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

[Miao Yan]

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.



>
>> +
>> +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 ?


>
>> +    -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