Subject: Re: [PATCH 1/4] powerpc: Dynamic DMA zone limits

From: Anton Blanchard <[email-masked]>
Date: Mon, 13 Oct 2014 18:14:36 +1100

Hi Scott,

> Platform code can call limit_zone_pfn() to set appropriate limits
> for ZONE_DMA and ZONE_DMA32, and dma_direct_alloc_coherent() will
> select a suitable zone based on a device's mask and the pfn limits
> that platform code has configured.

This patch breaks my POWER8 box:

ipr 0001:08:00.0: Using 64-bit DMA iommu bypass
ipr 0001:08:00.0: dma_direct_alloc_coherent: No suitable zone for pfn 0x10000
ipr 0001:08:00.0: Couldn't allocate enough memory for device driver! 
ipr: probe of 0001:08:00.0 failed with error -12

ipr isn't setting a coherent mask, but we shouldn't care on these boxes.
Could we ignore the coherent mask or copy the dma mask to it?

Anton
--

> Signed-off-by: Scott Wood <[email-masked]>
> Cc: Shaohui Xie <[email-masked]>
> ---
>  arch/powerpc/Kconfig               |  4 +++
>  arch/powerpc/include/asm/pgtable.h |  3 ++
>  arch/powerpc/kernel/dma.c          | 20 +++++++++++++
>  arch/powerpc/mm/mem.c              | 61
> ++++++++++++++++++++++++++++++++++---- 4 files changed, 83
> insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 80b94b0..56dc47a 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -286,6 +286,10 @@ config PPC_EMULATE_SSTEP
>  	bool
>  	default y if KPROBES || UPROBES || XMON || HAVE_HW_BREAKPOINT
>  
> +config ZONE_DMA32
> +	bool
> +	default y if PPC64
> +
>  source "init/Kconfig"
>  
>  source "kernel/Kconfig.freezer"
> diff --git a/arch/powerpc/include/asm/pgtable.h
> b/arch/powerpc/include/asm/pgtable.h index d98c1ec..6d74167 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -4,6 +4,7 @@
>  
>  #ifndef __ASSEMBLY__
>  #include <linux/mmdebug.h>
> +#include <linux/mmzone.h>
>  #include <asm/processor.h>		/* For TASK_SIZE */
>  #include <asm/mmu.h>
>  #include <asm/page.h>
> @@ -281,6 +282,8 @@ extern unsigned long empty_zero_page[];
>  
>  extern pgd_t swapper_pg_dir[];
>  
> +void limit_zone_pfn(enum zone_type zone, unsigned long max_pfn);
> +int dma_pfn_limit_to_zone(u64 pfn_limit);
>  extern void paging_init(void);
>  
>  /*
> diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c
> index ee78f6e..dfd99ef 100644
> --- a/arch/powerpc/kernel/dma.c
> +++ b/arch/powerpc/kernel/dma.c
> @@ -40,6 +40,26 @@ void *dma_direct_alloc_coherent(struct device
> *dev, size_t size, #else
>  	struct page *page;
>  	int node = dev_to_node(dev);
> +	u64 pfn = (dev->coherent_dma_mask >> PAGE_SHIFT) + 1;
> +	int zone;
> +
> +	zone = dma_pfn_limit_to_zone(pfn);
> +	if (zone < 0) {
> +		dev_err(dev, "%s: No suitable zone for pfn %#llx\n",
> +			__func__, pfn);
> +		return NULL;
> +	}
> +
> +	switch (zone) {
> +	case ZONE_DMA:
> +		flag |= GFP_DMA;
> +		break;
> +#ifdef CONFIG_ZONE_DMA32
> +	case ZONE_DMA32:
> +		flag |= GFP_DMA32;
> +		break;
> +#endif
> +	};
>  
>  	/* ignore region specifiers */
>  	flag  &= ~(__GFP_HIGHMEM);
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index e0f7a18..3b23e17 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -261,6 +261,54 @@ static int __init mark_nonram_nosave(void)
>  	return 0;
>  }
>  
> +static bool zone_limits_final;
> +
> +static unsigned long max_zone_pfns[MAX_NR_ZONES] = {
> +	[0 ... MAX_NR_ZONES - 1] = ~0UL
> +};
> +
> +/*
> + * Restrict the specified zone and all more restrictive zones
> + * to be below the specified pfn.  May not be called after
> + * paging_init().
> + */
> +void __init limit_zone_pfn(enum zone_type zone, unsigned long
> pfn_limit) +{
> +	int i;
> +
> +	if (WARN_ON(zone_limits_final))
> +		return;
> +
> +	for (i = zone; i >= 0; i--) {
> +		if (max_zone_pfns[i] > pfn_limit)
> +			max_zone_pfns[i] = pfn_limit;
> +	}
> +}
> +
> +/*
> + * Find the least restrictive zone that is entirely below the
> + * specified pfn limit.  Returns < 0 if no suitable zone is found.
> + *
> + * pfn_limit must be u64 because it can exceed 32 bits even on 32-bit
> + * systems -- the DMA limit can be higher than any possible real pfn.
> + */
> +int dma_pfn_limit_to_zone(u64 pfn_limit)
> +{
> +	enum zone_type top_zone = ZONE_NORMAL;
> +	int i;
> +
> +#ifdef CONFIG_HIGHMEM
> +	top_zone = ZONE_HIGHMEM;
> +#endif
> +
> +	for (i = top_zone; i >= 0; i--) {
> +		if (max_zone_pfns[i] <= pfn_limit)
> +			return i;
> +	}
> +
> +	return -EPERM;
> +}
> +
>  /*
>   * paging_init() sets up the page tables - in fact we've already
> done this. */
> @@ -268,7 +316,7 @@ void __init paging_init(void)
>  {
>  	unsigned long long total_ram = memblock_phys_mem_size();
>  	phys_addr_t top_of_ram = memblock_end_of_DRAM();
> -	unsigned long max_zone_pfns[MAX_NR_ZONES];
> +	enum zone_type top_zone;
>  
>  #ifdef CONFIG_PPC32
>  	unsigned long v = __fix_to_virt(__end_of_fixed_addresses -
> 1); @@ -290,13 +338,16 @@ void __init paging_init(void)
>  	       (unsigned long long)top_of_ram, total_ram);
>  	printk(KERN_DEBUG "Memory hole size: %ldMB\n",
>  	       (long int)((top_of_ram - total_ram) >> 20));
> -	memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
> +
>  #ifdef CONFIG_HIGHMEM
> -	max_zone_pfns[ZONE_DMA] = lowmem_end_addr >> PAGE_SHIFT;
> -	max_zone_pfns[ZONE_HIGHMEM] = top_of_ram >> PAGE_SHIFT;
> +	top_zone = ZONE_HIGHMEM;
> +	limit_zone_pfn(ZONE_NORMAL, lowmem_end_addr >> PAGE_SHIFT);
>  #else
> -	max_zone_pfns[ZONE_DMA] = top_of_ram >> PAGE_SHIFT;
> +	top_zone = ZONE_NORMAL;
>  #endif
> +
> +	limit_zone_pfn(top_zone, top_of_ram >> PAGE_SHIFT);
> +	zone_limits_final = true;
>  	free_area_init_nodes(max_zone_pfns);
>  
>  	mark_nonram_nosave();