Re: [PATCH v3] efi/earlycon: Remap entire framebuffer after page initialization

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Fri, Nov 15, 2019 at 04:28:10PM +0000, Ard Biesheuvel wrote:
> On Fri, 15 Nov 2019 at 15:31, Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> >
> > When the commit 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk
> > into generic earlycon implementation") moved x86 specific EFI earlyprintk
> > implementation to shared location it also tweaked the behaviour. In particular
> > it dropped a trick with full framebuffer remapping after page initialization.
> > This lead to two regressions:
> > 1) very slow scrolling after page initialization;
> > 2) kernel hang when keep_bootcon parameter is being provided.
> >
> > Returning the trick back fixes #2 and mitigates, i.e. reduces the window when
> > slowness appears, #1 presumably due to eliminating heavy map()/unmap()
> > operations per each pixel line on the screen.

> > +/*
> > + * 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 early_efi_map_fb(void)
> > +{
> > +       if (!fb_base || !fb_size)
> > +               return NULL;
> > +
> 
> 'return 0' please.

Ah, sorry. Though I think we rather return -ENOVEV here.

> I'll test this on actual arm64 hardware somewhere next week, and queue
> it if it doesn't break anything (no need to resend for the above)

Thanks!

> > +       if (pgprot_val(fb_prot) == pgprot_val(PAGE_KERNEL))
> > +               efi_fb = memremap(fb_base, fb_size, MEMREMAP_WB);
> > +       else
> > +               efi_fb = memremap(fb_base, fb_size, MEMREMAP_WC);
> > +
> > +       return efi_fb ? 0 : -ENOMEM;
> > +}
> > +early_initcall(early_efi_map_fb);

-- 
With Best Regards,
Andy Shevchenko