RE: [PATCH v3 1/5] ACPI: change __init to __ref for early_acpi_os_unmap_memory()

[Zheng, Lv]

Hi,

> From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Zheng, Lv
> Subject: RE: [PATCH v3 1/5] ACPI: change __init to __ref for
> early_acpi_os_unmap_memory()
> 
> Hi,
> 
> > -----Original Message-----
> > From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Aleksey Makarov
> > Sent: Tuesday, February 16, 2016 2:05 AM
> > To: linux-acpi@xxxxxxxxxxxxxxx
> > Cc: linux-serial@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> > kernel@xxxxxxxxxxxxxxxxxxx; Aleksey Makarov <aleksey.makarov@xxxxxxxxxx>;
> > Russell King <linux@xxxxxxxxxxxxxxxx>; Greg Kroah-Hartman
> > <gregkh@xxxxxxxxxxxxxxxxxxx>; Rafael J . Wysocki <rjw@xxxxxxxxxxxxx>; Leif
> > Lindholm <leif.lindholm@xxxxxxxxxx>; Graeme Gregory
> > <graeme.gregory@xxxxxxxxxx>; Al Stone <ahs3@xxxxxxxxxx>; Christopher
> > Covington <cov@xxxxxxxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>
> > Subject: [PATCH v3 1/5] ACPI: change __init to __ref for
> > early_acpi_os_unmap_memory()
> >
> > early_acpi_os_unmap_memory() is marked as __init because it calls
> > __acpi_unmap_table(), but only when acpi_gbl_permanent_mmap is not set.
> >
> > acpi_gbl_permanent_mmap is set in __init acpi_early_init()
> > so it is safe to call early_acpi_os_unmap_memory() from anywhere
> >
> > We need this function to be non-__init because we need access to
> > some tables at unpredictable time--it may be before or after
> > acpi_gbl_permanent_mmap is set.  For example, SPCR (Serial Port Console
> > Redirection) table is needed each time a new console is registered.
> > It can be quite early (console_initcall) or when a module is inserted.
> > When this table accessed before acpi_gbl_permanent_mmap is set,
> > the pointer should be unmapped.  This is exactly what this function
> > does.
> [Lv Zheng]
> Why don't you use another API instead of early_acpi_os_unmap_memory() in
> case you want to unmap things in any cases.
> acpi_os_unmap_memory() should be the one to match this purpose.
> It checks acpi_gbl_ppermanent_mmap in acpi_os_unmap_iomem().
> And in fact early_acpi_os_unmap_memory() should be removed.
[Lv Zheng] 
One more thing is:
If you can't switch your driver to use acpi_os_unmap_memory() instead of early_acpi_os_unmap_memory(),
then it implies that your driver does have a defect.

There is an early bootup requirement in Linux.
Maps acquired during the early stage should be freed by the driver during the early stage.
And the driver should re-acquire the memory map after booting.

This is because, during early bootup stage, there are only limited slots available for drivers to map memory.
So by changing __init to __ref here, you probably will hide many such defects.
And solving issues in this way doesn't seem to be an improvement.

Thanks and best regards
-Lv

> 
> Thanks and best regards
> -Lv
> 
> >
> > Signed-off-by: Aleksey Makarov <aleksey.makarov@xxxxxxxxxx>
> > ---
> >  drivers/acpi/osl.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> > index 67da6fb..8a552cd 100644
> > --- a/drivers/acpi/osl.c
> > +++ b/drivers/acpi/osl.c
> > @@ -497,7 +497,11 @@ void __ref acpi_os_unmap_memory(void *virt,
> > acpi_size size)
> >  }
> >  EXPORT_SYMBOL_GPL(acpi_os_unmap_memory);
> >
> > -void __init early_acpi_os_unmap_memory(void __iomem *virt, acpi_size
> size)
> > +/*
> > + * acpi_gbl_permanent_mmap is set in __init acpi_early_init()
> > + * so it is safe to call early_acpi_os_unmap_memory() from anywhere
> > + */
> > +void __ref early_acpi_os_unmap_memory(void __iomem *virt, acpi_size
> size)
> >  {
> >  	if (!acpi_gbl_permanent_mmap)
> >  		__acpi_unmap_table(virt, size);
> > --
> > 2.7.1
> >
> > --
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