Re: [PATCH v2 1/2] arm64: Move Mediatek GIC quirk handling from irqchip to core

From: Marc Zyngier <maz@kernel.org>
To: Douglas Anderson <dianders@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Chen-Yu Tsai <wenst@chromium.org>,
	Amit Daniel Kachhap <amit.kachhap@arm.com>,
	AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	James Morse <james.morse@arm.com>,
	Joey Gouly <joey.gouly@arm.com>, Mark Brown <broonie@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org
Subject: Re: [PATCH v2 1/2] arm64: Move Mediatek GIC quirk handling from irqchip to core
Date: Tue, 07 Nov 2023 15:57:05 +0000	[thread overview]
Message-ID: <86cywl1rqm.wl-maz@kernel.org> (raw)
In-Reply-To: <20231107072651.v2.1.Ide945748593cffd8ff0feb9ae22b795935b944d6@changeid>

On Tue, 07 Nov 2023 15:26:56 +0000,
Douglas Anderson <dianders@chromium.org> wrote:
> 
> In commit 44bd78dd2b88 ("irqchip/gic-v3: Disable pseudo NMIs on
> Mediatek devices w/ firmware issues") we added a method for detecting
> Mediatek devices with broken firmware and disabled pseudo-NMI. While
> that worked, it didn't address the problem at a deep enough level.
> 
> The fundamental issue with this broken firmware is that it's not
> saving and restoring several important GICR registers. The current
> list is believed to be:
> * GICR_NUM_IPRIORITYR
> * GICR_CTLR
> * GICR_ISPENDR0
> * GICR_ISACTIVER0
> * GICR_NSACR
> 
> Pseudo-NMI didn't work because it was the only thing (currently) in
> the kernel that relied on the broken registers, so forcing pseudo-NMI
> off was an effective fix. However, it could be observed that calling
> system_uses_irq_prio_masking() on these systems still returned
> "true". That caused confusion and led to the need for
> commit a07a59415217 ("arm64: smp: avoid NMI IPIs with broken MediaTek
> FW"). It's worried that the incorrect value returned by
> system_uses_irq_prio_masking() on these systems will continue to
> confuse future developers.
> 
> Let's fix the issue a little more completely by disabling IRQ
> priorities at a deeper level in the kernel. Once we do this we can
> revert some of the other bits of code dealing with this quirk.
> 
> This includes a partial revert of commit 44bd78dd2b88
> ("irqchip/gic-v3: Disable pseudo NMIs on Mediatek devices w/ firmware
> issues"). This isn't a full revert because it leaves some of the
> changes to the "quirks" structure around in case future code needs it.
> 
> Suggested-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

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