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Re: [PATCH] arm/its: enable LPIs before mapping the collection table
- To: Julien Grall <julien@xxxxxxx>
- From: Rahul Singh <Rahul.Singh@xxxxxxx>
- Date: Thu, 28 Apr 2022 10:00:05 +0000
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- Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 28 Apr 2022 10:00:30 +0000
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- Thread-topic: [PATCH] arm/its: enable LPIs before mapping the collection table
Hi Julien,
> On 27 Apr 2022, at 6:59 pm, Julien Grall <julien@xxxxxxx> wrote:
>
> Hi Rahul,
>
> On 27/04/2022 17:14, Rahul Singh wrote:
>> MAPC_LPI_OFF ITS command error can be reported to software if LPIs are
>
> Looking at the spec (ARM IHI 0069H), I can't find a command error named
> MAPC_LPI_OFF. Is it something specific to your HW?
I found the issue on HW that implements GIC-600 and GIC-600 TRM specify the
MAPC_LPI_OFF its command error.
https://developer.arm.com/documentation/100336/0106/introduction/about-the-gic-600
{Table 3-15 ITS command and translation errors, records 13+ page 3-89}
>
>> not enabled before mapping the collection table using MAPC command.
>> Enable the LPIs using GICR_CTLR.EnableLPIs before mapping the collection
>> table.
>> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
>> ---
>> xen/arch/arm/gic-v3.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/xen/arch/arm/gic-v3.c b/xen/arch/arm/gic-v3.c
>> index 3c472ed768..8fb0014b16 100644
>> --- a/xen/arch/arm/gic-v3.c
>> +++ b/xen/arch/arm/gic-v3.c
>> @@ -812,11 +812,11 @@ static int gicv3_cpu_init(void)
>> /* If the host has any ITSes, enable LPIs now. */
>> if ( gicv3_its_host_has_its() )
>> {
>> + if ( !gicv3_enable_lpis() )
>> + return -EBUSY;
>> ret = gicv3_its_setup_collection(smp_processor_id());
>> if ( ret )
>> return ret;
>> - if ( !gicv3_enable_lpis() )
>> - return -EBUSY;
>
> AFAICT, Linux is using the same ordering as your are proposing. It seems to
> have been introduced from the start, so it is not clear why we chose this
> approach.
Yes I also confirmed that before sending the patch for review. I think this is
okay if we enable the enable LPIs before mapping the collection table.
>
> However, given this works on some HW, can you clarify whether this is
> mandated by the spec or this is a bug in your HW?
Regards,
Rahul
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