Re: [Qemu-devel] [PATCH v2] arm: add fw_cfg to "virt" board

[Christopher Covington <cov@codeaurora.org>]

Hi Laszlo,

On 12/08/2014 09:01 AM, Laszlo Ersek wrote:
> On 11/30/14 17:59, Laszlo Ersek 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.
>>
>> 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 <lersek@redhat.com>
>> ---
>>
>> Notes:
>>     v2:
>>     - use a single mmio region of size 0x1000
>>     - set "compatible" property to "qemu,fw-cfg-mmio"
>>
>>  hw/arm/virt.c | 21 +++++++++++++++++++++
>>  1 file changed, 21 insertions(+)
>>
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index 314e55b..af794ea 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -68,6 +68,7 @@ enum {
>>      VIRT_UART,
>>      VIRT_MMIO,
>>      VIRT_RTC,
>> +    VIRT_FW_CFG,
>>  };
>>  
>>  typedef struct MemMapEntry {
>> @@ -107,6 +108,7 @@ static const MemMapEntry a15memmap[] = {
>>      [VIRT_GIC_CPU] =    { 0x08010000, 0x00010000 },
>>      [VIRT_UART] =       { 0x09000000, 0x00001000 },
>>      [VIRT_RTC] =        { 0x09010000, 0x00001000 },
>> +    [VIRT_FW_CFG] =     { 0x09020000, 0x00001000 },
>>      [VIRT_MMIO] =       { 0x0a000000, 0x00000200 },
>>      /* ...repeating for a total of NUM_VIRTIO_TRANSPORTS, each of that size */
>>      /* 0x10000000 .. 0x40000000 reserved for PCI */
>> @@ -519,6 +521,23 @@ static void create_flash(const VirtBoardInfo *vbi)
>>      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(0, 0, base, base + 2);
>> +
>> +    nodename = g_strdup_printf("/fw-cfg@%" PRIx64, base);
>> +    qemu_fdt_add_subnode(vbi->fdt, nodename);
>> +    qemu_fdt_setprop_string(vbi->fdt, nodename,
>> +                            "compatible", "qemu,fw-cfg-mmio");
>> +    qemu_fdt_setprop_sized_cells(vbi->fdt, nodename, "reg",
>> +                                 2, base, 2, size);
>> +    g_free(nodename);
>> +}
>> +
>>  static void *machvirt_dtb(const struct arm_boot_info *binfo, int *fdt_size)
>>  {
>>      const VirtBoardInfo *board = (const VirtBoardInfo *)binfo;
>> @@ -604,6 +623,8 @@ static void machvirt_init(MachineState *machine)
>>       */
>>      create_virtio_devices(vbi, pic);
>>  
>> +    create_fw_cfg(vbi);
>> +
>>      vbi->bootinfo.ram_size = machine->ram_size;
>>      vbi->bootinfo.kernel_filename = machine->kernel_filename;
>>      vbi->bootinfo.kernel_cmdline = machine->kernel_cmdline;
>>
> 
> So... after playing with this thing for some time, it's become clear
> that "MMIO traps" are painfully slow on the aarch64 platform we've been
> working on (using KVM).
> 
> The original approach in my guest UEFI patch was a simple loop that
> exerted byte-wise access to the fw_cfg device's data register (the only
> kind of access that fw_cfg allows ATM). Downloading a kernel image plus
> an initrd image byte for byte, which together can total between 30MB and
> 50MB, takes simply forever.

Just a thought--would it be possible to add a
DMA-the-whole-thing-to-this-address register to the simulated device?

Chris

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