On Thu, 5 Dec 2019 at 17:16, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>
> 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()
>
Never mind ... early_memremap() cannot map the entire framebuffer in one go.
>
> > 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
> >
