Re: [Qemu-devel] [PATCH v4 4/8] bcm2835_peripherals: add rollup device for bcm2835 peripherals

From: Peter Crosthwaite <crosthwaitepeter@gmail.com>
To: Andrew Baumann <Andrew.Baumann@microsoft.com>
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
	"Grégory ESTRADE" <gregory.estrade@gmail.com>,
	"Stefan Weil" <sw@weilnetz.de>,
	"Peter Crosthwaite" <crosthwaite.peter@gmail.com>,
	"qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>,
	qemu-arm <qemu-arm@nongnu.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Rob Herring" <robh@kernel.org>
Subject: Re: [Qemu-devel] [PATCH v4 4/8] bcm2835_peripherals: add rollup device for bcm2835 peripherals
Date: Tue, 26 Jan 2016 00:03:08 -0800	[thread overview]
Message-ID: <CAPokK=rXwURCOc=-W1v+2=Br2kZ4fDXdPUR6gc=UdyoVisY_Bw@mail.gmail.com> (raw)
In-Reply-To: <BLUPR0301MB2034FAE99E63647A00D388E79ED80@BLUPR0301MB2034.namprd03.prod.outlook.com>

On Mon, Jan 25, 2016 at 10:23 PM, Andrew Baumann
<Andrew.Baumann@microsoft.com> wrote:
>> From: Peter Crosthwaite [mailto:crosthwaitepeter@gmail.com]
>> Sent: Monday, 25 January 2016 22:14
>>
>> On Fri, Jan 15, 2016 at 3:58 PM, Andrew Baumann
>> <Andrew.Baumann@microsoft.com> wrote:
> [...]
>> > +static void bcm2835_peripherals_init(Object *obj)
>> > +{
>> > +    BCM2835PeripheralState *s = BCM2835_PERIPHERALS(obj);
>> > +
>> > +    /* Memory region for peripheral devices, which we export to our
>> parent */
>> > +    memory_region_init_io(&s->peri_mr, obj, NULL, s, "bcm2835-
>> peripherals",
>> > +                          0x1000000);
>>
>> Should this just be normal memory_region_init?
>
> I think so -- it's just a container region, and I probably copy and pasted the API here. The two MR init APIs seem almost but not-quite identical when NULL callbacks are used. Can you briefly explain the difference?
>

hmm I guess the defaulting to &unassigned_mem_ops. memory_region_init
looks to assume you will populate the usable subregions. Are you
relying on unassigned ops?

>> > +    object_property_add_child(obj, "peripheral-io", OBJECT(&s->peri_mr),
>> NULL);
>>
>> This seems like a weird parenting, to have the SoC as child to an
>> object it just created. Is the problem you need a parent before others
>> can parent to you?
>
> I'm confused by this question: Unless I'm mistaken, the parent here is BCM2835PeripheralState, the child is the new memory region we just called init on.
>

My bad - I have it backwards.

Regards,
Peter

> Thanks,
> Andrew