Re: [PATCH v5 06/27] dt-bindings: mediatek: Add binding for mt8192 IOMMU

[Tomasz Figa]

On Thu, Dec 24, 2020 at 8:35 PM Yong Wu <yong.wu@xxxxxxxxxxxx> wrote:
>
> On Wed, 2020-12-23 at 17:18 +0900, Tomasz Figa wrote:
> > On Wed, Dec 09, 2020 at 04:00:41PM +0800, Yong Wu wrote:
> > > This patch adds decriptions for mt8192 IOMMU and SMI.
> > >
> > > mt8192 also is MTK IOMMU gen2 which uses ARM Short-Descriptor translation
> > > table format. The M4U-SMI HW diagram is as below:
> > >
> > >                           EMI
> > >                            |
> > >                           M4U
> > >                            |
> > >                       ------------
> > >                        SMI Common
> > >                       ------------
> > >                            |
> > >   +-------+------+------+----------------------+-------+
> > >   |       |      |      |       ......         |       |
> > >   |       |      |      |                      |       |
> > > larb0   larb1  larb2  larb4     ......      larb19   larb20
> > > disp0   disp1   mdp    vdec                   IPE      IPE
> > >
> > > All the connections are HW fixed, SW can NOT adjust it.
> > >
> > > mt8192 M4U support 0~16GB iova range. we preassign different engines
> > > into different iova ranges:
> > >
> > > domain-id  module     iova-range                  larbs
> > >    0       disp        0 ~ 4G                      larb0/1
> > >    1       vcodec      4G ~ 8G                     larb4/5/7
> > >    2       cam/mdp     8G ~ 12G             larb2/9/11/13/14/16/17/18/19/20
> >
> > Why do we preassign these addresses in DT? Shouldn't it be a user's or
> > integrator's decision to split the 16 GB address range into sub-ranges
> > and define which larbs those sub-ranges are shared with?
>
> The problem is that we can't split the 16GB range with the larb as unit.
> The example is the below ccu0(larb13 port9/10) is a independent
> range(domain), the others ports in larb13 is in another domain.
>
> disp/vcodec/cam/mdp don't have special iova requirement, they could
> access any range. vcodec also can locate 8G~12G. it don't care about
> where its iova locate. here I preassign like this following with our
> internal project setting.

Let me try to understand this a bit more. Given the split you're
proposing, is there actually any isolation enforced between particular
domains? For example, if I program vcodec to with a DMA address from
the 0-4G range, would the IOMMU actually generate a fault, even if
disp had some memory mapped at that address?

>
> Why set this in DT?, this is only for simplifying the code. Assume we
> put it in the platform data. We have up to 32 larbs, each larb has up to
> 32 ports, each port may be in different iommu domains. we should have a
> big array for this..however we only use a macro to get the domain in the
> DT method.
>
> When replying this mail, I happen to see there is a "dev->dev_range_map"
> which has "dma-range" information, I think I could use this value to get
> which domain the device belong to. then no need put domid in DT. I will
> test this.

My feeling is that the only part that needs to be enforced statically
is the reserved IOVA range for CCUs. The other ranges should be
determined dynamically, although I think I need to understand better
how the hardware and your proposed design work to tell what would be
likely the best choice here.

Best regards,
Tomasz

>
> Thanks.
> >
> > Best regards,
> > Tomasz
> >
> > >    3       CCU0    0x4000_0000 ~ 0x43ff_ffff     larb13: port 9/10
> > >    4       CCU1    0x4400_0000 ~ 0x47ff_ffff     larb14: port 4/5
> > >
> > > The iova range for CCU0/1(camera control unit) is HW requirement.
> > >
> > > Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> > > Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
> > > ---
> > >  .../bindings/iommu/mediatek,iommu.yaml        |  18 +-
> > >  include/dt-bindings/memory/mt8192-larb-port.h | 240 ++++++++++++++++++
> > >  2 files changed, 257 insertions(+), 1 deletion(-)
> > >  create mode 100644 include/dt-bindings/memory/mt8192-larb-port.h
> > >
> [snip]