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From: Elliott Mitchell <ehem+xen@m5p.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: Julien Grall <julien@xen.org>,
	Masami Hiramatsu <masami.hiramatsu@linaro.org>,
	xen-devel@lists.xenproject.org,
	Alex Benn??e <alex.bennee@linaro.org>,
	bertrand.marquis@arm.com, andre.przywara@arm.com,
	Julien Grall <jgrall@amazon.com>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [PATCH 0/4] xen/arm: Unbreak ACPI
Date: Mon, 12 Oct 2020 14:34:51 -0700
Message-ID: <20201012213451.GA89158@mattapan.m5p.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2010121157350.10386@sstabellini-ThinkPad-T480s>

On Mon, Oct 12, 2020 at 12:02:14PM -0700, Stefano Stabellini wrote:
> On Sat, 10 Oct 2020, Julien Grall wrote:
> > Therefore, I think the code should not try to find the STAO. Instead, it
> > should check whether the SPCR table is present.
> 
> Yes, that makes sense, but that brings me to the next question.
> 
> SPCR seems to be required by SBBR, however, Masami wrote that he could
> boot on a system without SPCR, which gets me very confused for two
> reasons:
> 
> 1) Why there is no SPCR? Isn't it supposed to be mandatory? Is it
> because there no UART on Masami's system?

I'm on different hardware, but some folks have setup Tianocore for it.
According to Documentation/arm64/acpi_object_usage.rst,
"Required: DSDT, FADT, GTDT, MADT, MCFG, RSDP, SPCR, XSDT".  Yet when
booting a Linux kernel directly on the hardware it lists APIC, BGRT,
CSRT, DSDT, DBG2, FACP, GTDT, PPTT, RSDP, and XSDT.

I don't know whether Linux's ACPI code omits mention of some required
tables and merely panics if they're absent.  Yet I'm speculating the list
of required tables has shrunk, SPCR is no longer required, and the
documentation is out of date.  Perhaps SPCR was required in early Linux
ACPI implementations, but more recent ones removed that requirement?

> 2) If there is no SPCR, how did Masami manage to boot Xen?
> I take without any serial output? Just with the framebuffer?

On my board the provided tables are sufficient to let Linux identify
ttyAMA0.  Linux's efifb driver finds the framebuffer and apparently has
it usable.


-- 
(\___(\___(\______          --=> 8-) EHM <=--          ______/)___/)___/)
 \BS (    |         ehem+sigmsg@m5p.com  PGP 87145445         |    )   /
  \_CS\   |  _____  -O #include <stddisclaimer.h> O-   _____  |   /  _/
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  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-26 20:55 Julien Grall
2020-09-26 20:55 ` [PATCH 1/4] xen/acpi: Rework acpi_os_map_memory() and acpi_os_unmap_memory() Julien Grall
2020-09-28  8:18   ` Jan Beulich
2020-09-28  9:58     ` Julien Grall
2020-09-28 10:09       ` Jan Beulich
2020-09-28 10:39         ` Julien Grall
2020-10-10  9:49           ` Julien Grall
2020-10-10 10:04             ` Julien Grall
2020-09-29 11:10   ` Rahul Singh
2020-10-01  0:06   ` Stefano Stabellini
2020-10-01 15:09     ` Julien Grall
2020-09-26 20:55 ` [PATCH 2/4] xen/arm: acpi: The fixmap area should always be cleared during failure/unmap Julien Grall
2020-09-29 11:13   ` Rahul Singh
2020-10-01  0:30   ` Stefano Stabellini
2020-10-01 15:14     ` Julien Grall
2020-09-26 20:55 ` [PATCH 3/4] xen/arm: Check if the platform is not using ACPI before initializing Dom0less Julien Grall
2020-09-29 11:17   ` Rahul Singh
2020-09-30 23:26   ` Stefano Stabellini
2020-09-26 20:55 ` [PATCH 4/4] xen/arm: Introduce fw_unreserved_regions() and use it Julien Grall
2020-09-30 23:40   ` Stefano Stabellini
2020-10-01 15:34     ` Julien Grall
2020-09-27  1:47 ` [PATCH 0/4] xen/arm: Unbreak ACPI Elliott Mitchell
2020-09-29 15:28   ` Elliott Mitchell
2020-09-28  6:47 ` Masami Hiramatsu
2020-09-28 13:00   ` Masami Hiramatsu
2020-10-16 22:33     ` Xen-ARM EFI/ACPI problems (was: Re: [PATCH 0/4] xen/arm: Unbreak ACPI) Elliott Mitchell
2020-10-17  5:12       ` Elliott Mitchell
2020-10-08 18:39   ` [PATCH 0/4] xen/arm: Unbreak ACPI Elliott Mitchell
2020-10-09  9:39     ` Julien Grall
2020-10-09 14:22       ` Elliott Mitchell
2020-10-09 18:15         ` Julien Grall
2020-10-09 22:36           ` Elliott Mitchell
2020-10-09 21:49   ` Elliott Mitchell
2020-10-10 11:02   ` Julien Grall
2020-10-12 19:02     ` Stefano Stabellini
2020-10-12 21:34       ` Elliott Mitchell [this message]
2020-10-14  1:06         ` Stefano Stabellini
2020-10-14  1:37           ` Elliott Mitchell
2020-10-14 17:47             ` Julien Grall
2020-10-15 18:00               ` Stefano Stabellini
2020-10-14 17:44       ` Julien Grall
2020-09-29 11:10 ` Rahul Singh
2020-09-29 15:29 ` Alex Bennée
2020-09-29 17:07   ` Julien Grall
2020-09-29 21:11     ` Alex Bennée
2020-09-29 23:39       ` André Przywara
2020-09-30  8:51         ` Alex Bennée
2020-09-30 10:35         ` Julien Grall
2020-09-30  9:42       ` Julien Grall
2020-09-30 10:38         ` Alex Bennée
2020-09-30 11:10           ` Julien Grall

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