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From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
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Date: Wed, 21 Oct 2015 00:29:36 +0800
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Subject: Re: [Qemu-devel] [PATCH v4 28/33] nvdimm acpi: support
 DSM_FUN_IMPLEMENTED function
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: ehabkost@redhat.com, kvm@vger.kernel.org, mst@redhat.com, gleb@kernel.org, mtosatti@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, imammedo@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, rth@twiddle.net



On 10/21/2015 12:26 AM, Xiao Guangrong wrote:
>
>
> 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

Sorry, s/DSM_DEV_FUN_NAMESPACE_LABEL_SIZE/DSM_DEV_FUN_SET_NAMESPACE_LABEL_DATA

> 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.