Re: [Qemu-devel] [PATCH v3 3/4] nvdimm acpi: introduce _FIT

[Igor Mammedov <imammedo@redhat.com>]

On Sat, 29 Oct 2016 00:35:39 +0800
Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:

> _FIT is required for hotplug support, guest will inquire the updated
> device info from it if a hotplug event is received
> 
> As FIT buffer is not completely mapped into guest address space, so a
> new function, Read FIT whose UUID is UUID
> 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62, handle 0x10000, function index
> is 0x1, is reserved by QEMU to read the piece of FIT buffer. The buffer
> is concatenated before _FIT return
> 
> Refer to docs/specs/acpi-nvdimm.txt for detailed design
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> ---
>  docs/specs/acpi_nvdimm.txt |  58 ++++++++++++-
>  hw/acpi/nvdimm.c           | 204 ++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 257 insertions(+), 5 deletions(-)
> 
> diff --git a/docs/specs/acpi_nvdimm.txt b/docs/specs/acpi_nvdimm.txt
> index 0fdd251..4aa5e3d 100644
> --- a/docs/specs/acpi_nvdimm.txt
> +++ b/docs/specs/acpi_nvdimm.txt
> @@ -127,6 +127,58 @@ _DSM process diagram:
>   | result from the page     |      |              |
>   +--------------------------+      +--------------+
>  
> - _FIT implementation
> - -------------------
> - TODO (will fill it when nvdimm hotplug is introduced)
> +Device Handle Reservation
> +-------------------------
> +As we mentioned above, byte 0 ~ byte 3 in the DSM memory save NVDIMM device
> +handle. The handle is completely QEMU internal thing, the values in range
> +[0, 0xFFFF] indicate nvdimm device (O means nvdimm root device named NVDR),
> +other values are reserved by other purpose.
> +
> +Current reserved handle:
> +0x10000 is reserved for QEMU internal DSM function called on the root
> +device.
Above part should go to section where 'handle' is defined, i.e. earlier in the file:

   ACPI writes _DSM Input Data (based on the offset in the page):
   [0x0 - 0x3]: 4 bytes, NVDIMM Device Handle, 0 is reserved for NVDIMM
                Root device.


> +QEMU internal use only _DSM function
> +------------------------------------
> +UUID, 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62, is reserved for QEMU internal
> +DSM function.
> +
> +There is the function introduced by QEMU and only used by QEMU internal.
> +
> +1) Read FIT
UUID 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62 is reserved for Read_FIT DSM function
(private QEMU function)

> +   As we only reserved one page for NVDIMM ACPI it is impossible to map the
> +   whole FIT data to guest's address space. This function is used by _FIT
> +   method to read a piece of FIT data from QEMU.
 _FIT method uses Read_FIT function to fetch NFIT structures blob from QEMU
 in 1 page sized increments which are then concatenated and returned as _FIT method result.
 

> +
> +   Input parameters:
> +   Arg0 – UUID {set to 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62}
> +   Arg1 – Revision ID (set to 1)
> +   Arg2 - Function Index, 0x1
> +   Arg3 - A package containing a buffer whose layout is as follows:
> +
> +   +----------+-------------+-------------+-----------------------------------+
> +   |  Filed   | Byte Length | Byte Offset | Description                       |
         ^ field,   s/Byte//,    s/Byte//
> +   +----------+-------------+-------------+-----------------------------------+
> +   | offset   |     4       |    0        | the offset of FIT buffer          |
offset in QEMU's NFIT structures blob to read from

> +   +----------+-------------+-------------+-----------------------------------+
> +
> +   Output:
> +   +----------+-------------+-------------+-----------------------------------+
> +   |  Filed   | Byte Length | Byte Offset | Description                       |
> +   +----------+-------------+-------------+-----------------------------------+
> +   |          |             |             | return status codes               |
> +   |          |             |             |   0x100 indicates fit has been    |
> +   | status   |     4       |    0        |   updated                         |
0x100 - error caused by NFIT update while read by _FIT wasn't completed

> +   |          |             |             | other follows Chapter 3 in DSM    |
s/other follows/other codes follow/

> +   |          |             |             | Spec Rev1                         |
> +   +----------+-------------+-------------+-----------------------------------+
> +   | fit data |  Varies     |    4        | FIT data                          |
> +   |          |             |             |                                   |
> +   +----------+-------------+-------------+-----------------------------------+
what does "Varies" mean, how would I know reading this how much data Read_FIT should read
from shared page?

> +
> +   The FIT offset is maintained by the caller itself,
probably is not necessary sentence, or specify a caller (for example OSPM)

> current offset plugs
                 ^^^^?

> +   the length returned by the function is the next offset we should read.
> +   When all the FIT data has been read out, zero length is returned.
> +
> +   If it returns 0x100, OSPM should restart to read FIT (read from offset 0
> +   again).
[...]
that's all for doc part, I'll do the code part later.