13edcf591e
On the vexpress-a9 board we try to map both RAM and flash to address 0,
as seen in "info mtree":
address-space: memory
0000000000000000-ffffffffffffffff (prio 0, i/o): system
0000000000000000-0000000003ffffff (prio 0, romd): alias vexpress.flashalias @vexpress.flash0 0000000000000000-0000000003ffffff
0000000000000000-0000000003ffffff (prio 0, ram): alias vexpress.lowmem @vexpress.highmem 0000000000000000-0000000003ffffff
0000000010000000-0000000010000fff (prio 0, i/o): arm-sysctl
0000000010004000-0000000010004fff (prio 0, i/o): pl041
(etc)
The flash "wins" and the RAM mapping is useless (but also harmless).
This happened as a result of commit 6ec1588e in 2014, which changed
"we always map the RAM to the low addresses for vexpress-a9" to "we
always map flash in the low addresses", but forgot to stop mapping
the RAM.
In real hardware, this low part of memory is remappable, both at
runtime by the guest writing to a control register, and configurably
as to what you get out of reset -- you can have the first flash
device, or the second, or the DDR2 RAM, or the external AXI bus
(which for QEMU means "nothing there"). In an ideal world we would
support that remapping both at runtime and via a machine property to
select the out-of-reset behaviour.
Pending anybody caring enough to implement the full remapping
behaviour:
* remove the useless mapped-but-inaccessible lowram MR
* document that QEMU doesn't support remapping of low memory
Fixes: 6ec1588e ("hw/arm/vexpress: Alias NOR flash at 0 for vexpress-a9")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1761
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20231103185602.875849-1-peter.maydell@linaro.org
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Arm Versatile Express boards (``vexpress-a9``, ``vexpress-a15``)
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================================================================
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QEMU models two variants of the Arm Versatile Express development
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board family:
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- ``vexpress-a9`` models the combination of the Versatile Express
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motherboard and the CoreTile Express A9x4 daughterboard
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- ``vexpress-a15`` models the combination of the Versatile Express
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motherboard and the CoreTile Express A15x2 daughterboard
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Note that as this hardware does not have PCI, IDE or SCSI,
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the only available storage option is emulated SD card.
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Implemented devices:
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- PL041 audio
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- PL181 SD controller
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- PL050 keyboard and mouse
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- PL011 UARTs
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- SP804 timers
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- I2C controller
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- PL031 RTC
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- PL111 LCD display controller
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- Flash memory
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- LAN9118 ethernet
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Unimplemented devices:
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- SP810 system control block
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- PCI-express
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- USB controller (Philips ISP1761)
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- Local DAP ROM
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- CoreSight interfaces
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- PL301 AXI interconnect
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- SCC
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- System counter
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- HDLCD controller (``vexpress-a15``)
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- SP805 watchdog
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- PL341 dynamic memory controller
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- DMA330 DMA controller
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- PL354 static memory controller
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- BP147 TrustZone Protection Controller
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- TrustZone Address Space Controller
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Other differences between the hardware and the QEMU model:
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- QEMU will default to creating one CPU unless you pass a different
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``-smp`` argument
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- QEMU allows the amount of RAM provided to be specified with the
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``-m`` argument
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- QEMU defaults to providing a CPU which does not provide either
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TrustZone or the Virtualization Extensions: if you want these you
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must enable them with ``-machine secure=on`` and ``-machine
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virtualization=on``
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- QEMU provides 4 virtio-mmio virtio transports; these start at
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address ``0x10013000`` for ``vexpress-a9`` and at ``0x1c130000`` for
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``vexpress-a15``, and have IRQs from 40 upwards. If a dtb is
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provided on the command line then QEMU will edit it to include
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suitable entries describing these transports for the guest.
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- QEMU does not currently support either dynamic or static remapping
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of the area of memory at address 0: it is always mapped to alias
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the first flash bank
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Booting a Linux kernel
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----------------------
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Building a current Linux kernel with ``multi_v7_defconfig`` should be
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enough to get something running. Nowadays an out-of-tree build is
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recommended (and also useful if you build a lot of different targets).
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In the following example $BLD points to the build directory and $SRC
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points to the root of the Linux source tree. You can drop $SRC if you
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are running from there.
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.. code-block:: bash
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$ make O=$BLD -C $SRC ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- multi_v7_defconfig
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$ make O=$BLD -C $SRC ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-
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By default you will want to boot your rootfs off the sdcard interface.
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Your rootfs will need to be padded to the right size. With a suitable
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DTB you could also add devices to the virtio-mmio bus.
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.. code-block:: bash
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$ qemu-system-arm -cpu cortex-a15 -smp 4 -m 4096 \
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-machine type=vexpress-a15 -serial mon:stdio \
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-drive if=sd,driver=file,filename=armel-rootfs.ext4 \
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-kernel zImage \
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-dtb vexpress-v2p-ca15-tc1.dtb \
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-append "console=ttyAMA0 root=/dev/mmcblk0 ro"
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