Re: [Xen-devel] [PATCH V3 8/8] iommu/arm: Add Renesas IPMMU-VMSA support

[Oleksandr <olekstysh@xxxxxxxxx>]

On 29.08.19 11:37, Yoshihiro Shimoda wrote:
> Hi Oleksandr-san,
Hi Shimoda-san.


> > From: Oleksandr Tyshchenko, Sent: Wednesday, August 21, 2019 3:10 AM
> >
> > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> >
> > The IPMMU-VMSA is VMSA-compatible I/O Memory Management Unit (IOMMU)
> > which provides address translation and access protection functionalities
> > to processing units and interconnect networks.
> >
> > Please note, current driver is supposed to work only with newest
> > Gen3 SoCs revisions which IPMMU hardware supports stage 2 translation
> This is still "Gen3", so that please replace it with "R-Car Gen3"...
Will do.


> > table format and is able to use CPU's P2M table as is if one is
> > 3-level page table (up to 40 bit IPA).
> >
> > The major differences compare to the Linux driver are:
> >
> > 1. Stage 1/Stage 2 translation. Linux driver supports Stage 1
> > translation only (with Stage 1 translation table format). It manages
> > page table by itself. But Xen driver supports Stage 2 translation
> > (with Stage 2 translation table format) to be able to share the P2M
> > with the CPU. Stage 1 translation is always bypassed in Xen driver.
> >
> > So, Xen driver is supposed to be used with newest R-Car Gen3 SoC revisions
> > only (H3 ES3.0, M3-W+, etc.) which IPMMU H/W supports stage 2 translation
> > table format.
> >
> > 2. AArch64 support. Linux driver uses VMSAv8-32 mode, while Xen driver
> > enables Armv8 VMSAv8-64 mode to cover up to 40 bit input address.
> >
> > 3. Context bank (sets of page table) usage. In Xen, each context bank is
> > mapped to one Xen domain. So, all devices being pass throughed to the
> > same Xen domain share the same context bank.
> >
> > 4. IPMMU device tracking. In Xen, all IOMMU devices are managed
> > by single driver instance. So, driver uses global list to keep track
> > of registered IPMMU devices.
> >
> > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> > CC: Julien Grall <julien.grall@xxxxxxx>
> > CC: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> About this hardware handling, this patch seems good to me. But, since
> I'm not familiar about Xen passthrough framework, I think I cannot
> add my Reviewed-by tag into this patch. What do you think?
I am not completely sure regarding that, but I have seen cases when the 
people give their R-b not for the entire patch, but for a part of it.
Especially, when patch touches many sub-systems/archs. Would you mind if 
I specify what your R-b covers? -> [for the IPMMU H/W bits]

Thank you for the review.

> Best regards,
> Yoshihiro Shimoda
--
Regards,

Oleksandr Tyshchenko


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