Re: [PATCH 1/3] irqchip/gic-v3: Fix GICR_CTLR.RWP polling

From: Andre Przywara <andre.przywara@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Eric Auger <eric.auger@redhat.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/3] irqchip/gic-v3: Fix GICR_CTLR.RWP polling
Date: Wed, 16 Mar 2022 14:51:02 +0000	[thread overview]
Message-ID: <20220316145102.28ad0a74@slackpad.lan> (raw)
In-Reply-To: <20220315165034.794482-2-maz@kernel.org>

On Tue, 15 Mar 2022 16:50:32 +0000
Marc Zyngier <maz@kernel.org> wrote:

> It turns out that our polling of RWP is totally wrong when checking
> for it in the redistributors, as we test the *distributor* bit index,
> whereas it is a different bit number in the RDs... Oopsie boo.
> 
> This is embarassing. Not only because it is wrong, but also because
> it took *8 years* to notice the blunder...

Indeed, I wonder why we didn't see issues before. I guess it's either
the UWP bit at position GICR_CTLR[31] having a similar implementation,
or the MMIO access alone providing enough delay for the writes to
finish.

Anyway:

> Just fix the damn thing.
> 
> Fixes: 021f653791ad ("irqchip: gic-v3: Initial support for GICv3")
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Cc: stable@vger.kernel.org

Reviewed-by: Andre Przywara <andre.przywara@arm.com>

Cheers,
Andre

> ---
>  drivers/irqchip/irq-gic-v3.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 5e935d97207d..736163d36b13 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -206,11 +206,11 @@ static inline void __iomem *gic_dist_base(struct irq_data *d)
>  	}
>  }
>  
> -static void gic_do_wait_for_rwp(void __iomem *base)
> +static void gic_do_wait_for_rwp(void __iomem *base, u32 bit)
>  {
>  	u32 count = 1000000;	/* 1s! */
>  
> -	while (readl_relaxed(base + GICD_CTLR) & GICD_CTLR_RWP) {
> +	while (readl_relaxed(base + GICD_CTLR) & bit) {
>  		count--;
>  		if (!count) {
>  			pr_err_ratelimited("RWP timeout, gone fishing\n");
> @@ -224,13 +224,13 @@ static void gic_do_wait_for_rwp(void __iomem *base)
>  /* Wait for completion of a distributor change */
>  static void gic_dist_wait_for_rwp(void)
>  {
> -	gic_do_wait_for_rwp(gic_data.dist_base);
> +	gic_do_wait_for_rwp(gic_data.dist_base, GICD_CTLR_RWP);
>  }
>  
>  /* Wait for completion of a redistributor change */
>  static void gic_redist_wait_for_rwp(void)
>  {
> -	gic_do_wait_for_rwp(gic_data_rdist_rd_base());
> +	gic_do_wait_for_rwp(gic_data_rdist_rd_base(), GICR_CTLR_RWP);
>  }
>  
>  #ifdef CONFIG_ARM64