linux-kernel - Re: [PATCH 2/3] irqchip/gic-v3: Detect LPI invalidation MMIO registers

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Message-ID: <20220316145141.44d20486@slackpad.lan>
Date:   Wed, 16 Mar 2022 14:51:58 +0000
From:   Andre Przywara <andre.przywara@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Auger <eric.auger@...hat.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH 2/3] irqchip/gic-v3: Detect LPI invalidation MMIO
 registers

On Tue, 15 Mar 2022 16:50:33 +0000
Marc Zyngier <maz@...nel.org> wrote:

Hi,

> Since GICv4.1, an implementation can offer the same MMIO-based
> implementation as DirectLPI, only with an ITS. Given that this
> can be hugely beneficial for workloads that are very LPI masking
> heavy (although these workloads are admitedly a bit odd).
> 
> Interestingly, this is independent of RVPEI, which only *implies*
> the functionnality.
> 
> So let's detect whether the implementation has GICR_CTLR.IR set,
> and propagate this as DirectLPI to the ITS driver.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  drivers/irqchip/irq-gic-v3.c       | 15 +++++++++++----
>  include/linux/irqchip/arm-gic-v3.h |  2 ++
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 736163d36b13..363bfe172033 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -918,7 +918,11 @@ static int gic_populate_rdist(void)
>  static int __gic_update_rdist_properties(struct redist_region *region,
>  					 void __iomem *ptr)
>  {
> -	u64 typer = gic_read_typer(ptr + GICR_TYPER);
> +	u64 typer;
> +	u32 ctlr;
> +
> +	typer = gic_read_typer(ptr + GICR_TYPER);
> +	ctlr = readl_relaxed(ptr + GICR_CTLR);

Is there any reason you didn't keep this together? I thought this was
recommended, in general?

>  
>  	/* Boot-time cleanip */
>  	if ((typer & GICR_TYPER_VLPIS) && (typer & GICR_TYPER_RVPEID)) {
> @@ -941,6 +945,7 @@ static int __gic_update_rdist_properties(struct redist_region *region,
>  	/* RVPEID implies some form of DirectLPI, no matter what the doc says... :-/ */
>  	gic_data.rdists.has_rvpeid &= !!(typer & GICR_TYPER_RVPEID);
>  	gic_data.rdists.has_direct_lpi &= (!!(typer & GICR_TYPER_DirectLPIS) |
> +					   !!(ctlr & GICR_CTLR_IR) |

So this means that has_direct_lpi is not really correct anymore, as the
IR bit only covers the INVL and SYNCR registers, not the GICR_SETLPIR
and GICR_CLRLPIR registers, if I understand the spec correctly?

But I guess this is nitpicking, as we don't use direct LPIs at all in
Linux? And I guess the target is lpi_update_config(), which now doesn't
need the command queue anymore?

Maybe this could be clarified in the commit message?

>  					   gic_data.rdists.has_rvpeid);
>  	gic_data.rdists.has_vpend_valid_dirty &= !!(typer & GICR_TYPER_DIRTY);
>  
> @@ -962,7 +967,11 @@ static void gic_update_rdist_properties(void)
>  	gic_iterate_rdists(__gic_update_rdist_properties);
>  	if (WARN_ON(gic_data.ppi_nr == UINT_MAX))
>  		gic_data.ppi_nr = 0;
> -	pr_info("%d PPIs implemented\n", gic_data.ppi_nr);
> +	pr_info("GICv3 features: %d PPIs, %s%s\n",

I like having that on one line, but it looks a bit odd with the
trailing comma when we have neither RSS nor DirectLPI.
What about:
	pr_info("GICv3 features: %d PPIs%s%s\n",
	gic_data.ppi_nr,
	gic_data.has_rss ? ", RSS" : "",
	gic_data.rdists.has_direct_lpi ? ", DirectLPI" : "");

> +		gic_data.ppi_nr,
> +		gic_data.has_rss ? "RSS " : "",
> +		gic_data.rdists.has_direct_lpi ? "DirectLPI " : "");
> +	
>  	if (gic_data.rdists.has_vlpis)
>  		pr_info("GICv4 features: %s%s%s\n",
>  			gic_data.rdists.has_direct_lpi ? "DirectLPI " : "",
> @@ -1797,8 +1806,6 @@ static int __init gic_init_bases(void __iomem *dist_base,
>  	irq_domain_update_bus_token(gic_data.domain, DOMAIN_BUS_WIRED);
>  
>  	gic_data.has_rss = !!(typer & GICD_TYPER_RSS);
> -	pr_info("Distributor has %sRange Selector support\n",
> -		gic_data.has_rss ? "" : "no ");
>  
>  	if (typer & GICD_TYPER_MBIS) {
>  		err = mbi_init(handle, gic_data.domain);
> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
> index 12d91f0dedf9..aeb8ced53880 100644
> --- a/include/linux/irqchip/arm-gic-v3.h
> +++ b/include/linux/irqchip/arm-gic-v3.h
> @@ -127,6 +127,8 @@
>  #define GICR_PIDR2			GICD_PIDR2
>  
>  #define GICR_CTLR_ENABLE_LPIS		(1UL << 0)
> +#define GICR_CTLR_IR			(1UL << 1)
> +#define GICR_CTLR_CES			(1UL << 2)

As Oliver (and you) already pointed out, this is swapped.

Cheers,
Andre

>  #define GICR_CTLR_RWP			(1UL << 3)
>  
>  #define GICR_TYPER_CPU_NUMBER(r)	(((r) >> 8) & 0xffff)