Re: [Qemu-devel] [PATCH v3 4/7] arm: add fw_cfg to "virt" board

[Peter Maydell]

On 9 December 2014 at 01:13, Laszlo Ersek <address@hidden> wrote:
> 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_data_memwidth(), 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: Laszlo Ersek <address@hidden>
> ---
>
> Notes:
>     v3:
>     - enable 8-byte wide access to fw_cfg MMIO data port [Drew]
>     - expose the exact size of the fused region in the DTB [Peter]
>     - reorder data register and control register so that we can keep the
>       region contiguous and still conform to alignment requirements [Laszlo]
>
>  hw/arm/virt.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 314e55b..274aaae 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -67,8 +67,9 @@ enum {
>      VIRT_GIC_CPU,
>      VIRT_UART,
>      VIRT_MMIO,
>      VIRT_RTC,
> +    VIRT_FW_CFG,
>  };
>
>  typedef struct MemMapEntry {
>      hwaddr base;
> @@ -106,8 +107,9 @@ static const MemMapEntry a15memmap[] = {
>      [VIRT_GIC_DIST] =   { 0x08000000, 0x00010000 },
>      [VIRT_GIC_CPU] =    { 0x08010000, 0x00010000 },
>      [VIRT_UART] =       { 0x09000000, 0x00001000 },
>      [VIRT_RTC] =        { 0x09010000, 0x00001000 },
> +    [VIRT_FW_CFG] =     { 0x09020000, 0x0000000a },
>      [VIRT_MMIO] =       { 0x0a000000, 0x00000200 },
>      /* ...repeating for a total of NUM_VIRTIO_TRANSPORTS, each of that size 
> */
>      /* 0x10000000 .. 0x40000000 reserved for PCI */
>      [VIRT_MEM] =        { 0x40000000, 30ULL * 1024 * 1024 * 1024 },
> @@ -518,8 +520,25 @@ static void create_flash(const VirtBoardInfo *vbi)
>      qemu_fdt_setprop_cell(vbi->fdt, nodename, "bank-width", 4);
>      g_free(nodename);
>  }
>
> +static void create_fw_cfg(const VirtBoardInfo *vbi)
> +{
> +    hwaddr base = vbi->memmap[VIRT_FW_CFG].base;
> +    hwaddr size = vbi->memmap[VIRT_FW_CFG].size;
> +    char *nodename;
> +
> +    fw_cfg_init_data_memwidth(0, 0, base + 8, base, 8);

fw_cfg_init_data_memwidth() adds a bunch of FW_CFG keys
(bootsplash stuff, reboot timeouts, etc). Are you happy that
they all make sense to export on ARM? (I guess we're already doing
that on the other non-x86 fw_cfg users.)

Assuming so,
Reviewed-by: Peter Maydell <address@hidden>

-- PMM