Re: [PATCH 2/3] mach64: fix image corruption due to reading accelerator registers

["Ville Syrjälä" <syrjala@sci.fi>]

On Sat, Aug 25, 2018 at 03:51:52PM -0400, Mikulas Patocka wrote:
> Reading the registers without waiting for engine idle returns
> unpredictable values. These unpredictable values result in display
> corruption - if atyfb_imageblit reads the content of DP_PIX_WIDTH with the
> bit DP_HOST_TRIPLE_EN set (from previous invocation), the driver would
> never ever clear the bit, resulting in display corruption.
> 
> We don't want to wait for idle because it would degrade performance, so
> this patch modifies the driver so that it never reads accelerator
> registers.
> 
> HOST_CNTL doesn't have to be read, we can just write it with
> HOST_BYTE_ALIGN because no other part of the driver cares if
> HOST_BYTE_ALIGN is set.
> 
> DP_PIX_WIDTH is written in the functions atyfb_copyarea and atyfb_fillrect
> with the default value and in atyfb_imageblit with the value set according
> to the source image data.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: stable@vger.kernel.org
> 
> ---
>  drivers/video/fbdev/aty/mach64_accel.c |   22 +++++++++-------------
>  1 file changed, 9 insertions(+), 13 deletions(-)
> 
> Index: linux-stable/drivers/video/fbdev/aty/mach64_accel.c
> =================================> --- linux-stable.orig/drivers/video/fbdev/aty/mach64_accel.c	2018-08-24 19:51:34.000000000 +0200
> +++ linux-stable/drivers/video/fbdev/aty/mach64_accel.c	2018-08-24 20:28:55.000000000 +0200
> @@ -127,7 +127,7 @@ void aty_init_engine(struct atyfb_par *p
>  
>  	/* set host attributes */
>  	wait_for_fifo(13, par);
> -	aty_st_le32(HOST_CNTL, 0, par);
> +	aty_st_le32(HOST_CNTL, HOST_BYTE_ALIGN, par);
>  
>  	/* set pattern attributes */
>  	aty_st_le32(PAT_REG0, 0, par);
> @@ -233,7 +233,8 @@ void atyfb_copyarea(struct fb_info *info
>  		rotation = rotation24bpp(dx, direction);
>  	}
>  
> -	wait_for_fifo(4, par);
> +	wait_for_fifo(5, par);
> +	aty_st_le32(DP_PIX_WIDTH, par->crtc.dp_pix_width, par);
>  	aty_st_le32(DP_SRC, FRGD_SRC_BLIT, par);
>  	aty_st_le32(SRC_Y_X, (sx << 16) | sy, par);
>  	aty_st_le32(SRC_HEIGHT1_WIDTH1, (width << 16) | area->height, par);
> @@ -269,7 +270,8 @@ void atyfb_fillrect(struct fb_info *info
>  		rotation = rotation24bpp(dx, DST_X_LEFT_TO_RIGHT);
>  	}
>  
> -	wait_for_fifo(3, par);
> +	wait_for_fifo(4, par);
> +	aty_st_le32(DP_PIX_WIDTH, par->crtc.dp_pix_width, par);
>  	aty_st_le32(DP_FRGD_CLR, color, par);
>  	aty_st_le32(DP_SRC,
>  		    BKGD_SRC_BKGD_CLR | FRGD_SRC_FRGD_CLR | MONO_SRC_ONE,
> @@ -284,7 +286,7 @@ void atyfb_imageblit(struct fb_info *inf
>  {
>  	struct atyfb_par *par = (struct atyfb_par *) info->par;
>  	u32 src_bytes, dx = image->dx, dy = image->dy, width = image->width;
> -	u32 pix_width_save, pix_width, host_cntl, rotation = 0, src, mix;
> +	u32 pix_width, rotation = 0, src, mix;
>  
>  	if (par->asleep)
>  		return;
> @@ -296,8 +298,7 @@ void atyfb_imageblit(struct fb_info *inf
>  		return;
>  	}
>  
> -	pix_width = pix_width_save = aty_ld_le32(DP_PIX_WIDTH, par);
> -	host_cntl = aty_ld_le32(HOST_CNTL, par) | HOST_BYTE_ALIGN;
> +	pix_width = par->crtc.dp_pix_width;
>  
>  	switch (image->depth) {
>  	case 1:
> @@ -370,12 +371,11 @@ void atyfb_imageblit(struct fb_info *inf
>  		mix = FRGD_MIX_D_XOR_S | BKGD_MIX_D;
>  	}
>  
> -	wait_for_fifo(6, par);
> -	aty_st_le32(DP_WRITE_MASK, 0xFFFFFFFF, par);

Looks like init_engine() sets this one for us. So dropping should be ok.

> +	wait_for_fifo(5, par);
>  	aty_st_le32(DP_PIX_WIDTH, pix_width, par);
>  	aty_st_le32(DP_MIX, mix, par);
>  	aty_st_le32(DP_SRC, src, par);
> -	aty_st_le32(HOST_CNTL, host_cntl, par);
> +	aty_st_le32(HOST_CNTL, HOST_BYTE_ALIGN, par);

Presumably we could drop this as well since it never changes.

Either way
Reviewed-by: Ville Syrjälä <syrjala@sci.fi>

>  	aty_st_le32(DST_CNTL, DST_Y_TOP_TO_BOTTOM | DST_X_LEFT_TO_RIGHT | rotation, par);
>  
>  	draw_rect(dx, dy, width, image->height, par);
> @@ -424,8 +424,4 @@ void atyfb_imageblit(struct fb_info *inf
>  			aty_st_le32(HOST_DATA0, get_unaligned_le32(pbitmap), par);
>  		}
>  	}
> -
> -	/* restore pix_width */
> -	wait_for_fifo(1, par);
> -	aty_st_le32(DP_PIX_WIDTH, pix_width_save, par);
>  }

-- 
Ville Syrjälä
syrjala@sci.fi
http://www.sci.fi/~syrjala/