Re: [Qemu-devel] [PATCH v4 04/11] ARM: exynos4210: IRQ subsystem support.

[Evgeny Voevodin <e.voevodin@samsung.com>]

On 12/22/2011 12:31 AM, Peter Maydell wrote:
> On 21 December 2011 15:08, Evgeny Voevodin<e.voevodin@samsung.com>  wrote:
>> On 12/21/2011 05:50 PM, Peter Maydell wrote:
>>> arm_gic.c exposes the CPU and distributor interfaces as their own
>>> memory regions now -- you shouldn't need any of this intermediate
>>> layer of functions.
>> These functions are not actually for splitting CPU and Distributer
>> interfaces.
>> In our board we have two GICs - internal and external. Internal GIC is
>> completely
>> matching arm_gic.c.
>>
>> Internal GIC CPU[n] and Distributer[n] interfaces are at 0x100 and 0x1000
>> offsets from
>> 0x10500000 base.
>>
>> But external GIC is different.
>> It's CPU[0] interface is at 0x0 offset from 0x10480000 base
>> and
>>       CPU[1] interface is at 0x8000 offset from 0x10480000 base
>>
>> It's Distributer[0] interface is at 0x0 offset from 0x10490000 base
>> and
>>       Distributer[1] interface is at 0x8000 offset from 0x10490000 base
>>
>> [n] - is corresponding to SMP CPU Core.
>>
>> So, we need these wrapper functions for External GIC.
> I don't understand this reasoning. If there are two GICs then
> you should just instantiate two GIC devices and map and/or alias
> their memory regions at the right addresses. The reason why
> the distributor and CPU interfaces are exposed as multiple
> memory regions is exactly so you can put them at different
> offsets for different boards/CPUs. If arm_gic doesn't
> provide suitably split up memory regions then it should be
> fixed to do so.
>
> -- PMM
>
One of our GICs (internal) plus private memory region is represented
as "a9mpcore_priv" device. This implementation fits the documentation.

Second GIC (external) is represented as "exynos4210.gic" with splitted
mapping for CPU (0x10480000) and Distributer (0x10490000) (we used
arm_gic.c availability to split CPU and Distributer memories).

The reason for creation of this device with it's own read/write 
functions is:

CPU and Distributer registers which are banked per SMP Core in internal GIC
are not banked in external GIC and their offsets could not be used as is 
with
arm_gic.c.
External GIC registers in comparison to Internal GIC registers are moved
from base by offset n * 0x8000 for each SMP Core, where n is SMP Core index.
The rest functionality of external GIC is identical to internal GIC and 
arm_gic.c.
So, we can use arm_gic.c in external GIC if we will pass correct offsets 
to it's
read/write functions. To obtain arm_gic.c compliant addresses, we introduced
exynos4210_gic/dist_read/write functions. They obtain arm_gic.c compliant
offsets for primary and secondary SMP Cores and simply call arm_gic.c
functions to do all the work.

-- 
Kind regards,
Evgeny Voevodin,
Leading Software Engineer,
ASWG, Moscow R&D center, Samsung Electronics
e-mail: e.voevodin@samsung.com