[RFC] irqchip/gic-v3: Correct the usage of GICD_CTLR's RWP field
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Message ID 1557720954-6592-1-git-send-email-yuzenghui@huawei.com
State New, archived
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  • [RFC] irqchip/gic-v3: Correct the usage of GICD_CTLR's RWP field
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Commit Message

Zenghui Yu May 13, 2019, 4:15 a.m. UTC
As per ARM IHI 0069D, GICD_CTLR's RWP field tracks updates to:

	GICD_CTLR's Group Enable bits, for transitions from 1 to 0 only
	GICD_CTLR's ARE bits, E1NWF bit and DS bit (if we have)
	GICD_ICENABLER<n>

We seemed use this field in an inappropriate way, somewhere in the
GIC-v3 driver. For some examples:

In gic_set_affinity(), if the interrupt was not enabled, we only need
to write GICD_IROUTER<n> with the appropriate mpidr value. Updates to
GICD_IROUTER will not be tracked by RWP field, and we can remove the
unnecessary RWP waiting.

In gic_dist_init(), we "Enable distributor with ARE, Group1" by writing
to GICD_CTLR, and we should use gic_dist_wait_for_rwp() here.

These two are obvious cases, and there are some other cases where we don't
need to do RWP waiting, such as in gic_configure_irq() and gic_poke_irq().
But too many modifications makes me not confident. It's hard for me to say
whether this patch is doing the right thing and how does the RWP waiting
affect the system, thus RFC.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 drivers/irqchip/irq-gic-v3.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

Comments

Andre Przywara May 13, 2019, 8:37 a.m. UTC | #1
On Mon, 13 May 2019 04:15:54 +0000
Zenghui Yu <yuzenghui@huawei.com> wrote:

Hi,

> As per ARM IHI 0069D, GICD_CTLR's RWP field tracks updates to:
> 
> 	GICD_CTLR's Group Enable bits, for transitions from 1 to 0 only
> 	GICD_CTLR's ARE bits, E1NWF bit and DS bit (if we have)
> 	GICD_ICENABLER<n>
> 
> We seemed use this field in an inappropriate way, somewhere in the
> GIC-v3 driver. For some examples:
> 
> In gic_set_affinity(), if the interrupt was not enabled, we only need
> to write GICD_IROUTER<n> with the appropriate mpidr value. Updates to
> GICD_IROUTER will not be tracked by RWP field, and we can remove the
> unnecessary RWP waiting.

I am not sure this is the proper fix, see below inline.

> In gic_dist_init(), we "Enable distributor with ARE, Group1" by writing
> to GICD_CTLR, and we should use gic_dist_wait_for_rwp() here.

That looks reasonable, yes.

> These two are obvious cases, and there are some other cases where we don't
> need to do RWP waiting, such as in gic_configure_irq() and gic_poke_irq().
> But too many modifications makes me not confident. It's hard for me to say
> whether this patch is doing the right thing and how does the RWP waiting
> affect the system, thus RFC.

So did you actually see a problem, and this patch fixes it? Or was this
just discovered by code inspection and comparing to the spec?

> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
> ---
>  drivers/irqchip/irq-gic-v3.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 15e55d3..8d63950 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -600,6 +600,7 @@ static void __init gic_dist_init(void)
>  	/* Enable distributor with ARE, Group1 */
>  	writel_relaxed(GICD_CTLR_ARE_NS | GICD_CTLR_ENABLE_G1A |
> GICD_CTLR_ENABLE_G1, base + GICD_CTLR);
> +	gic_dist_wait_for_rwp();
>  
>  	/*
>  	 * Set all global interrupts to the boot CPU only. ARE must be
> @@ -986,14 +987,9 @@ static int gic_set_affinity(struct irq_data *d,
> const struct cpumask *mask_val, 
>  	gic_write_irouter(val, reg);
>  
> -	/*
> -	 * If the interrupt was enabled, enabled it again. Otherwise,
> -	 * just wait for the distributor to have digested our changes.
> -	 */
> +	/* If the interrupt was enabled, enabled it again. */
>  	if (enabled)
>  		gic_unmask_irq(d);
> -	else
> -		gic_dist_wait_for_rwp();

I think you are right in this is not needed here.
But I guess this call belongs further up in this function, after the
gic_mask_irq() call, as this one writes to GICD_ICENABLER. So in case this
IRQ was enabled, we should wait for the distributor to have properly
disabled it, before changing its affinity.

Cheers,
Andre.

>  
>  	irq_data_update_effective_affinity(d, cpumask_of(cpu));
>
Zenghui Yu May 13, 2019, 11:55 a.m. UTC | #2
Hi Andre,

On 2019/5/13 16:37, Andre Przywara wrote:
> On Mon, 13 May 2019 04:15:54 +0000
> Zenghui Yu <yuzenghui@huawei.com> wrote:
> 
> Hi,
> 
>> As per ARM IHI 0069D, GICD_CTLR's RWP field tracks updates to:
>>
>> 	GICD_CTLR's Group Enable bits, for transitions from 1 to 0 only
>> 	GICD_CTLR's ARE bits, E1NWF bit and DS bit (if we have)
>> 	GICD_ICENABLER<n>
>>
>> We seemed use this field in an inappropriate way, somewhere in the
>> GIC-v3 driver. For some examples:
>>
>> In gic_set_affinity(), if the interrupt was not enabled, we only need
>> to write GICD_IROUTER<n> with the appropriate mpidr value. Updates to
>> GICD_IROUTER will not be tracked by RWP field, and we can remove the
>> unnecessary RWP waiting.
> 
> I am not sure this is the proper fix, see below inline.
> 
>> In gic_dist_init(), we "Enable distributor with ARE, Group1" by writing
>> to GICD_CTLR, and we should use gic_dist_wait_for_rwp() here.
> 
> That looks reasonable, yes.
> 
>> These two are obvious cases, and there are some other cases where we don't
>> need to do RWP waiting, such as in gic_configure_irq() and gic_poke_irq().
>> But too many modifications makes me not confident. It's hard for me to say
>> whether this patch is doing the right thing and how does the RWP waiting
>> affect the system, thus RFC.
> 
> So did you actually see a problem, and this patch fixes it? Or was this
> just discovered by code inspection and comparing to the spec?

The latter ;-)

>> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
>> ---
>>   drivers/irqchip/irq-gic-v3.c | 8 ++------
>>   1 file changed, 2 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
>> index 15e55d3..8d63950 100644
>> --- a/drivers/irqchip/irq-gic-v3.c
>> +++ b/drivers/irqchip/irq-gic-v3.c
>> @@ -600,6 +600,7 @@ static void __init gic_dist_init(void)
>>   	/* Enable distributor with ARE, Group1 */
>>   	writel_relaxed(GICD_CTLR_ARE_NS | GICD_CTLR_ENABLE_G1A |
>> GICD_CTLR_ENABLE_G1, base + GICD_CTLR);
>> +	gic_dist_wait_for_rwp();
>>   
>>   	/*
>>   	 * Set all global interrupts to the boot CPU only. ARE must be
>> @@ -986,14 +987,9 @@ static int gic_set_affinity(struct irq_data *d,
>> const struct cpumask *mask_val,
>>   	gic_write_irouter(val, reg);
>>   
>> -	/*
>> -	 * If the interrupt was enabled, enabled it again. Otherwise,
>> -	 * just wait for the distributor to have digested our changes.
>> -	 */
>> +	/* If the interrupt was enabled, enabled it again. */
>>   	if (enabled)
>>   		gic_unmask_irq(d);
>> -	else
>> -		gic_dist_wait_for_rwp();
> 
> I think you are right in this is not needed here.
> But I guess this call belongs further up in this function, after the
> gic_mask_irq() call, as this one writes to GICD_ICENABLER. So in case this
> IRQ was enabled, we should wait for the distributor to have properly
> disabled it, before changing its affinity.

I still think we don't need this call in gic_set_affinity().
Actually, the writes to GICD_ICENABLER happens in gic_poke_irq(). And we
already have a gic_dist_wait_for_rwp() there, named rwp_wait().


thanks,
zenghui

> 
> Cheers,
> Andre.
> 
>>   
>>   	irq_data_update_effective_affinity(d, cpumask_of(cpu));
>>   
> 
> 
> .
>

Patch
diff mbox series

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 15e55d3..8d63950 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -600,6 +600,7 @@  static void __init gic_dist_init(void)
 	/* Enable distributor with ARE, Group1 */
 	writel_relaxed(GICD_CTLR_ARE_NS | GICD_CTLR_ENABLE_G1A | GICD_CTLR_ENABLE_G1,
 		       base + GICD_CTLR);
+	gic_dist_wait_for_rwp();
 
 	/*
 	 * Set all global interrupts to the boot CPU only. ARE must be
@@ -986,14 +987,9 @@  static int gic_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
 
 	gic_write_irouter(val, reg);
 
-	/*
-	 * If the interrupt was enabled, enabled it again. Otherwise,
-	 * just wait for the distributor to have digested our changes.
-	 */
+	/* If the interrupt was enabled, enabled it again. */
 	if (enabled)
 		gic_unmask_irq(d);
-	else
-		gic_dist_wait_for_rwp();
 
 	irq_data_update_effective_affinity(d, cpumask_of(cpu));