_rect_height(&composer->src) >> 16;
> > int w_src = drm_rect_width(&composer->src) >> 16;
> > - u32 crc = 0;
> > + u32 crc = 0, pixel = 0;
> >
> > - for (i = y_src; i < y_src + h_src; ++i) {
> > - for (j = x_src; j < x_src + w_src; ++j) {
> > - src_offset = composer->offset
> > - + (i * composer->pitch)
> > - + (j * composer->cpp);
> > + for (y = y_src; y < y_src + h_src; ++y) {
> > + for (x = x_src; x < x_src + w_src; ++x) {
> > /* XRGB format ignores Alpha channel */
> > - memset(vaddr_out + src_offset + 24, 0, 8);
> > - crc = crc32_le(crc, vaddr_out + src_offset,
> > - sizeof(u32));
> > + pixel = get_pixel_from_buffer(x, y, vaddr, composer);
> > + bitmap_clear((void *)&pixel, 0, 8);
> > + crc = crc32_le(crc, (void *)&pixel, sizeof(u32));
> > }
> > }
> >
> > --
> > 2.21.0
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
--
Rodrigo Siqueira
https://siqueira.tech
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