[PATCH 3/8] swiotlb: factor out a nr_slots helper

[Robin Murphy]

On 2021-02-04 19:30, Christoph Hellwig wrote:
> Factor out a helper to find the number of slots for a given size.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>   kernel/dma/swiotlb.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 838dbad10ab916..0c0b81799edbdb 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -194,6 +194,11 @@ static inline unsigned long io_tlb_offset(unsigned long val)
>   	return val & (IO_TLB_SEGSIZE - 1);
>   }
>   
> +static unsigned long nr_slots(u64 val)
> +{
> +	return ALIGN(val, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;

Would DIV_ROUND_UP(val, 1 << IOTLB_SHIFT) be even clearer?

Robin.

> +}
> +
>   /*
>    * Early SWIOTLB allocation may be too early to allow an architecture to
>    * perform the desired operations.  This function allows the architecture to
> @@ -493,20 +498,20 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t orig_addr,
>   
>   	tbl_dma_addr &= mask;
>   
> -	offset_slots = ALIGN(tbl_dma_addr, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
> +	offset_slots = nr_slots(tbl_dma_addr);
>   
>   	/*
>   	 * Carefully handle integer overflow which can occur when mask == ~0UL.
>   	 */
>   	max_slots = mask + 1
> -		    ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
> +		    ? nr_slots(mask + 1)
>   		    : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);
>   
>   	/*
>   	 * For mappings greater than or equal to a page, we limit the stride
>   	 * (and hence alignment) to a page size.
>   	 */
> -	nslots = ALIGN(alloc_size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
> +	nslots = nr_slots(alloc_size);
>   	if (alloc_size >= PAGE_SIZE)
>   		stride = (1 << (PAGE_SHIFT - IO_TLB_SHIFT));
>   	else
> @@ -602,7 +607,7 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
>   			      enum dma_data_direction dir, unsigned long attrs)
>   {
>   	unsigned long flags;
> -	int i, count, nslots = ALIGN(alloc_size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
> +	int i, count, nslots = nr_slots(alloc_size);
>   	int index = (tlb_addr - io_tlb_start) >> IO_TLB_SHIFT;
>   	phys_addr_t orig_addr = io_tlb_orig_addr[index];
>   
>