Re: [PATCH] CorebootPayloadPkg: Use correct BytesPerScanLine

["You, Benjamin" <benjamin.you@intel.com>]

Hi Arthur,

Could you please give more details about your case that 
HorizontalResolution * (BitsPerPixel / 8) and pFbInfo->BytesPerScanLine 
don't match?

I did a brief search in Coreboot source and found following comments in 
coreboot-4.6\src\lib\edid.c:

  /* In the case of (e.g.) 24 framebuffer bits per pixel, the convention
   * nowadays seems to be to round it up to the nearest reasonable
   * boundary, because otherwise the byte-packing is hideous.
   
So it appears framebuffer BitsPerPixel will likely be 16 or 32, and the 
following statement in the same file calculates:

  edid->x_resolution = edid->bytes_per_line / (fb_bpp / 8);

which results in bytes_per_line (already rounded up to be 32 or 64 byte 
aligned) matching x_resolution * (fb_bpp / 8).

There are cases that even if panel bits_per_pixel is 24, the framebuffer 
bits_per_pixel is still 32, as shown in 
coreboot-4.6\src\drivers\emulation\qemu\bochs.c:

  edid.panel_bits_per_pixel = 24;
  edid_set_framebuffer_bits_per_pixel(&edid, 32, 0);

It would be good if you could help with more details on how the mismatch 
happened in your case as I may have missed something.

Thanks,

- ben

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> arthur@aheymans.xyz
> Sent: Wednesday, January 24, 2018 6:58 PM
> To: edk2-devel@lists.01.org
> Cc: Arthur Heymans <arthur@aheymans.xyz>
> Subject: [edk2] [PATCH] CorebootPayloadPkg: Use correct BytesPerScanLine
> 
> From: Arthur Heymans <arthur@aheymans.xyz>
> 
> Fetch BytesPerScanLine from coreboot table to reflect how the actual
> framebuffer is set up instead of guessing it from the horizontal
> resolution.
> 
> This fixes a garbled display when HorizontalResolution * (BitsPerPixel
> / 8) and pFbInfo->BytesPerScanLine don't match.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
> 
> diff --git a/CorebootPayloadPkg/FbGop/FbGop.c
> b/CorebootPayloadPkg/FbGop/FbGop.c
> index 37d6def7f7..6790617033 100644
> --- a/CorebootPayloadPkg/FbGop/FbGop.c
> +++ b/CorebootPayloadPkg/FbGop/FbGop.c
> @@ -822,7 +822,7 @@ FbGopCheckForVbe (
>    BitsPerPixel         = pFbInfo->BitsPerPixel;
>    HorizontalResolution = pFbInfo->HorizontalResolution;
>    VerticalResolution   = pFbInfo->VerticalResolution;
> -  BytesPerScanLine     = HorizontalResolution * (BitsPerPixel / 8);
> +  BytesPerScanLine     = pFbInfo->BytesPerScanLine;
> 
>    ModeBuffer = (FB_VIDEO_MODE_DATA *) AllocatePool (
> 
> 
> 				ModeNumber * sizeof
> (FB_VIDEO_MODE_DATA)
> --
> 2.16.1
> 
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel