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

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Message-ID: <01093474-ECAC-4302-B405-4127269CDAB0@nvidia.com>
Date: Thu, 5 Sep 2024 16:26:02 +0000
From: Matt Ochs <mochs@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
CC: Will Deacon <will@...nel.org>, Thierry Reding <thierry.reding@...il.com>,
	Krishna Reddy <vdumpa@...dia.com>, "robin.murphy@....com"
	<robin.murphy@....com>, "joro@...tes.org" <joro@...tes.org>, Jon Hunter
	<jonathanh@...dia.com>, Jason Gunthorpe <jgg@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH next 2/2] iommu/tegra241-cmdqv: Do not allocate vcmdq
 until dma_set_mask_and_coherent

> On Sep 4, 2024, at 9:40 PM, Nicolin Chen <nicolinc@...dia.com> 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 <mochs@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> —

Tested-by: Matt Ochs <mochs@...dia.com>