Re: [Qemu-devel] [qemu PATCH 2/2] arm: add fw_cfg to "virt" board

[Laszlo Ersek <lersek@redhat.com>]

On 11/28/14 11:38, Andrew Jones wrote:
> On Fri, Nov 28, 2014 at 12:18:27AM +0100, 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.
>>
>> 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>
>> ---
>>  hw/arm/virt.c | 21 +++++++++++++++++++++
>>  1 file changed, 21 insertions(+)
>>
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index 314e55b..070bd34 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, FW_CFG_SIZE + FW_CFG_DATA_SIZE },
>>      [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;
>> +    char *nodename;
>> +
>> +    fw_cfg_init(0, 0, base, base + FW_CFG_SIZE);
>> +
>> +    nodename = g_strdup_printf("/fw-cfg@%" PRIx64, base);
>> +    qemu_fdt_add_subnode(vbi->fdt, nodename);
>> +    qemu_fdt_setprop_string(vbi->fdt, nodename,
>> +                            "compatible", "fw-cfg,mmio");
>> +    qemu_fdt_setprop_sized_cells(vbi->fdt, nodename, "reg",
>> +                                 2, base, 2, FW_CFG_SIZE,
>> +                                 2, base + FW_CFG_SIZE, 2, FW_CFG_DATA_SIZE);
> 
> Overkill suggestion alert, but how about defining something like
> 
> #define FW_CFG_SIZE_ALIGNED \
>     MIN(QEMU_ALIGN_UP(FW_CFG_SIZE, FW_CFG_DATA_SIZE), \
>         QEMU_ALIGN_UP(FW_CFG_SIZE, 4))
> 
> and then using that in your memmap size calculation and fw-cfg-data base
> address calculation. The only reason I suggest this is because it's hard
> to tell that fw-cfg-data's address will be naturally aligned without
> hunting down the definition of FW_CFG_DATA_SIZE. And, if it were to change
> (which it probably never will), then it may not be.

Why does it need to be aligned?

The selector register is aligned at a 64KB boundary (for independent,
strict reasons).

The data register is not aligned at all, and -- AFAICS -- it need not
be, because it's 1 byte wide. (In fact the ARM-specific
Mmio(Read|Write)XX functions in edk2 enforce natural alignment, and the
above layout passes without problems.)

The full register block is 3 bytes wide. Is that a problem?

Thanks
Laszlo

> 
>> +    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;
>> -- 
>> 1.8.3.1
>>