Re: [PATCH] riscv: acpi: update FADT revision check to 6.6

From: Yao Zi <me@ziyao.cc>
To: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>,
	"rom.wang" <r4o5m6e8o@163.com>
Cc: linux-kernel@vger.kernel.org, Yufeng Wang <wangyufeng@kylinos.cn>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Conor Dooley <conor.dooley@microchip.com>,
	Ryan Roberts <ryan.roberts@arm.com>,
	Sean Chang <seanwascoding@gmail.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH] riscv: acpi: update FADT revision check to 6.6
Date: Thu, 5 Mar 2026 14:19:37 +0000	[thread overview]
Message-ID: <aamQ-Xdfuh6PramC@pie> (raw)
In-Reply-To: <f4ba06cb-a0d8-423c-b1bc-0257625eea00@canonical.com>

On Thu, Mar 05, 2026 at 02:00:50PM +0100, Heinrich Schuchardt wrote:
> On 3/5/26 10:14, rom.wang wrote:
> > From: Yufeng Wang <wangyufeng@kylinos.cn>
> > 
> > ACPI 6.6 is required for RISC-V as it introduces RISC-V specific
> > tables such as RHCT (RISC-V Hart Capabilities Table) and
> > RIMT (RISC-V I/O Mapping Table).
> > 
> > Update the FADT revision check from 6.5 to 6.6 and remove
> > the TODO comment since ACPI 6.6 has been officially released.
> 
> If I understand the change correctly:
> 
> After the patch QEMU v10.0.0 will stop to boot Linux via ACPI.
> QEMU v10.1.0 will be supported as it indicates revision 6.6.
> See function build_fadt_rev6() in qemu/hw/riscv/virt-acpi-build.c.

I don't think so, this condition only decides whether an error is
printed as firmware bug when the kernel encountering pre-6.6 FADTs,
and the rest boot process should remain untouched. So it in fact breaks
nothing.

> For Ubuntu this is not an issue as it is on QEMU 10.1 on recent releases
> (https://launchpad.net/ubuntu/+source/qemu).
> Fedora 43 also has QEMU 10.1
> (https://packages.fedoraproject.org/pkgs/qemu/qemu/).
> Suse Tumbleweed has 10.2.1 (https://software.opensuse.org/package/qemu).
> 
> Stable Debian Trixie using 10.0 will be impacted
> (https://packages.debian.org/trixie/qemu-system-misc). Debian Testing has
> 10.2.
> 
> Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> 
> > 
> > Signed-off-by: Yufeng Wang <wangyufeng@kylinos.cn>
> > ---
> >   arch/riscv/kernel/acpi.c | 10 +++++-----
> >   1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/riscv/kernel/acpi.c b/arch/riscv/kernel/acpi.c
> > index 71698ee11621..ff681db9f4f1 100644
> > --- a/arch/riscv/kernel/acpi.c
> > +++ b/arch/riscv/kernel/acpi.c
> > @@ -85,12 +85,12 @@ static int __init acpi_fadt_sanity_check(void)
> >   	 * The revision in the table header is the FADT's Major revision. The
> >   	 * FADT also has a minor revision, which is stored in the FADT itself.
> >   	 *
> > -	 * TODO: Currently, we check for 6.5 as the minimum version to check
> > -	 * for HW_REDUCED flag. However, once RISC-V updates are released in
> > -	 * the ACPI spec, we need to update this check for exact minor revision
> > +	 * ACPI 6.6 is required for RISC-V as it introduces RISC-V specific
> > +	 * tables such as RHCT (RISC-V Hart Capabilities Table) and RIMT
> > +	 * (RISC-V I/O Mapping Table).
> >   	 */
> > -	if (table->revision < 6 || (table->revision == 6 && fadt->minor_revision < 5))
> > -		pr_err(FW_BUG "Unsupported FADT revision %d.%d, should be 6.5+\n",
> > +	if (table->revision < 6 || (table->revision == 6 && fadt->minor_revision < 6))
> > +		pr_err(FW_BUG "Unsupported FADT revision %d.%d, should be 6.6+\n",
> >   		       table->revision, fadt->minor_revision);

Here pr_err() is the only statement enclosed by the if.

> >   	if (!(fadt->flags & ACPI_FADT_HW_REDUCED)) {

Reviewed-by: Yao Zi <me@ziyao.cc>

Regards,
Yao Zi

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