Re: [PATCH kernel] powerps/pseries/dma: Add support for 2M IOMMU page size

[Frederic Barrat <fbarrat@linux.ibm.com>]

On 28/09/2021 12:15, Alexey Kardashevskiy wrote:
> The upcoming PAPR spec adds a 2M page size, bit 23 right after the 16G page
> size in the "ibm,query-pe-dma-window" call.
> 
> This adds support for the new page size. Since the new page size is out
> of sorted order, this changes the loop to not assume that shift[] is
> sorted.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---


Looks ok to me
Reviewed-by: Frederic Barrat <fbarrat@linux.ibm.com>


> 
> This might not work if PHYP keeps rejecting new window requests for less
> than 32768 TCEs. This is needed:
> https://github.com/aik/linux/commit/8cc8fa5ba5b3b4a18efbc9d81d9e5b85ca7c8a95
> 
> 
> ---
>   arch/powerpc/platforms/pseries/iommu.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> index c741689a5165..237bf405b0cb 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -1159,14 +1159,15 @@ static void reset_dma_window(struct pci_dev *dev, struct device_node *par_dn)
>   /* Return largest page shift based on "IO Page Sizes" output of ibm,query-pe-dma-window. */
>   static int iommu_get_page_shift(u32 query_page_size)
>   {
> -	/* Supported IO page-sizes according to LoPAR */
> +	/* Supported IO page-sizes according to LoPAR, note that 2M is out of order */
>   	const int shift[] = {
>   		__builtin_ctzll(SZ_4K),   __builtin_ctzll(SZ_64K), __builtin_ctzll(SZ_16M),
>   		__builtin_ctzll(SZ_32M),  __builtin_ctzll(SZ_64M), __builtin_ctzll(SZ_128M),
> -		__builtin_ctzll(SZ_256M), __builtin_ctzll(SZ_16G)
> +		__builtin_ctzll(SZ_256M), __builtin_ctzll(SZ_16G), __builtin_ctzll(SZ_2M)
>   	};
>   
>   	int i = ARRAY_SIZE(shift) - 1;
> +	int ret = 0;
>   
>   	/*
>   	 * On LoPAR, ibm,query-pe-dma-window outputs "IO Page Sizes" using a bit field:
> @@ -1176,11 +1177,10 @@ static int iommu_get_page_shift(u32 query_page_size)
>   	 */
>   	for (; i >= 0 ; i--) {
>   		if (query_page_size & (1 << i))
> -			return shift[i];
> +			ret = max(ret, shift[i]);
>   	}
>   
> -	/* No valid page size found. */
> -	return 0;
> +	return ret;
>   }
>   
>   static struct property *ddw_property_create(const char *propname, u32 liobn, u64 dma_addr,
>