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

[Leonardo Brás]

Hello Alexey,

On Tue, 2021-09-28 at 20:15 +1000, 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 at ozlabs.ru>
> ---
> 
> 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,

Looks great to me.

FWIW:
Reviewed-by: Leonardo Bras <leobras.c at gmail.com>

Best regards,
Leonardo