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

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Message-ID: <9b2e37a0-32ee-4aa4-99e8-d37103674847@collabora.com>
Date:   Tue, 7 Nov 2023 17:29:58 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Douglas Anderson <dianders@...omium.org>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Chen-Yu Tsai <wenst@...omium.org>
Cc:     Amit Daniel Kachhap <amit.kachhap@....com>,
        James Morse <james.morse@....com>,
        Joey Gouly <joey.gouly@....com>,
        Mark Brown <broonie@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2 1/2] arm64: Move Mediatek GIC quirk handling from
 irqchip to core

Il 07/11/23 16:26, Douglas Anderson ha scritto:
> 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@....com>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
> Changes in v2:
> - Just detect the quirk once at init time.
> - Fixed typo in subject: s/GiC/GIC.
> - Squash in ("Remove Mediatek pseudo-NMI firmware quirk handling").
> 
>   arch/arm64/kernel/cpufeature.c | 46 ++++++++++++++++++++++++++++------
>   drivers/irqchip/irq-gic-v3.c   | 22 +---------------
>   2 files changed, 39 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index f6b2e2906fc9..928124ea2e96 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -999,6 +999,37 @@ static void init_32bit_cpu_features(struct cpuinfo_32bit *info)
>   	init_cpu_ftr_reg(SYS_MVFR2_EL1, info->reg_mvfr2);
>   }
>   
> +#ifdef CONFIG_ARM64_PSEUDO_NMI
> +static bool enable_pseudo_nmi;
> +
> +static int __init early_enable_pseudo_nmi(char *p)
> +{
> +	return kstrtobool(p, &enable_pseudo_nmi);
> +}
> +early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
> +
> +static __init void detect_system_supports_pseudo_nmi(void)
> +{
> +	struct device_node *np;
> +
> +	if (!enable_pseudo_nmi)
> +		return;
> +
> +	/*
> +	 * Detect broken Mediatek firmware that doesn't properly save and

s/Mediatek/MediaTek/g

Apart from that,

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

On MT8195, MT8192, MT8186:
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>