linux-kernel - Re: [PATCH 1/2] iommu/arm-smmu-v3: Match Stall behaviour for S2

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Message-ID: <20240813170130.GM1985367@ziepe.ca>
Date: Tue, 13 Aug 2024 14:01:30 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mostafa Saleh <smostafa@...gle.com>
Cc: linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, will@...nel.org,
	robin.murphy@....com, joro@...tes.org, nicolinc@...dia.com,
	mshavit@...gle.com
Subject: Re: [PATCH 1/2] iommu/arm-smmu-v3: Match Stall behaviour for S2

On Mon, Aug 12, 2024 at 08:52:54PM +0000, Mostafa Saleh wrote:
> S2S must be set when stall model is forced "ARM_SMMU_FEAT_STALL_FORCE".
> But at the moment the driver ignores that, instead of doing the minimum
> and only set S2S for “ARM_SMMU_FEAT_STALL_FORCE” we can just match what
> S1 does which also set it for “ARM_SMMU_FEAT_STALL” and the master
> has requested stalls.
> This makes the driver more consistent when running on different SMMU
> instances with different supported stages.
> 
> Signed-off-by: Mostafa Saleh <smostafa@...gle.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 5 +++++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index a31460f9f3d4..8d573d9ca93c 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -1562,6 +1562,11 @@ void arm_smmu_make_cdtable_ste(struct arm_smmu_ste *target,
>  		(cd_table->cdtab_dma & STRTAB_STE_0_S1CTXPTR_MASK) |
>  		FIELD_PREP(STRTAB_STE_0_S1CDMAX, cd_table->s1cdmax));
>  
> +	/* S2S is ignored if stage-2 exists but not enabled. */
> +	if (master->stall_enabled &&
> +	    smmu->features & ARM_SMMU_FEAT_TRANS_S2)
> +		target->data[0] |= FIELD_PREP(STRTAB_STE_2_S2S, 1);

The style semes to be to just use

target->data[] |= STRTAB_xx

For single bit, not FIELD_PREP, even though it does work.

And as Robin noted it is data[2], the naming is supposed to make that
apparent with _2_ indicating the word.. But it is quite easy to make
this typo.

Jason