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

Tomasz Figa
2021-01-20T04:22:14Z

On Wed, Jan 13, 2021 at 3:45 PM Yong Wu <yong.wu@mediatek.com> wrote:
>
> On Wed, 2021-01-13 at 14:30 +0900, Tomasz Figa wrote:
> > On Thu, Dec 24, 2020 at 8:35 PM Yong Wu <yong.wu@mediatek.com> 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?
>
> In this case. we will get fault in current SW setting.
>

Okay, thanks.

> >
> > >
> > > 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.
>
> I have removed the domid patch in v6. and get the domain id in [27/33]
> in v6..
>
> About the other ranges should be dynamical, the commit message [30/33]
> of v6 should be helpful. the problem is that we have a bank_sel setting
> for the iova[32:33]. currently we preassign this value. thus, all the
> ranges are fixed. If you adjust this setting, you can let vcodec access
> 0~4G.

Okay, so it sounds like we effectively have four 4G address spaces and
we can assign the master devices to them. I guess each of these
address spaces makes for an IOMMU group.

It's fine to pre-assign the devices to those groups for now, but it
definitely shouldn't be hardcoded in DT, because it depends on the use
case of the device. I'll take a look at v6, but it sounds like it
should be fine if it doesn't take the address space assignment from DT
anymore.

>
> Currently we have no interface to adjust this setting. Suppose we add a
> new interface for this. It would be something like:
>
> int mtk_smi_larb_config_banksel(struct device *larb, int banksel)
>
> Then, all the MM drivers should call it before the HW works every
> time, and its implement will be a bit complex since we aren't sure if
> the larb has power at that time. the important thing is that the MM
> devices have already not known which larb it connects with as we plan to
> delete "mediatek,larb" in their dtsi nodes.

From the practical point of view, it doesn't look like setting this on
a per-larb basis would make much sense. The reason to switch the
bank_sel would be to decide which MM devices can share the same
address space. This is a security aspect, because it effectively
determines which devices are isolated from each other.

That said, I agree that for now we can just start with a fixed
assignment. We can think of the API if there is a need to adjust the
assignment.

>
> In current design, the MM device don't need care about it and 4GB
> range is enough for them.
>

Actually, is the current assignment correct?

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
3 CCU0 0x4000_0000 ~ 0x43ff_ffff larb13: port 9/10
4 CCU1 0x4400_0000 ~ 0x47ff_ffff larb14: port 4/5

Wouldn't CCU0 and CCU1 conflict with disp? Should perhaps disp be
assigned 12G ~ 16G instead?

Best regards,
Tomasz

> >
> > 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@mediatek.com>
> > > > > Reviewed-by: Rob Herring <robh@kernel.org>
> > > > > ---
> > > > > .../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]
>