[U-Boot] [PATCH 7/7] qemu-x86: add documentaion for the fw_cfg interface

[Bin Meng]

Hi Miao,

On Tue, Dec 29, 2015 at 2:47 PM, Miao Yan <yanmiaobest at gmail.com> wrote:
> Hi Bin,
>
> 2015-12-29 14:19 GMT+08:00 Bin Meng <bmeng.cn at gmail.com>:
>> Hi Miao,
>>
>> nits: please use "x86: qemu" as the tag in the commit title.
>>
>> On Mon, Dec 28, 2015 at 5:18 PM, Miao Yan <yanmiaobest at gmail.com> wrote:
>>> Document the usage of 'fw' command
>>>
>>> Signed-off-by: Miao Yan <yanmiaobest at gmail.com>
>>> ---
>>>  doc/README.x86 | 36 +++++++++++++++++++++++++++++++++---
>>>  1 file changed, 33 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/doc/README.x86 b/doc/README.x86
>>> index 1271e5e..f39c157 100644
>>> --- a/doc/README.x86
>>> +++ b/doc/README.x86
>>> @@ -295,9 +295,39 @@ show QEMU's VGA console window. Note this will disable QEMU's serial output.
>>>  If you want to check both consoles, use '-serial stdio'.
>>>
>>>  Multicore is also supported by QEMU via '-smp n' where n is the number of cores
>>> -to instantiate. Currently the default U-Boot built for QEMU supports 2 cores.
>>> -In order to support more cores, you need add additional cpu nodes in the device
>>> -tree and change CONFIG_MAX_CPUS accordingly.
>>> +to instantiate. U-Boot uses fw_cfg interface provided by QEMU to detect certain
>>> +system information, such as cpu number, so 'n' can be any number allowed by
>>> +QEMU.
>>
>> I've tested this. Looks when n > 47, U-Boot mp_init() will fail. I
>> guess we may need limit U-Boot maximum supported cpu number to some
>> reasonable number, say 32?
>
> Did you see this error:
>
>      error adding apic-id: FDT_ERR_NOSPACE (-3)
>
> No spaces left in dtb when there are too many cpus. I guess
> reserve more spaces for dtb should do.  U-Boot itself should
> not limit the cpu number.
>
>

Yes, I see. So we may need fix this fdt size problem if we don't limit
the maximum supported cpu numbers in U-Boot.

>
>>
>>> +
>>> +The fw_cfg interface in QEMU also provides information about kernel data, initrd
>>> +,command-line arguments and more. U-Boot supports directly accessing these informtion
>>> +from fw_cfg interface, this saves the time of loading them from hard disk or
>>> +network again, through emulated devices. To use it , simply providing them in
>>> +QEMU command line:
>>> +
>>> +$ qemu-system-x86_64 -nographic -bios path/to/u-boot.rom -m 1024 -kernel /path/to/bzImage
>>
>> Please use qemu-system-i386 for consistency with other instances
>> mentioned in the doc.
>
> Maybe changing them to qemu-system-x86_64 is better ?

I would like to still use -i386 version because U-Boot is compiled and
run in 32-bit mode only, even if -x86_64 version can run 32-bit
U-Boot.

>
>
>>
>>> +    -append 'root=/dev/sda1 console=ttyS0' -initrd /path/to/initrd -smp 8
>>> +
>>> +Note: -initrd and -smp are both optional
>>> +
>>> +Then start QEMU, in U-Boot command line use the following U-Boot command to setup kernel:
>>> +
>>> + => fw
>>> +fw - qemu firmware interface
>>> +
>>> +Usage:
>>> +fw <command>
>>> +    - list        : print firmware(s) currently loaded
>>> +    - cpus        : print online cpu number
>>> +    - load <addr> : load kernel (if any) to address <addr>
>>> +
>>> +=> fw load
>>> +loading kernel to address 01000000, initrd 015dd010
>>> +
>>> +Here the kernel (bzImage) is loaded to 01000000 and initrd is to 0x15dd010. Then, 'zboot'
>>
>> Looks 01000000 is not kernel (bzImage) address. It is setup data
>> address. Can we enhance the 'fw load' command to output all available
>> loaded components address and size?
>>
>>> +can be used to boot the kernel:
>>> +
>>> +=> zboot 01000000 - 015dd010
>>
>> zboot has 4 parameters, the second parameter is kernel image size,
>> which can be zero. The last one is initrd image size, which should not
>> omitted.
>
> I'll have a try.
>
>
> Miao
>
>
>>
>> My test shows the kernel does not recognize my initramfs.gz, kernel log below:
>>
>> [    4.328688] Unpacking initramfs...
>> [    4.331688] Initramfs unpacking failed: junk in compressed archive
>>
>>>
>>>  CPU Microcode
>>>  -------------
>>> --

Regards,
Bin