[PATCH 16/19] iommu/amd: Use roundup_pow_two() instead of get_order()

[Robin Murphy]

On 2025-02-04 6:34 pm, Jason Gunthorpe wrote:
>    1 << (get_order(x) + PAGE_SHIFT) ==  roundup_pow_two()

...unless x < 2048, which does seem possible here if last_bdf is 
sufficiently small. Not too significant in the cases where the result is 
only rounded back up again for an allocation or remap anyway, but I do 
wonder about the use of dev_table_size in iommu_set_device_table(), and 
whether this change might break it, or whether it's already wrong for 
that case and this might actually fix it...

Thanks,
Robin.

> Use the shorter version.
> 
> Signed-off-by: Jason Gunthorpe <jgg at nvidia.com>
> ---
>   drivers/iommu/amd/init.c | 5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index f1c5041647173c..7d77929bc63af3 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -247,10 +247,7 @@ static void init_translation_status(struct amd_iommu *iommu)
>   
>   static inline unsigned long tbl_size(int entry_size, int last_bdf)
>   {
> -	unsigned shift = PAGE_SHIFT +
> -			 get_order((last_bdf + 1) * entry_size);
> -
> -	return 1UL << shift;
> +	return roundup_pow_of_two((last_bdf + 1) * entry_size);
>   }
>   
>   int amd_iommu_get_num_iommus(void)