On 08/12/16 17:06, Oleksandr Tyshchenko wrote:
Hi Julien,
Hi Oleksandr, As discussed on IRC, I CCed xen-devel and Stefano.
We would like to hear your opinion about the proper way of porting kernel driver to XEN. There is a Linux iommu driver "IPMMU VMSA" for supporting VMSA-compatible IPMMUs that are integrated in the newest Renesas SoCs. Mainline: http://lxr.free-electrons.com/source/drivers/iommu/ipmmu-vmsa.c But we would prefer to rely on code that hasn't reach upstream yet but shipped with BSP for this platform and seems to be more complete: https://git.kernel.org/cgit/linux/kernel/git/horms/renesas-bsp.git/tree/drivers/iommu/ipmmu-vmsa.c?h=v4.6/rcar-3.3.x For passthrough and future Remote processor (coproc) use-cases to work on R-Car Gen3 based platforms we need this driver to be ported to XEN. But I am in doubt how to do this in a right way. So, from my point of view there are two possible ways: 1. Try to keep this driver as close as possible from Linux like you did for arm-smmu driver. Even keeping the Linux style. I understand the main goal despite the overhead and so on. 2. Another way is to try to be as similar as possible from arm-smmu driver in XEN. In such case many common for both drivers things might be moved to the common part.
I don't think you would be able to share a lot of code between arm-smmu and ipmmu-vmsa. The former is using stage-2 page table whilst ipmmu-vmsa is using stage-1 page table. So the page table would have to be unshared in your case. This is something we don't yet support on Xen ARM.
Furthermore, I still want to keep arm-smmu as close as possible from Linux mainline. When I first implemented the driver I chose to not stick on Linux, but we decided to re-sync few months later because it was too hard to maintain. One of the main advantage of keeping close to Linux is we can backport bug more easily.
I would prefer to see ipmmu-vmsa as close as Linux (BSP or mainline), but this is not a strong requirement. Do you know why the changes you are looking for are not yet upstreamed? What are the differences?
Cheers, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
