Re: [Xen-devel] [PATCH v4 02/27] ARM: GICv3 ITS: initialize host ITS

[Julien Grall <julien.grall@xxxxxxx>]

Hi Andre,

On 04/03/2017 09:28 PM, Andre Przywara wrote:
> Map the registers frame for each host ITS and populate the host ITS
> structure with some parameters describing the size of certain properties
> like the number of bits for device IDs.
> Introduce a command line parameter to limit the number of devices Xen
> should handle. This defaults to the value advertised by hardware.
>
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> ---
>  docs/misc/xen-command-line.markdown |  9 ++++++++
>  xen/arch/arm/gic-v3-its.c           | 38 ++++++++++++++++++++++++++++++++
>  xen/arch/arm/gic-v3.c               |  5 +++++
>  xen/include/asm-arm/gic_v3_its.h    | 44 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 96 insertions(+)
>
> diff --git a/docs/misc/xen-command-line.markdown 
> b/docs/misc/xen-command-line.markdown
> index 9eb85d6..5a90625 100644
> --- a/docs/misc/xen-command-line.markdown
> +++ b/docs/misc/xen-command-line.markdown
> @@ -1172,6 +1172,15 @@ based interrupts. Any higher IRQs will be available for 
> use via PCI MSI.
>  ### maxcpus
>  > `= <integer>`
>
> +### max\_its\_device\_bits
> +> `= <integer>`
> +
> +Specifies the maximum number of devices using MSIs on the ARM GICv3 ITS
> +controller to allocate table entries for. Each table entry uses a hardware
> +specific size, typically 8 or 16 bytes. This value is given as the number
> +of bits required to hold one device ID.
> +Defaults to the machine provided value, which is at most 32 bits.
I will re-explain my point here for convenience. I am not in favor of 
this option because a lambda user will not be able to know the correct 
value without the datasheet or help from the vendor.
If a platform is advertising too much device bits and not able to cope 
then it is should be fixed per-platform.
The rest of this patch looks good to me.

Cheers,

--
Julien Grall

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