Re: [PATCH v4 05/17] xen/arm: ITS: implement hw_irq_controller for LPIs

From: Julien Grall <julien.grall@citrix.com>
To: Vijay Kilari <vijay.kilari@gmail.com>,
	Ian Campbell <ian.campbell@citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Prasun Kapoor <Prasun.Kapoor@caviumnetworks.com>,
	Vijaya Kumar K <vijaya.kumar@caviumnetworks.com>,
	Tim Deegan <tim@xen.org>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	Stefano Stabellini <stefano.stabellini@citrix.com>,
	manish.jaggi@caviumnetworks.com
Subject: Re: [PATCH v4 05/17] xen/arm: ITS: implement hw_irq_controller for LPIs
Date: Sat, 11 Jul 2015 20:08:46 +0200	[thread overview]
Message-ID: <55A15BAE.6060100@citrix.com> (raw)
In-Reply-To: <CALicx6tqMkX4Yn8ua=c6q9okT1Srz+5zsto8jkt_MGuiumt-kg@mail.gmail.com>

Hi Vijay,

On 11/07/2015 16:40, Vijay Kilari wrote:
>>> diff --git a/xen/include/asm-arm/gic.h b/xen/include/asm-arm/gic.h
>>> index e9d5f36..44c2317 100644
>>> --- a/xen/include/asm-arm/gic.h
>>> +++ b/xen/include/asm-arm/gic.h
>>> @@ -20,6 +20,9 @@
>>>
>>>   #define NR_GIC_LOCAL_IRQS  NR_LOCAL_IRQS
>>>   #define NR_GIC_SGI         16
>>> +#define FIRST_GIC_LPI      8192
>>> +#define NR_GIC_LPI         4096
>>> +#define MAX_LPI            (FIRST_GIC_LPI + NR_GIC_LPI)
>>
>> MAX_LPI and NR_GIC_LPI should be obtained from the hardware at init time
>> and put somewhere, like a global nr_lpis perhaps, to be used throughout.
>
>   This MAX_LPI and NR_GIC_LPI is Xen limitation where in we
> are allocating irq_descriptors statically upto NR_GIC_LPI.

Why? The design doc [1] suggested to allocate dynamically the irq_desc 
array for LPI at boot.

Using a static array will grow up the Xen binary by close to 4096 LPIs * 
60 bytes (rough estimate) = 240 KB.

And this is for any AArch64 platform, no matter that ITS is in used or not.

Regards,

[1] http://xenbits.xen.org/people/ianc/vits/draftG.html#irq-descriptors

-- 
Julien Grall