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> > > > > > > > > > > > nvidia,memory-controller =3D <&mc>; > > > > > > - status =3D "disabled"; > > > > > > + status =3D "okay"; > > > > > > }; > > > > > > > > > > > > smmu: iommu@12000000 { > > > > > > > > > > > > -- > > > > > > 2.51.0 > > > > > > > > > > > > > > > > > > > > > > Question for Jon as the author of the commit being reverted. The > > > > > commit message states "we do not have a way to pass frame-buffer > > > > > memory from the bootloader to the kernel". If I understand this > > > > > correctly, this is talking about seamless handoff. What does this= have > > > > > to do with enabling mmu on the display controllers? Seamless does= not > > > > > work on any tegra arch as far as I'm aware, but Tegra194 is the o= nly > > > > > one that doesn't have mmu enabled for the dc's. But enabling mmu > > > > > allows for better and faster memory allocation. My initial attemp= ts to > > > > > enable this didn't work because I tried to attach them to the mai= n mmu > > > > > unit, see the related freedesktop issue [0]. After noticing in th= e > > > > > downstream dt that the dc's are on a separate unit, I made it wor= k. > > > > > And so far, it seems to work just as well as Tegra186. Then when = I was > > > > > packaging up the change to submit, I found that this had been > > > > > explicitly disabled. But I'm not seeing why. Am I missing some > > > > > additional factors? > > > > > > > > This isn't seamless handoff to the Tegra DRM driver for display, bu= t > > > > rather to simple-framebuffer. While this does technically work, it = also > > > > causes a spew of SMMU faults during early boot because the firmware= does > > > > not properly pass the SMMU mapping information to the kernel. > > > > > > > > In a nutshell what happens is that the firmware sets up the display > > > > controller to scan out from a reserved memory region, but it does s= o > > > > without involving the SMMU, so it uses physical addresses directly.= When > > > > the kernel boots and the SMMU is enabled the continued accesses fro= m > > > > display hardware cause SMMU faults (because there is no mapping for= the > > > > framebuffer addresses). > > > > > > > > That said, we did solve these issues and this may not be happening > > > > anymore with the most recent L4T releases, so it may be okay to rev= ert > > > > this now. We should find out exactly which release includes all the > > > > needed changes so that it can be referenced in the commit message. = I > > > > want to avoid people running new kernels with an old L4T release an= d > > > > then seeing these errors without any reference as to why that might > > > > suddenly happen. > > > > > > For reference, I have rolled back my Android usecase to use the L4T > > > r32.7.6 bootloaders on T194 for a variety of reasons. So I am using > > > cboot as the final bootloader and not edk2 as in L4T r34/r35. I have = a > > > pending cboot patch to support simple-framebuffer handoff, but haven'= t > > > fully verified it as tegra-drm is currently unable to takeover from > > > simplefb like openrm does for t234. But all that to say that since I > > > no longer use r35 for t194 I don't have the setup to easily verify > > > which point release works here and what doesn't. > >=20 > > Any further thoughts on this patch? > >=20 > > Aaron >=20 > FWIW, >=20 > looks like the edk2 patch to update iommu-addresses -- >=20 > commit 6071946461389221d2314cbbae0377610b5b1f6a > Author: Jan Bobek > Date: Tue Mar 21 00:15:27 2023 +0000 >=20 > feat(NvDisplayControllerDxe): update FDT with framebuffer info > =20 > On ready-to-boot and whenever FDT is installed, update FDT with > framebuffer mode information, base address and size. > =20 > Signed-off-by: Jan Bobek > Reviewed-by: Ashish Singhal >=20 > is in since r36.2 >=20 > $ git tag --contains 6071946461389221d2314cbbae0377610b5b1f6a | grep "^r"= =20 > r36.2 > r36.3.0 > r36.4.0 > r36.4.3 > r36.4.4 > r36.4.5 > r38.2 > r38.4 >=20 > Not so good for T194 since r36 only supports Orin. >=20 > I'll look into getting this cherry-picked to r35. >=20 > Mikko >=20 >=20 I looked into this and it appears a version of this is in r35, but it only = supports T234. However, I also found that at one point, L4T bootloader conf= iguration has been modified to place the display controllers into SMMU bypa= ss until otherwise configured by the kernel -- which the kernel does in teg= ra_mc_probe_device. I think that means there is still potential for an issue where the display = continues to be on between tegra_mc_probe_device and tegradrm reconfiguring= it. However, I cannot reproduce that happening -- most likely the display = is being turned off before that because of a clock or power domain being tu= rned off. In any case, this means that we no longer need to pass the framebuffer's in= formation to the kernel. I think it would be good to have some clarity to e= nsure the issue described above cannot happen, but otherwise we should be a= ble to enable IOMMU. Mikko