u-boot/arch/arm/mach-bcm283x/Kconfig
Stephen Warren 79340db7f1 ARM: bcm2835: implement phys_to_bus/bus_to_phys
The BCM283[56] contain both a L1 and L2 cache between the GPU (a/k/a
VideoCore CPU?) and DRAM. DMA-capable peripherals can also optionally
access DRAM via this same  L2 cache (although they always bypass the L1
cache). Peripherals select whether to use or bypass the cache via the
top two bits of the bus address.

An IOMMU exists between the ARM CPU and the rest of the system. This
controls whether the ARM CPU's accesses use or bypass the L1 and/or L2
cache. This IOMMU is configured/controlled exclusively by the VideoCore
CPU.

In order for DRAM accesses made by the ARM core to be coherent with
accesses made by other DMA peripherals, we must program a bus address
into those peripherals that causes the peripheral's accesses to use the
same set of caches that the ARM core's accesses will use.

On the RPi1, the VideoCore firmware sets up the IOMMU to enable use of
the L2 cache. This corresponds to addresses based at 0x40000000.

On the RPi2, the VideoCore firmware sets up the IOMMU to disable use of
the L2 cache. This corresponds to addresses based at 0xc0000000.

This patch implements U-Boot's phys_to_bus/bus_to_phys APIs according
to those rules.

For full details of this setup, please see Dom Cobley's description at:
http://lists.denx.de/pipermail/u-boot/2015-March/208201.html
http://permalink.gmane.org/gmane.comp.boot-loaders.u-boot/215038
https://www.mail-archive.com/u-boot@lists.denx.de/msg166568.html

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00

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menu "Broadcom BCM283X family"
depends on ARCH_BCM283X
choice
prompt "Broadcom BCM283X board select"
config TARGET_RPI
bool "Raspberry Pi"
select CPU_ARM1176
config TARGET_RPI_2
bool "Raspberry Pi 2"
select CPU_V7
endchoice
config DM
default y
config DM_SERIAL
default y
config DM_GPIO
default y
config PHYS_TO_BUS
default y
config SYS_BOARD
default "rpi" if TARGET_RPI
default "rpi_2" if TARGET_RPI_2
config SYS_VENDOR
default "raspberrypi"
config SYS_SOC
default "bcm283x"
config SYS_CONFIG_NAME
default "rpi" if TARGET_RPI
default "rpi_2" if TARGET_RPI_2
endmenu