Re: [PATCH 3/7] ACPI/IORT: Handle memory address size limits as limits

[Will Deacon]

On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote:
> Return the Root Complex/Named Component memory address size limit as an
> inclusive limit value, rather than an exclusive size.  This saves us
> having to special-case 64-bit overflow, and simplifies our caller too.
> 
> Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> ---
>  drivers/acpi/arm64/dma.c  |  9 +++------
>  drivers/acpi/arm64/iort.c | 18 ++++++++----------
>  include/linux/acpi_iort.h |  4 ++--
>  3 files changed, 13 insertions(+), 18 deletions(-)

[...]

> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index 6496ff5a6ba2..eb64d8e17dd1 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id)
>  { return -ENODEV; }
>  #endif
>  
> -static int nc_dma_get_range(struct device *dev, u64 *size)
> +static int nc_dma_get_range(struct device *dev, u64 *limit)
>  {
>  	struct acpi_iort_node *node;
>  	struct acpi_iort_named_component *ncomp;
> @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size)
>  		return -EINVAL;
>  	}
>  
> -	*size = ncomp->memory_address_limit >= 64 ? U64_MAX :
> -			1ULL<<ncomp->memory_address_limit;
> +	*limit = (1ULL << ncomp->memory_address_limit) - 1;

The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe
to drop that? You mention it in the cover letter, so clearly I'm missing
something!

>  
>  	return 0;
>  }
>  
> -static int rc_dma_get_range(struct device *dev, u64 *size)
> +static int rc_dma_get_range(struct device *dev, u64 *limit)
>  {
>  	struct acpi_iort_node *node;
>  	struct acpi_iort_root_complex *rc;
> @@ -1408,8 +1407,7 @@ static int rc_dma_get_range(struct device *dev, u64 *size)
>  		return -EINVAL;
>  	}
>  
> -	*size = rc->memory_address_limit >= 64 ? U64_MAX :
> -			1ULL<<rc->memory_address_limit;
> +	*limit = (1ULL << rc->memory_address_limit) - 1;

Same thing here.

Will