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Re: [Qemu-devel] [PATCH 02/10] pxa2xx_pic: update to use qdev and arm-pi

From: andrzej zaborowski
Subject: Re: [Qemu-devel] [PATCH 02/10] pxa2xx_pic: update to use qdev and arm-pic
Date: Thu, 3 Mar 2011 15:35:32 +0100

On 25 February 2011 14:50, Dmitry Eremin-Solenikov <address@hidden> wrote:
> On 2/25/11, andrzej zaborowski <address@hidden> wrote:
>> Hi Dmitry,
>> On 20 February 2011 14:50, Dmitry Eremin-Solenikov <address@hidden>
>> wrote:
>>> Use qdev/sysbus framework to handle pxa2xx-pic. Instead of exposing IRQs
>>> via array, reference them via qdev_get_gpio_in(). Also pxa2xx_pic
>>> duplicated
>>> some code from arm-pic. Drop it, replacing with references to arm-pic,
>>> as all other ARM SoCs do for their PIC code.
>> As I said earlier not using arm-pic was deliberate (and I also asked
>> what the gain was from converting the pic to a separate sysbus device
>> from the CPU) so I skipped this part of the patch and pushed the rest
>> of it, please check that everything works.
> The primary goal was using arm-pic IRQs in pxa2xx-gpio and not having to
> mess with passing CPUEnv around. Moreover all other ARM SoCs use
> arm-pic w/o any references to performance gains/loses.
> I can still provide a patch that will use arm-pic only for
> pxa2xx-gpio, will that
> be suitable for you?

Well my take on it is that it adds an additional level indirection.
More levels of indirection / abstraction are only good if they enable
some new feature or make a big difference in the code and it's not the
case here.  Otherwise they make bloat and more levels of function
calls which add up to small overheads.  And I don't see using CPUEnv
as a hack anyway.

I pushed the remaining patches with small adjustments.


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