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

From: Yong Wu
Date: Mon Jan 25 2021 - 02:41:41 EST

On Mon, 2021-01-25 at 13:18 +0900, Tomasz Figa wrote:
> On Wed, Jan 20, 2021 at 4:08 PM Yong Wu <yong.wu@xxxxxxxxxxxx> wrote:
> >
> > On Wed, 2021-01-20 at 13:15 +0900, Tomasz Figa wrote:
> > > On Wed, Jan 13, 2021 at 3:45 PM Yong Wu <yong.wu@xxxxxxxxxxxx> 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@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?
> > > >
> > > > 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.
> >
> > Yes. Each a address spaces is 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.
> >
> > Thanks very much for your review.
> >
>
> Hmm, I had a look at v6 and it still has the address spaces hardcoded
> in the DTS.

sorry. I didn't get here. where do you mean. or help reply in v6.

I only added the preassign list as comment in the file
(dt-binding/memory/mt8192-larb-port.h). I thought our iommu consumer may
need it when they use these ports. they need add dma-ranges property if
its iova is over 4GB.

> Could we move the fixed assignment to the MTK IOMMU driver code instead,
> so that it can be easily adjusted as the kernel code
> evolves without the need to update the DTS?
>
> > >
> > > >
> > > > 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.
> >
> > Sorry for here. I forgot a thing here. that interface above still will
> > not be helpful. If we don't divide the whole 16GB ranges into 4
> > regions(let all the other ranges be dynamical), It won't work since we
> > can only adjust bank_sel with the larb as unit. This is a problem. there
> > are many ports in a larb. Take a example, the address for vcodec read
> > port is 32bits while the address for vcodec write port is 33bit, then it
> > will fail since we only have one bank_sel setting for one larb.
>
> That's exactly why I proposed to have the API operate based on the
> struct device, rather than individual DMA ports. Although I guess the
> CCU case is different, because it's the same larb as the camera.
>
> Anyway, I agree that we don't have to come up with such an API right now.

Thanks for the confirm.

>
> > Thus we
> > have to use current design.
> >
> > >
> > > >
> > > > 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?
> >
> > Oh. In the code (patch [32/33] of v6), I put CCU0/1 in the cam/mdp
> > region which start at 8G since CCU0/1 is a module of camera.
> >
> > >
> > > 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?
> >
> > About the conflict, I use patch [29/33] of v6 for this. I will reserve
> > this special iova region when the full domain(0-4G in this example)
> > initialize.
> >
> > > Should perhaps disp be assigned 12G ~ 16G instead?
> >
> > I think no need put it to 12G-16G, In previous SoC, we have only 4GB
> > ranges for whole MM engines. currently only cam/mdp domain exclude 128M
> > for CCU. it should be something wrong if this is not enough.
> >
>
> Indeed, space is not a problem, but from the security point of view
> it's undesirable. I believe CCU would be running proprietary firmware,
> so it should be isolated as much as possible from other components.

CCU are in the same larb with camera. Thus, it also need locate the same
iova range with camera.

> And, after all, why waste the remaining 4G of address space?
>
> Best regards,
> Tomasz
>
> > >
> > > 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@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]
> > > >
> >
>
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