Re: [PATCH v3 7/9] iommu/arm-smmu-v3: Shrink the cdtab l1_desc array

[Will Deacon <will@kernel.org>]

On Tue, Aug 06, 2024 at 08:31:21PM -0300, Jason Gunthorpe wrote:
> The top of the 2 level CD table is (at most) 1024 entries big, and two
> high order allocations are required. One of __le64 which is programmed
> into the HW (8k) and one of struct arm_smmu_l1_ctx_desc which holds the
> CPU pointer (16k).
> 
> There are two copies of the l2ptr_dma, one is stored in the struct
> arm_smmu_l1_ctx_desc, and another is encoded in the __le64 for the HW to
> use. Instead of storing two copies just decode the value from the __le64.
> 
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 41 +++++++++------------
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  1 -
>  2 files changed, 17 insertions(+), 25 deletions(-)
> 
> 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 e6607d9d590c4d..d23a845ad82223 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -1179,31 +1179,19 @@ static void arm_smmu_sync_cd(struct arm_smmu_master *master,
>  	arm_smmu_cmdq_batch_submit(smmu, &cmds);
>  }
>  
> -static int arm_smmu_alloc_cd_leaf_table(struct arm_smmu_device *smmu,
> -					struct arm_smmu_l1_ctx_desc *l1_desc)
> +static void arm_smmu_write_cd_l1_desc(__le64 *dst, dma_addr_t l2ptr_dma)
>  {
> -	size_t size = CTXDESC_L2_ENTRIES * (CTXDESC_CD_DWORDS << 3);
> -
> -	l1_desc->l2ptr = dma_alloc_coherent(smmu->dev, size,
> -					    &l1_desc->l2ptr_dma, GFP_KERNEL);
> -	if (!l1_desc->l2ptr) {
> -		dev_warn(smmu->dev,
> -			 "failed to allocate context descriptor table\n");
> -		return -ENOMEM;
> -	}
> -	return 0;
> -}
> -
> -static void arm_smmu_write_cd_l1_desc(__le64 *dst,
> -				      struct arm_smmu_l1_ctx_desc *l1_desc)
> -{
> -	u64 val = (l1_desc->l2ptr_dma & CTXDESC_L1_DESC_L2PTR_MASK) |
> -		  CTXDESC_L1_DESC_V;
> +	u64 val = (l2ptr_dma & CTXDESC_L1_DESC_L2PTR_MASK) | CTXDESC_L1_DESC_V;
>  
>  	/* The HW has 64 bit atomicity with stores to the L2 CD table */
>  	WRITE_ONCE(*dst, cpu_to_le64(val));
>  }
>  
> +static dma_addr_t arm_smmu_cd_l1_get_desc(const __le64 *src)
> +{
> +	return le64_to_cpu(*src) & CTXDESC_L1_DESC_L2PTR_MASK;
> +}
> +
>  struct arm_smmu_cd *arm_smmu_get_cd_ptr(struct arm_smmu_master *master,
>  					u32 ssid)
>  {
> @@ -1243,13 +1231,17 @@ static struct arm_smmu_cd *arm_smmu_alloc_cd_ptr(struct arm_smmu_master *master,
>  
>  		l1_desc = &cd_table->l1_desc[idx];
>  		if (!l1_desc->l2ptr) {
> -			__le64 *l1ptr;
> +			dma_addr_t l2ptr_dma;
>  
> -			if (arm_smmu_alloc_cd_leaf_table(smmu, l1_desc))
> +			l1_desc->l2ptr = dma_alloc_coherent(
> +				smmu->dev,
> +				CTXDESC_L2_ENTRIES * sizeof(struct arm_smmu_cd),
> +				&l2ptr_dma, GFP_KERNEL);

Here's another example of the inconsistent indentation.

Will