arm: add fw_cfg to "virt" board
fw_cfg already supports exposure over MMIO (used in ppc/mac_newworld.c, ppc/mac_oldworld.c, sparc/sun4m.c); we can easily add it to the "virt" board. Because MMIO access is slow on ARM KVM, we enable the guest, with fw_cfg_init_mem_wide(), to transfer up to 8 bytes with a single access. This has been measured to speed up transfers up to 7.5-fold, relative to single byte data access, on both ARM KVM and x86_64 TCG. The MMIO register block of fw_cfg is advertized in the device tree. As base address we pick 0x09020000, which conforms to the comment preceding "a15memmap": it falls in the miscellaneous device I/O range 128MB..256MB, and it is aligned at 64KB. The DTB properties follow the documentation in the Linux source file "Documentation/devicetree/bindings/arm/fw-cfg.txt". fw_cfg automatically exports a number of files to the guest; for example, "bootorder" (see fw_cfg_machine_reset()). Signed-off-by: NLaszlo Ersek <lersek@redhat.com> Reviewed-by: NPeter Maydell <peter.maydell@linaro.org> Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com> Message-id: 1419250305-31062-9-git-send-email-pbonzini@redhat.com Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
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