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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 h= ave > > > > to do with enabling mmu on the display controllers? Seamless does n= ot > > > > work on any tegra arch as far as I'm aware, but Tegra194 is the onl= y > > > > one that doesn't have mmu enabled for the dc's. But enabling mmu > > > > allows for better and faster memory allocation. My initial attempts= to > > > > enable this didn't work because I tried to attach them to the main = mmu > > > > unit, see the related freedesktop issue [0]. After noticing in the > > > > downstream dt that the dc's are on a separate unit, I made it work. > > > > 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, but > > > rather to simple-framebuffer. While this does technically work, it al= so > > > causes a spew of SMMU faults during early boot because the firmware d= oes > > > 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 so > > > without involving the SMMU, so it uses physical addresses directly. W= hen > > > the kernel boots and the SMMU is enabled the continued accesses from > > > display hardware cause SMMU faults (because there is no mapping for t= he > > > 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 rever= t > > > 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 and > > > 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 FWIW, looks like the edk2 patch to update iommu-addresses -- commit 6071946461389221d2314cbbae0377610b5b1f6a Author: Jan Bobek Date: Tue Mar 21 00:15:27 2023 +0000 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 is in since r36.2 $ 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 Not so good for T194 since r36 only supports Orin. I'll look into getting this cherry-picked to r35. Mikko