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

[Laszlo Ersek]

On 12/09/14 00:18, Christopher Covington wrote:
> 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 <address@hidden>
>>> ---
>>>
>>> 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("/address@hidden" 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?

That's exactly what Rich proposed in the 2010 thread that I referenced a
few hours ago.

http://thread.gmane.org/gmane.comp.emulators.qemu/77582/focus=77589

(search for '"DMA"-like')

The original patchset is archived at

http://thread.gmane.org/gmane.comp.emulators.qemu/76610/focus=76673

which was shot down; the rebased one got an (unrelated) nack three
months later.

http://thread.gmane.org/gmane.comp.emulators.qemu/77625

Thanks
Laszlo