Re: [Xen-devel] [PATCH] arm64:renesas: Introduce early console for Salvator-X board

[Julien Grall <julien.grall@xxxxxxx>]

On 23/11/16 14:00, Iurii Mykhalskyi wrote:
> Dear all,
Hello Iurii,

> Julien, I have updated yocto layer [1] to use the most recent stable Xen
> version - Xen 4.8-rc6
Can you explain why you want to impose a specific version of Xen to the 
user of this board?
If Xen does not work out-of-box on this box, then you should work 
towards upstreaming the missing pieces.
Also, the way you wrote the page and hook into the main wiki page [6] 
will mislead the user because it gives the impression that you can boot 
xen upstream on the board without any change.
So the wiki page needs to be rewritten to make clear that you are not 
using Xen upstream nor Linux upstream but a custom one maintained by you.
> Looks like used patches for Xen should be described more briefly:
> 1. 0001-arm64-renesas-Introduce-early-console-for-Salvator-X.patch  -
> Early console introduction for Salvator-X board
Patch already posted and will be included in the next version.

> 2. 0002-libxl-Hack-fix-compilation-on-arm64.patch  - required by to fix
> build issue, described here [2]. I haven't found any better solution
> except this one.
Rather than carrying hack on Xen, I would highly recommend you to work 
with the community to fix them upstream. This is a win-win situation for 
everyone.
> 3. 0003-HACK-Fix-compilation-issues.patch  - is a hack to avoid acpi
> compilation issue on arm64 platform. Looks like Andrii faces same
> problem [3] [4].
We are working with Andrii to fix this.

> 4. 0004-Enable-XSM.patch - enable XSM for arm64 build - this patch is
> not essential, but xsm might be usefull for some use-cases.
You impose the user a specific configuration with option that are not 
necessary. The wiki should compile the minimal way to use Xen on this 
platform, i.e:
        - version of Xen
        - version of Linux
        - DTS used
        - U-boot

If you want to use yocto, then fine. But you have to explain what is
done and how the user can modify it.

> 5. 0005-xen-arm-domain_build-allocate-lowmem-for-dom0-as-muc.patch -
> Salvator-X board has 4GB RAM, but has only 32bit DMA controller - so, if
> Dom0 will be allocated at over 4GB space - DMA operation will fail.
>     According to xen-devel list [5], this patch planned to be included
> in Xen 4.9.
> 6. 0006-Do-no-trap-smc-instructions.patch - Renesas use OP-TEE out of
> box, but by default Xen traps such calls, so we have to allow such actions.
This patch allows all the guests to issue an SMC. Are you aware that you 
open a security hole for any user using your recipes to build Xen?
Regarding the limitation you pointed on the wiki page [7], you can use 
platform specific code (see specific_mapping and blacklist_dev) rather 
hacking the device tree. This is my preferred way and avoid the user to 
have to port the hack when upgrade the kernel if the DT needs some upgrade.
To conclude, it looks like to me that Xen is not yet ready to officially 
support this board.
I will be happy to review any of these patches when they will be sent 
upstream.
Regards,

> [1] https://github.com/qbeeukraine/meta-platform-xen
> <https://github.com/qbeeukraine/meta-platform-xen>
> [2] https://lists.xen.org/archives/html/xen-devel/2015-12/msg00137.html
> <https://lists.xen.org/archives/html/xen-devel/2015-12/msg00137.html>
> [3] https://lists.xen.org/archives/html/xen-devel/2016-11/msg01903.html
> <https://lists.xen.org/archives/html/xen-devel/2016-11/msg01903.html>
> [4] https://lists.xen.org/archives/html/xen-devel/2016-11/msg01930.html
> <https://lists.xen.org/archives/html/xen-devel/2016-11/msg01930.html>
> [5] https://lists.xen.org/archives/html/xen-devel/2016-09/msg02561.html
> <https://lists.xen.org/archives/html/xen-devel/2016-09/msg02561.html>
[6] https://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions
[7] 
https://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions/Salvator-X#Known_limitations
--
Julien Grall

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