linux-kernel - Re: [PATCH 04/14] x86, ACPI: make acpi override finding work with 32bit flat mode

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Date:	Thu, 7 Mar 2013 23:06:51 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Renninger <trenn@...e.de>,
	Tang Chen <tangchen@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
	Jacob Shin <jacob.shin@....com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 04/14] x86, ACPI: make acpi override finding work with
 32bit flat mode

Hello, Yinghai.

On Thu, Mar 07, 2013 at 10:57:21PM -0800, Yinghai Lu wrote:
> On Thu, Mar 7, 2013 at 9:50 PM, Tejun Heo <tj@...nel.org> wrote:
> > On Thu, Mar 07, 2013 at 08:58:30PM -0800, Yinghai Lu wrote:
> >> We will find acpi tables in initrd during head_32.S in 32bit flat mode.
> >>
> >> So need acpi_initrd_override_find could take phys directly.
> >
> > The patch description doesn't explain even half of what's going on.
> 
> hope HPA could understand.
> 
> Access initrd before relocate_initrd and init_memory mapping.

I really hope the changelogs were better.  Eh well...

> >> -/* All but ACPI_SIG_RSDP and ACPI_SIG_FACS: */
> >> -static const char * const table_sigs[] = {
> >> -     ACPI_SIG_BERT, ACPI_SIG_CPEP, ACPI_SIG_ECDT, ACPI_SIG_EINJ,
> >> -     ACPI_SIG_ERST, ACPI_SIG_HEST, ACPI_SIG_MADT, ACPI_SIG_MSCT,
> >> -     ACPI_SIG_SBST, ACPI_SIG_SLIT, ACPI_SIG_SRAT, ACPI_SIG_ASF,
> >> -     ACPI_SIG_BOOT, ACPI_SIG_DBGP, ACPI_SIG_DMAR, ACPI_SIG_HPET,
> >> -     ACPI_SIG_IBFT, ACPI_SIG_IVRS, ACPI_SIG_MCFG, ACPI_SIG_MCHI,
> >> -     ACPI_SIG_SLIC, ACPI_SIG_SPCR, ACPI_SIG_SPMI, ACPI_SIG_TCPA,
> >> -     ACPI_SIG_UEFI, ACPI_SIG_WAET, ACPI_SIG_WDAT, ACPI_SIG_WDDT,
> >> -     ACPI_SIG_WDRT, ACPI_SIG_DSDT, ACPI_SIG_FADT, ACPI_SIG_PSDT,
> >> -     ACPI_SIG_RSDT, ACPI_SIG_XSDT, ACPI_SIG_SSDT, NULL };
> >
> > Why is this table made a stack variable?  What's the benefit of doing
> > that?
> 
> so I do need to switch global variables to phys and access it.

I can't really understand what your response means.  Can you please
elaborate?

> > Is it really necessary to make the function take both virtual and
> > physical addresses?  Can't we just make the function take phys_addr_t
> > and update everyone to call with physaddr?  Also @is_phys isn't simple
> > address switch.  It also changes error reporting.  If you're gonna
> > keep @is_phys, let's at least write up a function comment explaining
> > what's going on and why we need it.  But, really, if at all possible,
> > let's change the function to take single type of argument and
> > predicate error message printing on something else (e.g. early printk
> > initialized or whatever).
> 
> yes, one for 32bit from head_32.S, phys.
> one for 64bit from head64.c. with _va.

head64.c can't call with phys?  Why not?

> Not sure if I could use early_printk from head_32.S, as Fenghua does
> not print out
> from microcode updating early in the same parts.

ISTR it works but it doens't have to (although it would be much nicer
if it did).  You can test whether printk is online and skip if it
isn't online yet.

Thanks.

-- 
tejun
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