Re: [Qemu-devel] [PATCH v4 28/33] nvdimm acpi: support DSM_FUN_IMPLEMENTED function

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 10/20/2015 11:51 PM, Stefan Hajnoczi wrote:
> On Mon, Oct 19, 2015 at 08:54:14AM +0800, Xiao Guangrong wrote:
>> +exit:
>> +    /* Write our output result to dsm memory. */
>> +    ((dsm_out *)dsm_ram_addr)->len = out->len;
>
> Missing byteswap?
>
> I thought you were going to remove this field because it wasn't needed
> by the guest.
>

The @len is the size of _DSM result buffer, for example, for the function of
DSM_FUN_IMPLEMENTED the result buffer is 8 bytes, and for
DSM_DEV_FUN_NAMESPACE_LABEL_SIZE the buffer size is 4 bytes. It tells ASL code
how much size of memory we need to return to the _DSM caller.

In _DSM code, it's handled like this:

"RLEN" is @len, “OBUF” is the left memory in DSM page.

         /* get @len*/
         aml_append(method, aml_store(aml_name("RLEN"), aml_local(6)));
         /* @len << 3 to get bits. */
         aml_append(method, aml_store(aml_shiftleft(aml_local(6),
                                        aml_int(3)), aml_local(6)));

         /* get @len << 3 bits from OBUF, and return it to the caller. */
         aml_append(method, aml_create_field(aml_name("ODAT"), aml_int(0),
                                             aml_local(6) , "OBUF"));

Since @len is our internally used, it's not return to guest, so i did not do
byteswap here.