On Wed, Jun 17, 2015 at 1:05 PM, Michael Büsch m@bues.ch wrote:

The expression (~0 >> x) will always yield all-ones, because the right shift is an arithmetic right shift that will always shift ones in. Accordingly ~(~0 >> x) will always be zero. Hence 'mask' will always be zero in this case.

Fix this by forcing a logical right shift instead of an arithmetic right shift by using an unsigned int constant.

Signed-off-by: Michael Buesch m@bues.ch

Confirmed that this does indeed happen with

#include <stdio.h> int main(int argc, char *argv[]) { unsigned mask = ~(~0 >> (32 - (argv[1][0] - '0'))); printf("%08x\n", mask); }

I guess fbdev/nvidia/nv_accel.c was the source of all this, as the code is identical, and it probably came first.

FWIW this is

Reviewed-by: Ilia Mirkin imirkin@alum.mit.edu

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This patch is untested, because I do not have the hardware.

Index: linux/drivers/gpu/drm/nouveau/nv50_fbcon.c

--- linux.orig/drivers/gpu/drm/nouveau/nv50_fbcon.c +++ linux/drivers/gpu/drm/nouveau/nv50_fbcon.c @@ -96,7 +96,7 @@ nv50_fbcon_imageblit(struct fb_info *inf struct nouveau_drm *drm = nouveau_drm(nfbdev->dev); struct nouveau_channel *chan = drm->channel; uint32_t width, dwords, *data = (uint32_t *)image->data;

•   uint32_t mask = ~(~0 >> (32 - info->var.bits_per_pixel));
  

•   uint32_t mask = ~(~0U >> (32 - info->var.bits_per_pixel));
    uint32_t *palette = info->pseudo_palette;
    int ret;
  
  

Index: linux/drivers/gpu/drm/nouveau/nvc0_fbcon.c

--- linux.orig/drivers/gpu/drm/nouveau/nvc0_fbcon.c +++ linux/drivers/gpu/drm/nouveau/nvc0_fbcon.c @@ -96,7 +96,7 @@ nvc0_fbcon_imageblit(struct fb_info *inf struct nouveau_drm *drm = nouveau_drm(nfbdev->dev); struct nouveau_channel *chan = drm->channel; uint32_t width, dwords, *data = (uint32_t *)image->data;

•   uint32_t mask = ~(~0 >> (32 - info->var.bits_per_pixel));
  

•   uint32_t mask = ~(~0U >> (32 - info->var.bits_per_pixel));
    uint32_t *palette = info->pseudo_palette;
    int ret;
  
  

Index: linux/drivers/video/fbdev/nvidia/nv_accel.c

--- linux.orig/drivers/video/fbdev/nvidia/nv_accel.c +++ linux/drivers/video/fbdev/nvidia/nv_accel.c @@ -351,7 +351,7 @@ static void nvidiafb_mono_color_expand(s const struct fb_image *image) { struct nvidia_par *par = info->par;

•   u32 fg, bg, mask = ~(~0 >> (32 - info->var.bits_per_pixel));
  

•   u32 fg, bg, mask = ~(~0U >> (32 - info->var.bits_per_pixel));
    u32 dsize, width, *data = (u32 *) image->data, tmp;
    int j, k = 0;
  
  
  

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