Re: [PATCH next 2/2] iommu/tegra241-cmdqv: Do not allocate vcmdq until dma_set_mask_and_coherent

On Wed, Sep 04, 2024 at 07:40:43PM -0700, Nicolin Chen wrote:

It's observed that, when the first 4GB of system memory was reserved, all
VCMDQ allocations failed (even with the smallest qsz in the last attempt):
    arm-smmu-v3: found companion CMDQV device: NVDA200C:00
    arm-smmu-v3: option mask 0x10
    arm-smmu-v3: failed to allocate queue (0x8000 bytes) for vcmdq0
    acpi NVDA200C:00: tegra241_cmdqv: Falling back to standard SMMU CMDQ
    arm-smmu-v3: ias 48-bit, oas 48-bit (features 0x001e1fbf)
    arm-smmu-v3: allocated 524288 entries for cmdq
    arm-smmu-v3: allocated 524288 entries for evtq
    arm-smmu-v3: allocated 524288 entries for priq

This is because the 4GB reserved memory shifted the entire DMA zone from a
lower 32-bit range (on a system without the 4GB carveout) to higher range,
while the dev->coherent_dma_mask was set to DMA_BIT_MASK(32) by default.

The dma_set_mask_and_coherent() call is done in arm_smmu_device_hw_probe()
of the SMMU driver. So any DMA allocation from tegra241_cmdqv_probe() must
wait until the coherent_dma_mask is correctly set.

Move the vintf/vcmdq structure initialization routine into a different op,
"init_structures". Call it at the end of arm_smmu_init_structures(), where
standard SMMU queues get allocated.

Most of the impl_ops aren't ready until vintf/vcmdq structure are init-ed.
So replace the full impl_ops with an init_ops in __tegra241_cmdqv_probe().

And switch to tegra241_cmdqv_impl_ops later in arm_smmu_init_structures().
Note that tegra241_cmdqv_impl_ops does not link to the new init_structures
op after this switch, since there is no point in having it once it's done.

Fixes: 918eb5c856f6 ("iommu/arm-smmu-v3: Add in-kernel support for NVIDIA Tegra241 (Grace) CMDQV")
Reported-by: Matt Ochs <redacted>
Signed-off-by: Nicolin Chen <redacted>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   |  9 +-
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h   |  1 +
 .../iommu/arm/arm-smmu-v3/tegra241-cmdqv.c    | 83 ++++++++++++-------
 3 files changed, 60 insertions(+), 33 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason