Re: [RFC PATCH v3 03/12] iommu/io-pgtable: Introduce map_pages() as a page table op

[Will Deacon <will@kernel.org>]

On Mon, Apr 05, 2021 at 12:11:03PM -0700, Isaac J. Manjarres wrote:
> Mapping memory into io-pgtables follows the same semantics
> that unmapping memory used to follow (i.e. a buffer will be
> mapped one page block per call to the io-pgtable code). This
> means that it can be optimized in the same way that unmapping
> memory was, so add a map_pages() callback to the io-pgtable
> ops structure, so that a range of pages of the same size
> can be mapped within the same call.
> 
> Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
> Suggested-by: Will Deacon <will@kernel.org>
> ---
>  include/linux/io-pgtable.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index 2ed0c057d9e7..019149b204b8 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -143,6 +143,7 @@ struct io_pgtable_cfg {
>   * struct io_pgtable_ops - Page table manipulation API for IOMMU drivers.
>   *
>   * @map:          Map a physically contiguous memory region.
> + * @map_pages:    Map a physically contiguous range of pages of the same size.
>   * @unmap:        Unmap a physically contiguous memory region.
>   * @unmap_pages:  Unmap a range of virtually contiguous pages of the same size.
>   * @iova_to_phys: Translate iova to physical address.
> @@ -153,6 +154,9 @@ struct io_pgtable_cfg {
>  struct io_pgtable_ops {
>  	int (*map)(struct io_pgtable_ops *ops, unsigned long iova,
>  		   phys_addr_t paddr, size_t size, int prot, gfp_t gfp);
> +	int (*map_pages)(struct io_pgtable_ops *ops, unsigned long iova,
> +			 phys_addr_t paddr, size_t pgsize, size_t pgcount,
> +			 int prot, gfp_t gfp, size_t *mapped);

How about returning 'size_t' and using IS_ERR_VALUE() instead of adding
the extra 'mapped' argument (i.e. return the size of the region mapped
or an error code)? I don't think we realistically need to care about map
sizes that overlap with the error region.

Will

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