Re: [Xen-devel] [PATCH v3 09/10] arm: add QEMU, Rcar3 and MPSoC configs

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 23/05/18 01:25, Stefano Stabellini wrote:
> Add a "Platform Support" menu with three umbrella kconfig options: QEMU,
> RCAR3 and MPSOC. They enable the required options for their hardware
> platform.
>
> They are introduced for convience: the user will be able to simply open
> the menu and enable the right config for her platform.
>
> Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: artem_mygaiev@xxxxxxxx
> CC: volodymyr_babchuk@xxxxxxxx
>
> ---
> Note that this approach has a limitation: it is not possible to "select
> a range". In other words, using tiny.config NR_CPUS is set to 4. It is
> not possible to increase it to 8 from config RCAR3.
What you can do is:

config NR_CPUS
        range ...
        default "8" if (RCAR3)
        default "x" if (QEMU)
        default 64

This would imply to move NR_CPUS in arch/{arm,x86}/Kconfig.

This solution is not very nice, but at least would provide a better 
experience to the user.
> Suggestions are welcome.
> ---
>   xen/arch/arm/Kconfig           |  2 ++
>   xen/arch/arm/platforms/Kconfig | 30 ++++++++++++++++++++++++++++++
>   2 files changed, 32 insertions(+)
>   create mode 100644 xen/arch/arm/platforms/Kconfig
>
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index a5a6943..b5ddd12 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -245,6 +245,8 @@ config ARM64_HARDEN_BRANCH_PREDICTOR
>   config ARM32_HARDEN_BRANCH_PREDICTOR
>       def_bool y if ARM_32 && HARDEN_BRANCH_PREDICTOR
>   
> +source "arch/arm/platforms/Kconfig"
> +
>   source "common/Kconfig"
>   
>   source "drivers/Kconfig"
> diff --git a/xen/arch/arm/platforms/Kconfig b/xen/arch/arm/platforms/Kconfig
> new file mode 100644
> index 0000000..0eafbef
> --- /dev/null
> +++ b/xen/arch/arm/platforms/Kconfig
> @@ -0,0 +1,30 @@
> +menu "Platform Support"
> +
> +config QEMU
> +       bool "QEMU aarch virt machine support"
> +       default n
The default value is confusing here. The default .config will support 
QEMU but not select that.
While I don't yet buy the argument, some users will also want to remove 
platform specific code (Andrii suggest that). This would means by 
default support for a specific platform will not be in Xen.
Furthermore, very likely, the end user will select either one board (e.g 
automotive) or all of them (e.g distribution).
So I think it would be better to do a choice list:
        - All -> Board support for all board added. Drivers selected by the user
        - MPSOC -> Select board support for Xilinx + appropriate drivers
        - RCAR3 -> Select board support for RCAR3 + appropriate drivers

The tiny.config would select ALL. This could then be refined by 
selecting a specific platform.
Cheers,

--
Julien Grall

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