Re: Seeing conflict with IPMMU driver under ACPI

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Ananth,

On Tuesday, 19 September 2017 09:54:49 EEST Jasty, Ananth wrote:
> On Sep 18, 2017, at 11:49 PM, Laurent Pinchart wrote:
> > On Tuesday, 19 September 2017 03:43:05 EEST Jasty, Ananth wrote:
> >> Hi, with your IPMMU driver enabled under 4.13 we’re seeing a crash on
> >> boot:
> >> 
> >> [ 13.785164] Unable to handle kernel NULL pointer dereference at virtual
> >> address 00000018
> >> [ 13.793254] [0000000000000018] user address but active_mm is swapper
> >> [ 13.799600] Internal error: Oops: 96000004 [#1] SMP
> >> [ 13.804466] Modules linked in: aes_neon_bs aes_neon_blk crypto_simd
> >> cryptd
> >> [ 13.811334] CPU: 152 PID: 1529 Comm: kworker/152:1 Not tainted
> >> 4.13.0-9-generic #10-Ubuntu
> >> [ 13.819584] Hardware name: Default string Cavium ThunderX2/Default
> >> string, BIOS 5.13 07/20/2017
> >> [ 13.828285] Workqueue: events deferred_probe_work_func
> >> [ 13.833410] task: ffff80bee93d0000 task.stack: ffff80bee93dc000
> >> [ 13.839330] PC is at iommu_ops_from_fwnode+0x4c/0x90
> >> [ 13.844282] LR is at iommu_ops_from_fwnode+0x28/0x90
> >> 
> >> The ARM SMMUv3 driver (which our platform implements) seems to be losing
> >> iommu_ops to the IPMMU driver.
> > 
> > You seem not to be the first one to notice:
> > 
> > https://patchwork.kernel.org/patch/9956449/\0
> 
> Wow, he did not beat me by much.
> 
> >> Note: our platform uses ACPI for device enumeration.
> >> 
> >> I have no way to test this, but is there a reason the set_iommu isn’t in
> >> _probe?
> > 
> > I can't recall what the reason was I'm afraid.
> 
> arm-smmu-v3.c does do the set_iommu in probe, and thus far there have been
> no confirmed fatalities, but I can't speak authoritatively.
> 
> I'll leave you all to it then.

After digging a bit I realized that calling bus_set_iommu() from the init 
function is needed to support ARM32 (the same driver supports both ARM32 and 
ARM64). Let's discuss the matter in a reply to https://patchwork.kernel.org/
patch/9956449/\0.

-- 
Regards,

Laurent Pinchart