On Thu, 5 Dec 2019 at 16:42, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
>
> When commit 69c1f396f25b
>
> "efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation"
>
> moved the x86 specific EFI earlyprintk implementation to a shared location,
> it also tweaked the behaviour. In particular, it dropped a trick with full
> framebuffer remapping after page initialization, leading to two regressions:
> 1) very slow scrolling after page initialization,
> 2) kernel hang when the 'keep_bootcon' command line argument is passed.
>
> Putting the tweak back fixes #2 and mitigates #1, i.e., it limits the slow
> behavior to the early boot stages, presumably due to eliminating heavy
> map()/unmap() operations per each pixel line on the screen.
>
> Fixes: 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> [ardb: ensure efifb is unmapped again unless keep_bootcon is in effect]
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
> drivers/firmware/efi/earlycon.c | 40 +++++++++++++++++++++++++++++++++
> 1 file changed, 40 insertions(+)
>
> diff --git a/drivers/firmware/efi/earlycon.c b/drivers/firmware/efi/earlycon.c
> index c9a0efca17b0..0bc4fe741415 100644
> --- a/drivers/firmware/efi/earlycon.c
> +++ b/drivers/firmware/efi/earlycon.c
> @@ -13,18 +13,57 @@
>
> #include <asm/early_ioremap.h>
>
> +static const struct console *earlycon_console __initdata;
> static const struct font_desc *font;
> static u32 efi_x, efi_y;
> static u64 fb_base;
> static pgprot_t fb_prot;
> +static void *efi_fb;
> +
> +/*
> + * efi earlycon needs to use early_memremap() to map the framebuffer.
> + * But early_memremap() is not usable for 'earlycon=efifb keep_bootcon',
> + * memremap() should be used instead. memremap() will be available after
> + * paging_init() which is earlier than initcall callbacks. Thus adding this
> + * early initcall function early_efi_map_fb() to map the whole efi framebuffer.
> + */
> +static int __init efi_earlycon_remap_fb(void)
> +{
> + /* bail if there is no bootconsole or it has been disabled already */
> + if (!earlycon_console || !(earlycon_console->flags & CON_ENABLED))
> + return 0;
> +
> + if (pgprot_val(fb_prot) == pgprot_val(PAGE_KERNEL))
> + efi_fb = memremap(fb_base, screen_info.lfb_size, MEMREMAP_WB);
> + else
> + efi_fb = memremap(fb_base, screen_info.lfb_size, MEMREMAP_WC);
> +
> + return efi_fb ? 0 : -ENOMEM;
> +}
> +early_initcall(efi_earlycon_remap_fb);
> +
> +static int __init efi_earlycon_unmap_fb(void)
> +{
> + /* unmap the bootconsole fb unless keep_bootcon has left it enabled */
> + if (efi_fb && !(earlycon_console->flags & CON_ENABLED))
> + memunmap(efi_fb);
> + return 0;
> +}
> +late_initcall(efi_earlycon_unmap_fb);
>
> static __ref void *efi_earlycon_map(unsigned long start, unsigned long len)
> {
> + if (efi_fb)
> + return efi_fb + start;
> +
> return early_memremap_prot(fb_base + start, len, pgprot_val(fb_prot));
> }
>
Actually, now I'm not so sure we really need the early map/unmap for
every line. If we switch from an early mapping to an ordinary mapping
at early_initcall() time, we can just map it once, and tear it down
when we do the ordinary memremap()
> static __ref void efi_earlycon_unmap(void *addr, unsigned long len)
> {
> + if (efi_fb)
> + return;
> +
> early_memunmap(addr, len);
> }
>
> @@ -201,6 +240,7 @@ static int __init efi_earlycon_setup(struct earlycon_device *device,
> efi_earlycon_scroll_up();
>
> device->con->write = efi_earlycon_write;
> + earlycon_console = device->con;
> return 0;
> }
> EARLYCON_DECLARE(efifb, efi_earlycon_setup);
> --
> 2.17.1
>
