[PATCH 2/2] efi: earlycon: Add support for generic framebuffers and move to fbdev subsystem

[Andy Shevchenko]

On Thu, Jul 28, 2022 at 4:32 PM Markuss Broks <markuss.broks at gmail.com> wrote:
>
> Add early console support for generic linear framebuffer devices.
> This driver supports probing from cmdline early parameters
> or from the device-tree using information in simple-framebuffer node.
> The EFI functionality should be retained in whole.
> The driver was disabled on ARM because of a bug in early_ioremap
> implementation on ARM.

...

> -               efifb,[options]
> +               efifb
>                         Start an early, unaccelerated console on the EFI
> -                       memory mapped framebuffer (if available). On cache
> -                       coherent non-x86 systems that use system memory for
> -                       the framebuffer, pass the 'ram' option so that it is
> -                       mapped with the correct attributes.
> +                       memory mapped framebuffer (if available).

If somebody passes those (legacy) options, what will happen?

...

>  config EFI_EARLYCON
> -       def_bool y
> -       depends on SERIAL_EARLYCON && !ARM && !IA64
> -       select FONT_SUPPORT
> -       select ARCH_USE_MEMREMAP_PROT
> +       bool "EFI early console support"
> +       depends on FB_EARLYCON && !IA64

This doesn't sound right. Previously on my configuration it was
selected automatically, now I need to select it explicitly? I mean
that for me EFI_EARLYCON should be selected by default as it was
before.

...

> +static int __init simplefb_earlycon_remap_fb(void)
> +{
> +       int is_ram;

+ blank line.

> +       /* bail if there is no bootconsole or it has been disabled already */
> +       if (!earlycon_console || !(earlycon_console->flags & CON_ENABLED))
> +               return 0;
> +
> +       is_ram = region_intersects(info.phys_base, info.size,
> +                                  IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE);
> +       is_ram = is_ram == REGION_INTERSECTS;

Was it in the original code? Otherwise, I would go with plain conditional:

  if (region_intersects())
    base = ...
  else
    base = ...

> +       info.virt_base = memremap(info.phys_base, info.size,
> +                                 is_ram ? MEMREMAP_WB : MEMREMAP_WC);
> +
> +       return info.virt_base ? 0 : -ENOMEM;
> +}

...

> +static void simplefb_earlycon_write_char(u8 *dst, unsigned char c, unsigned int h)
> +{
> +       const u8 *src;
> +       int m, n, bytes;
> +       u8 x;
> +
> +       bytes = BITS_TO_BYTES(font->width);
> +       src = font->data + c * font->height * bytes + h * bytes;
> +
> +       for (m = 0; m < font->width; m++) {
> +               n = m % 8;
> +               x = *(src + m / 8);
> +               if ((x >> (7 - n)) & 1)
> +                       memset(dst, 0xff, (info.depth / 8));
> +               else
> +                       memset(dst, 0, (info.depth / 8));
> +               dst += (info.depth / 8);
> +       }
> +}

Wondering if we already have something like this in DRM/fbdev and can
split into a generic helper.

...

> +       ret = sscanf(device->options, "%u,%u,%u", &info.x, &info.y, &info.depth);
> +       if (ret != 3)
> +               return -ENODEV;

Don't we have some standard template of this, something like XxYxD,
where X, Y, and D are respective decimal numbers?

-- 
With Best Regards,
Andy Shevchenko