Re: [PATCH RFC 2/3] xen/arm: efi: Introduce and fill the vga_console_info

[Jan Beulich <jbeulich@suse.com>]

On 06.02.2022 20:28, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
> 
> In a follow-up patch will we want to add support for EFI framebuffer
> in dom0. Yet, Xen may not use the framebuffer, so it would be ideal
> to not have to enable CONFIG_VIDEO/CONFIG_VGA.
> 
> Introduce vga_console_info in a hacky way and move the code
> to fill it up from x86 to common.
> 
> Signed-off-by: Julien Grall <jgrall@amazon.com>
> 
> ----
> 
> This is a bit of a hack. Sent early to gather opinion on whether
> we should enable allow Dom0 to use the EFI Framebuffer even
> if Xen is built with CONFIG_VIDEO=n on Arm.

I have no input here; this will need to be settled among you Arm folks.
I have no objection to the code movement, just one nit:

> @@ -1025,6 +1026,77 @@ static void __init efi_get_apple_properties(void)
>      }
>  }
>  
> +static void __init efi_video_init(EFI_GRAPHICS_OUTPUT_PROTOCOL *gop,
> +                                  UINTN info_size,
> +                                  EFI_GRAPHICS_OUTPUT_MODE_INFORMATION *mode_info)
> +{
> +#if defined(CONFIG_VIDEO) || defined(CONFIG_ARM)
> +    int bpp = 0;
> +
> +    switch ( mode_info->PixelFormat )
> +    {
> +    case PixelRedGreenBlueReserved8BitPerColor:
> +        vga_console_info.u.vesa_lfb.red_pos = 0;
> +        vga_console_info.u.vesa_lfb.red_size = 8;
> +        vga_console_info.u.vesa_lfb.green_pos = 8;
> +        vga_console_info.u.vesa_lfb.green_size = 8;
> +        vga_console_info.u.vesa_lfb.blue_pos = 16;
> +        vga_console_info.u.vesa_lfb.blue_size = 8;
> +        vga_console_info.u.vesa_lfb.rsvd_pos = 24;
> +        vga_console_info.u.vesa_lfb.rsvd_size = 8;
> +        bpp = 32;
> +        break;
> +    case PixelBlueGreenRedReserved8BitPerColor:
> +        vga_console_info.u.vesa_lfb.red_pos = 16;
> +        vga_console_info.u.vesa_lfb.red_size = 8;
> +        vga_console_info.u.vesa_lfb.green_pos = 8;
> +        vga_console_info.u.vesa_lfb.green_size = 8;
> +        vga_console_info.u.vesa_lfb.blue_pos = 0;
> +        vga_console_info.u.vesa_lfb.blue_size = 8;
> +        vga_console_info.u.vesa_lfb.rsvd_pos = 24;
> +        vga_console_info.u.vesa_lfb.rsvd_size = 8;
> +        bpp = 32;
> +        break;
> +    case PixelBitMask:
> +        bpp = set_color(mode_info->PixelInformation.RedMask, bpp,
> +                        &vga_console_info.u.vesa_lfb.red_pos,
> +                        &vga_console_info.u.vesa_lfb.red_size);
> +        bpp = set_color(mode_info->PixelInformation.GreenMask, bpp,
> +                        &vga_console_info.u.vesa_lfb.green_pos,
> +                        &vga_console_info.u.vesa_lfb.green_size);
> +        bpp = set_color(mode_info->PixelInformation.BlueMask, bpp,
> +                        &vga_console_info.u.vesa_lfb.blue_pos,
> +                        &vga_console_info.u.vesa_lfb.blue_size);
> +        if ( mode_info->PixelInformation.ReservedMask )
> +            bpp = set_color(mode_info->PixelInformation.ReservedMask, bpp,
> +                            &vga_console_info.u.vesa_lfb.rsvd_pos,
> +                            &vga_console_info.u.vesa_lfb.rsvd_size);
> +        if ( bpp > 0 )
> +            break;
> +        /* fall through */
> +    default:
> +        PrintErr(L"Current graphics mode is unsupported!\r\n");
> +        bpp  = 0;
> +        break;
> +    }
> +    if ( bpp > 0 )
> +    {
> +        vga_console_info.video_type = XEN_VGATYPE_EFI_LFB;
> +        vga_console_info.u.vesa_lfb.gbl_caps = 2; /* possibly non-VGA */
> +        vga_console_info.u.vesa_lfb.width =
> +            mode_info->HorizontalResolution;
> +        vga_console_info.u.vesa_lfb.height = mode_info->VerticalResolution;
> +        vga_console_info.u.vesa_lfb.bits_per_pixel = bpp;
> +        vga_console_info.u.vesa_lfb.bytes_per_line =
> +            (mode_info->PixelsPerScanLine * bpp + 7) >> 3;
> +        vga_console_info.u.vesa_lfb.lfb_base = gop->Mode->FrameBufferBase;
> +        vga_console_info.u.vesa_lfb.ext_lfb_base = gop->Mode->FrameBufferBase >> 32;
> +        vga_console_info.u.vesa_lfb.lfb_size =
> +            (gop->Mode->FrameBufferSize + 0xffff) >> 16;
> +    }
> +#endif
> +}

While you move this code, could you please insert blank lines between
non-fall-through case blocks, and perhaps another one between the switch()
and the if() blocks? And it looks like
- the "gop" parameter could also do with becoming pointer-to-const,
- the expanded #ifdef could do with a comment briefly explaining why Arm
  needs-special casing.

Jan