Received-SPF: pass (google.com: domain of linux-kernel+bounces-33982-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Mon, 22 Jan 2024 18:27:09 +0000
Message-ID: <86plxt8br6.wl-maz@kernel.org>
From: Marc Zyngier <maz@kernel.org>
To: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	Robin Murphy <robin.murphy@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-acpi@vger.kernel.org,
	acpica-devel@lists.linux.dev,
	Fang Xiang <fangxiang3@xiaomi.com>,
	Robert Moore <robert.moore@intel.com>
Subject: Re: [PATCH v4 3/3] irqchip/gic-v3: Enable non-coherent redistributors/ITSes ACPI probing
In-Reply-To: <Za6VPE76yiR+lb91@lpieralisi>
References: <20230905104721.52199-1-lpieralisi@kernel.org>
	<20231227110038.55453-1-lpieralisi@kernel.org>
	<20231227110038.55453-4-lpieralisi@kernel.org>
	<Za6VPE76yiR+lb91@lpieralisi>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue)
 FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/29.1
 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO)
Precedence: bulk
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset=US-ASCII

On Mon, 22 Jan 2024 16:18:04 +0000,
Lorenzo Pieralisi <lpieralisi@kernel.org> wrote:
> 
> On Wed, Dec 27, 2023 at 12:00:38PM +0100, Lorenzo Pieralisi wrote:
> 
> [...]
> 
> > @@ -2380,6 +2385,10 @@ gic_acpi_parse_madt_gicc(union acpi_subtable_headers *header,
> >  		return -ENOMEM;
> >  	gic_request_region(gicc->gicr_base_address, size, "GICR");
> >  
> > +	if (gic_acpi_non_coherent_flag(gicc->flags,
> > +				       ACPI_MADT_GICC_NON_COHERENT))
> > +		gic_data.rdists.flags |= RDIST_FLAGS_FORCE_NON_SHAREABLE;
> > +
> 
> Quick question before reposting it. We run this function for
> every GICC entry, I didn't add a check to make sure all GICC
> entries have the same flag value, please let me know if that's
> OK.
> 
> I don't think there is a point in keeping a live variable across
> calls to set the flag once for all either.

I don't think that's useful. Once we see the flag being set, we'll
enforce the non-coherency. If it wasn't set before, it's because it
wasn't necessary.

If one day we find a firmware that only randomly exposes the flag,
we'll treat it as a quirk.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.