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    Subject[PATCH AUTOSEL 5.4 029/187] efi/earlycon: Remap entire framebuffer after page initialization
    Date
    From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

    [ Upstream commit b418d660bb9798d2249ac6a46c844389ef50b6a5 ]

    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.

    [ ardb: ensure efifb is unmapped again unless keep_bootcon is in effect. ]
    [ mingo: speling fixes. ]

    Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
    Cc: Arvind Sankar <nivedita@alum.mit.edu>
    Cc: Bhupesh Sharma <bhsharma@redhat.com>
    Cc: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
    Cc: linux-efi@vger.kernel.org
    Fixes: 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation")
    Link: https://lkml.kernel.org/r/20191206165542.31469-7-ardb@kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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..d4077db6dc97 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));
    }

    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);
    --
    2.20.1
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