linux-kernel - Re: [PATCH v2 13/36] irqchip/gic-v4.1: Don't use the VPE proxy if RVPEID is set

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Date:   Fri, 1 Nov 2019 19:05:56 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Marc Zyngier <maz@...nel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-kernel@...r.kernel.org>
CC:     Eric Auger <eric.auger@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "Andrew Murray" <Andrew.Murray@....com>,
        Jayachandran C <jnair@...vell.com>,
        "Robert Richter" <rrichter@...vell.com>
Subject: Re: [PATCH v2 13/36] irqchip/gic-v4.1: Don't use the VPE proxy if
 RVPEID is set

Hi Marc,

On 2019/10/27 22:42, Marc Zyngier wrote:
> The infamous VPE proxy device isn't used with GICv4.1 because:
> - we can invalidate any LPI from the DirectLPI MMIO interface
> - the ITS and redistributors understand the life cycle of
>    the doorbell, so we don't need to enable/disable it all
>    the time
> 
> So let's escape early from the proxy related functions.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>

Reviewed-by: Zenghui Yu <yuzenghui@...wei.com>

> ---
>   drivers/irqchip/irq-gic-v3-its.c | 23 ++++++++++++++++++++++-
>   1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 220d490d516e..999e61a9b2c3 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -3069,7 +3069,7 @@ static const struct irq_domain_ops its_domain_ops = {
>   /*
>    * This is insane.
>    *
> - * If a GICv4 doesn't implement Direct LPIs (which is extremely
> + * If a GICv4.0 doesn't implement Direct LPIs (which is extremely
>    * likely), the only way to perform an invalidate is to use a fake
>    * device to issue an INV command, implying that the LPI has first
>    * been mapped to some event on that device. Since this is not exactly
> @@ -3077,9 +3077,18 @@ static const struct irq_domain_ops its_domain_ops = {
>    * only issue an UNMAP if we're short on available slots.
>    *
>    * Broken by design(tm).
> + *
> + * GICv4.1 actually mandates that we're able to invalidate by writing to a
> + * MMIO register. It doesn't implement the whole of DirectLPI, but that's
> + * good enough. And most of the time, we don't even have to invalidate
> + * anything, so that's actually pretty good!

I can't understand the meaning of this last sentence. May I ask for an
explanation? :)


Thanks,
Zenghui

>    */
>   static void its_vpe_db_proxy_unmap_locked(struct its_vpe *vpe)
>   {
> +	/* GICv4.1 doesn't use a proxy, so nothing to do here */
> +	if (gic_rdists->has_rvpeid)
> +		return;
> +
>   	/* Already unmapped? */
>   	if (vpe->vpe_proxy_event == -1)
>   		return;
> @@ -3102,6 +3111,10 @@ static void its_vpe_db_proxy_unmap_locked(struct its_vpe *vpe)
>   
>   static void its_vpe_db_proxy_unmap(struct its_vpe *vpe)
>   {
> +	/* GICv4.1 doesn't use a proxy, so nothing to do here */
> +	if (gic_rdists->has_rvpeid)
> +		return;
> +
>   	if (!gic_rdists->has_direct_lpi) {
>   		unsigned long flags;
>   
> @@ -3113,6 +3126,10 @@ static void its_vpe_db_proxy_unmap(struct its_vpe *vpe)
>   
>   static void its_vpe_db_proxy_map_locked(struct its_vpe *vpe)
>   {
> +	/* GICv4.1 doesn't use a proxy, so nothing to do here */
> +	if (gic_rdists->has_rvpeid)
> +		return;
> +
>   	/* Already mapped? */
>   	if (vpe->vpe_proxy_event != -1)
>   		return;
> @@ -3135,6 +3152,10 @@ static void its_vpe_db_proxy_move(struct its_vpe *vpe, int from, int to)
>   	unsigned long flags;
>   	struct its_collection *target_col;
>   
> +	/* GICv4.1 doesn't use a proxy, so nothing to do here */
> +	if (gic_rdists->has_rvpeid)
> +		return;
> +
>   	if (gic_rdists->has_direct_lpi) {
>   		void __iomem *rdbase;
>   
>