On Fri, 4 Nov 2016 00:17:00 +0800
Xiao Guangrong <guangrong.x...@linux.intel.com> wrote:
>
>
> On 11/04/2016 12:13 AM, Igor Mammedov wrote:
> > On Thu, 3 Nov 2016 22:53:43 +0800
> > Xiao Guangrong <guangrong.x...@linux.intel.com> wrote:
> >
> >>
> >>
> >> On 11/03/2016 10:49 PM, Igor Mammedov wrote:
> >>> On Thu, 3 Nov 2016 21:02:22 +0800
> >>> Xiao Guangrong <guangrong.x...@linux.intel.com> wrote:
> >>>
> >>>>
> >>>>
> >>>> On 11/03/2016 09:00 PM, Igor Mammedov wrote:
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>>>> just drop this and describe properly 'len' in spec section
> >>>>>>> i.e. len: length of entire returned data (including the
> >>>>>>> header)
> >>>>>>
> >>>>>> Okay, i will change the spec like this:
> >>>>>>
> >>>>>> QEMU Writes Output Data (based on the offset in the page):
> >>>>>> [0x0 - 0x3]: 4 bytes, length of entire returned data
> >>>>>> (including the header)
> >>>>>>
> >>>>>> And drop the length field in Read_Fit return buffer, doc
> >>>>>> the fit buffer like this:
> >>>>>>
> >>>>>>
> >>>>>> +----------+--------+--------+-------------------------------------------+
> >>>>>> | Field | Length | Offset |
> >>>>>> Description |
> >>>>>> +----------+--------+--------+-------------------------------------------+
> >>>>> you need to add length here, otherwise this table is not correct
> >>>>
> >>>> Ah, so i am confused.
> >>>>
> >>>> struct NvdimmFuncReadFITOut definition is based on the layout of
> >>>> Read_FI output. You suggested to drop the length filed in
> >>>> NvdimmFuncReadFITOut but keep it in the layout, it is not
> >>>> consistent.
> >>>>
> >>>> I missed something?
> >>>
> >>> +struct NvdimmFuncReadFITOut {
> >>> + /* the size of buffer filled by QEMU. */
> >>> + uint32_t len;
> >>> + uint32_t func_ret_status; /* return status code. */
> >>> + uint8_t fit[0]; /* the FIT data. */
> >>> +} QEMU_PACKED;
> >>>
> >>> --------------------------------
> >>> | field | len | off | desc...
> >>> --------------------------------
> >>> | length | 4 | 0 | ....
> >>> --------------------------------
> >>> | status | 4 | 4 | ....
> >>> --------------------------------
> >>> | fit data | ................
> >>>
> >>> i.e. you were forgetting to add length in spec so offsets were
> >>> wrong even for described fields.
> >>
> >>
> >> We can not do this.
> >>
> >> @len is used by QEMU emulation to count the size of the buffer that
> >> _DSM should return. It's only used in NVDIMM_COMMON_DSM method
> >> which is shared by the DSM method from VM and Read_Fit.
> > spec describes buffer layout independently from AML that uses it,
> > so it should describe whole data structure.
> >
> > Then it's upto guest how to read this data, it could be QEMU
> > generated AML (as it's here) or some other driver or even BIOS.
>
> However, what we are talking about is Read_FIT method, so this is
> the layout of Read_FIT output rather than all memory in the dsm page.
>
> Actually, in the spec we already have documented the common len field:
>
> QEMU Writes Output Data (based on the offset in the page):
> [0x0 - 0x3]: 4 bytes, the length of result
> [0x4 - 0xFFF]: 4092 bytes, the DSM result filled by QEMU
>
> Also, i really do not hope to use this field to count the buffer size
> returned by Read_FIT, we'd try the best to reuse existing DSM method
> (NVDIMM_COMMON_DSM), i.e, treat Read_FIT as normal DSM method.
buffer layout describes interface between QEMU and firmware (AML)
and it should describe it completely every time to avoid confusion.
See for example ACPI spec, NFIT table, SRAT table, ...
all table descriptions start with complete header.
If you skip length it rises question how much fit data are there,
meaning interface description isn't complete.
if you want to describe AML there you can do it after interface
description saying that common NCAL method extracts status and fit
data form dsm page and returns that as buffer object, but it's AML
impl. specific. I could write an alternative AML code that would deal
with dms page in its own way as long as I would know what write/read at
what offset.
>
>
>
>
>
