Re: [Xen-devel] [PATCH v5 1/7] efi: Use early_mem*() instead of early_io*()

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Wed, Jun 18, 2014 at 01:17:09PM +0100, Matt Fleming wrote:
> (Pulling in Mark Salter for early_ioremap() knowledge)
>
> On Fri, 13 Jun, at 07:00:17PM, Daniel Kiper wrote:
> > Use early_mem*() instead of early_io*() because all mapped EFI regions
> > are true RAM not I/O regions. Additionally, I/O family calls do not work
> > correctly under Xen in our case. AIUI, early_io*() maps/unmaps real machine
> > addresses. However, all artificial EFI structures created under Xen live
> > in dom0 memory and should be mapped/unmapped using early_mem*() family
> > calls which map domain memory.
> >
> > Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> > ---
> >  arch/x86/platform/efi/efi.c |   42 
> > +++++++++++++++++++++---------------------
> >  drivers/firmware/efi/efi.c  |    4 ++--
> >  2 files changed, 23 insertions(+), 23 deletions(-)
> >
> > diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> > index 87fc96b..dd1e351 100644
> > --- a/arch/x86/platform/efi/efi.c
> > +++ b/arch/x86/platform/efi/efi.c
> > @@ -427,7 +427,7 @@ void __init efi_unmap_memmap(void)
> >  {
> >     clear_bit(EFI_MEMMAP, &efi.flags);
> >     if (memmap.map) {
> > -           early_iounmap(memmap.map, memmap.nr_map * memmap.desc_size);
> > +           early_memunmap(memmap.map, memmap.nr_map * memmap.desc_size);
> >             memmap.map = NULL;
> >     }
> >  }
> > @@ -467,12 +467,12 @@ static int __init efi_systab_init(void *phys)
> >                     if (!data)
> >                             return -ENOMEM;
> >             }
> > -           systab64 = early_ioremap((unsigned long)phys,
> > -                                    sizeof(*systab64));
> > +           systab64 = early_memremap((unsigned long)phys,
> > +                                           sizeof(*systab64));
>
> Please don't misalign the arguments :-( This makes the diff harder to
> read when all you're doing is changing the function call. You're
> indentation isn't an improvement.

I think that it improves readability a bit but if you wish I will not
do that in the future.

> As Matthew pointed out we may also need to access EFI mapped flash
> devices.

Right, but I think it does not change a lot in that case. Flash
is simply slower type of memory used as permanent storage.
Am I missing something?

> Now, the only difference between early_memremap() and early_ioremap(),
> at least on x86, is PAGE_KERNEL vs. PAGE_KERNEL_IO, where PAGE_KERNEL_IO
> has the additional _PAGE_BIT_IOMAP bit set in the pte. But that's a
> software bit for x86.
>
> So, even though this change should be harmless, it's not clear to me why
> this change is needed. You say "I/O family calls do not work correctly
> under Xen in our case", but could you provide some more explanation as
> to why they don't work correctly?

As I saw David provided better explanation. If you wish I could include
it in commit message.

Daniel

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