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Re: [Qemu-devel] [PATCH] raspi: Add Raspberry Pi 1 support

From: Andrew Baumann
Subject: Re: [Qemu-devel] [PATCH] raspi: Add Raspberry Pi 1 support
Date: Mon, 10 Apr 2017 17:08:26 +0000

> From: Andrew Baumann
> Sent: Monday, 10 April 2017 10:05
> > From: Omar Rizwan [mailto:address@hidden
> > Sent: Friday, 7 April 2017 23:13

> > I can't easily find documentation for that 0x40000000 memory mapping,
> > which I figured I'd keep in; should it just be removed from bcm2835?
> > Am I misunderstanding something?
> The various mapping aliases are intended to implement the bus addresses from
> S1.2.3 / figure on page 5 of this document:
> https://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-
> Peripherals.pdf
> In ARM CPU physical addresses, the RAM is mapped at 0, and the peripherals at
> 0x20000000
> In VC CPU bus addresses (which get used for DMA), RAM is aliased four times,
> at 0 0x40000000 0x80000000 and 0xC0000000. Peripherals are also aliased
> four times at a fixed offset of 0x3e000000 from the base of the RAM alias,
> which is how you get the 0x7e000000 peripheral base (0x40000000 +
> 0x3e000000).
> This is implemented as follows: bcm2835_peripherals implements/exports one
> memory region "peri_mr" which contains just the peripherals. It also builds a
> private MR for the GPU ("VC CPU" in the spec) bus addresses, "gpu_mr", and
> aliases RAM into it four times along with the peripheral MR at
> BCM2835_VC_PERI_BASE (0x7e000000). Its parent, device, either bcm2835 or
> bcm2836, maps the peripheral MR into the default sysbus mmio bus (i.e., the
> CPU's physical address space) at the relevant CPU physical base address
> (0x20000000 on pi1, 0x3F000000 on pi2).
> Now, as to why the mapping call fails: I'm confused where you saw that call
> with the 0x40000000 address. The code in my tree for bcm2835.c is:
> /* Peripheral base address seen by the CPU */
> #define BCM2835_PERI_BASE       0x20000000
> ...
>     sysbus_mmio_map_overlap(SYS_BUS_DEVICE(&s->peripherals), 0,
>                             BCM2835_PERI_BASE, 1);

Ok, I just looked at your patch, and it looks like you added the 0x40000000 
mapping. It's definitely not in my tree 
(https://github.com/0xabu/qemu/blob/raspi/hw/arm/bcm2835.c). I would suggest 
taking it back out again and sanity-checking your patch against the code in my 
tree for any other spurious changes that may have snuck in...


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