Re: [PATCH v5 2/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging

[Matthew Wilcox]

On Fri, Dec 07, 2018 at 02:16:19PM +0800, Nicolas Boichat wrote:
> +#ifdef CONFIG_ZONE_DMA32
> +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA32
> +#define ARM_V7S_TABLE_SLAB_CACHE SLAB_CACHE_DMA32

This name doesn't make any sense.  Why not ARM_V7S_TABLE_SLAB_FLAGS ?

> +#else
> +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA
> +#define ARM_V7S_TABLE_SLAB_CACHE SLAB_CACHE_DMA

Can you remind me again why it is, on machines which don't support
ZONE_DMA32, why we have to allocate from ZONE_DMA?  My understanding
is that 64-bit machines have ZONE_DMA32 and 32-bit machines don't.
So shouldn't this rather be GFP_KERNEL?

Actually, maybe we could centralise this in gfp.h:

#ifdef CONFIG_64BIT
# ifdef CONFIG_ZONE_DMA32
#define GFP_32BIT	GFP_DMA32
# else
#define GFP_32BIT	GFP_DMA
#else /* 32-bit */
#define GFP_32BIT	GFP_KERNEL
#endif