Subject: [PATCHv4 2/2] ARM: dma-mapping: remove custom consistent dma region

From: [email-masked] (Minchan Kim)
Date: Wed, 27 Jun 2012 10:54:32 +0900

On 06/25/2012 05:47 PM, Marek Szyprowski wrote:

> This patch changes dma-mapping subsystem to use generic vmalloc areas
> for all consistent dma allocations. This increases the total size limit
> of the consistent allocations and removes platform hacks and a lot of
> duplicated code.
> 
> Atomic allocations are served from special pool preallocated on boot,
> becasue vmalloc areas cannot be reliably created in atomic context.

s/becasue/because

> 
> Signed-off-by: Marek Szyprowski <[email-masked]>
> Reviewed-by: Kyungmin Park <[email-masked]>

I like this patch very much but notice one more again. 
Here is goes, again.
https://lkml.org/lkml/2012/6/13/628
It's another hack for avoding vmalloc atomic.
There are several grumblers ago and everybody made own mempool so code
began to bloat and it would be error-prone. :(
I think it's TODO for mm folks to decide.

Anyway, there are some trivial comment below.

> ---
>  Documentation/kernel-parameters.txt |    2 +-
>  arch/arm/include/asm/dma-mapping.h  |    2 +-
>  arch/arm/mm/dma-mapping.c           |  505 +++++++++++++----------------------
>  arch/arm/mm/mm.h                    |    3 +
>  include/linux/vmalloc.h             |    1 +
>  mm/vmalloc.c                        |   10 +-
>  6 files changed, 194 insertions(+), 329 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index a92c5eb..da07f6c 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -526,7 +526,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  
>  	coherent_pool=nn[KMG]	[ARM,KNL]
>  			Sets the size of memory pool for coherent, atomic dma
> -			allocations if Contiguous Memory Allocator (CMA) is used.
> +			allocations.

What's the default? 256K?
If we specify, couldn't it help?

>  
>  	code_bytes	[X86] How many bytes of object code to print
>  			in an oops report.
> diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
> index bbef15d..80777d87 100644
> --- a/arch/arm/include/asm/dma-mapping.h
> +++ b/arch/arm/include/asm/dma-mapping.h
> @@ -226,7 +226,7 @@ static inline int dma_mmap_writecombine(struct device *dev, struct vm_area_struc
>   * DMA region above it's default value of 2MB. It must be called before the
>   * memory allocator is initialised, i.e. before any core_initcall.
>   */
> -extern void __init init_consistent_dma_size(unsigned long size);
> +static inline void init_consistent_dma_size(unsigned long size) { }
>  
>  /*
>   * For SA-1111, IXP425, and ADI systems  the dma-mapping functions are "magic"
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index d766e42..c1f2294 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -22,6 +22,7 @@
>  #include <linux/memblock.h>
>  #include <linux/slab.h>
>  #include <linux/iommu.h>
> +#include <linux/io.h>
>  #include <linux/vmalloc.h>
>  
>  #include <asm/memory.h>
> @@ -217,115 +218,67 @@ static void __dma_free_buffer(struct page *page, size_t size)
>  }
>  
>  #ifdef CONFIG_MMU
> -
> -#define CONSISTENT_OFFSET(x)	(((unsigned long)(x) - consistent_base) >> PAGE_SHIFT)
> -#define CONSISTENT_PTE_INDEX(x) (((unsigned long)(x) - consistent_base) >> PMD_SHIFT)
> -
> -/*
> - * These are the page tables (2MB each) covering uncached, DMA consistent allocations
> - */
> -static pte_t **consistent_pte;
> -
> -#define DEFAULT_CONSISTENT_DMA_SIZE SZ_2M
> -
> -static unsigned long consistent_base = CONSISTENT_END - DEFAULT_CONSISTENT_DMA_SIZE;
> -
> -void __init init_consistent_dma_size(unsigned long size)
> -{
> -	unsigned long base = CONSISTENT_END - ALIGN(size, SZ_2M);
> -
> -	BUG_ON(consistent_pte); /* Check we're called before DMA region init */
> -	BUG_ON(base < VMALLOC_END);
> -
> -	/* Grow region to accommodate specified size  */
> -	if (base < consistent_base)
> -		consistent_base = base;
> -}
> -
> -#include "vmregion.h"
> -
> -static struct arm_vmregion_head consistent_head = {
> -	.vm_lock	= __SPIN_LOCK_UNLOCKED(&consistent_head.vm_lock),
> -	.vm_list	= LIST_HEAD_INIT(consistent_head.vm_list),
> -	.vm_end		= CONSISTENT_END,
> -};
> -
>  #ifdef CONFIG_HUGETLB_PAGE
>  #error ARM Coherent DMA allocator does not (yet) support huge TLB
>  #endif
>  
> -/*
> - * Initialise the consistent memory allocation.
> - */
> -static int __init consistent_init(void)
> -{
> -	int ret = 0;
> -	pgd_t *pgd;
> -	pud_t *pud;
> -	pmd_t *pmd;
> -	pte_t *pte;
> -	int i = 0;
> -	unsigned long base = consistent_base;
> -	unsigned long num_ptes = (CONSISTENT_END - base) >> PMD_SHIFT;
> -
> -	if (IS_ENABLED(CONFIG_CMA) && !IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU))
> -		return 0;
> -
> -	consistent_pte = kmalloc(num_ptes * sizeof(pte_t), GFP_KERNEL);
> -	if (!consistent_pte) {
> -		pr_err("%s: no memory\n", __func__);
> -		return -ENOMEM;
> -	}
> -
> -	pr_debug("DMA memory: 0x%08lx - 0x%08lx:\n", base, CONSISTENT_END);
> -	consistent_head.vm_start = base;
> -
> -	do {
> -		pgd = pgd_offset(&init_mm, base);
> -
> -		pud = pud_alloc(&init_mm, pgd, base);
> -		if (!pud) {
> -			pr_err("%s: no pud tables\n", __func__);
> -			ret = -ENOMEM;
> -			break;
> -		}
> -
> -		pmd = pmd_alloc(&init_mm, pud, base);
> -		if (!pmd) {
> -			pr_err("%s: no pmd tables\n", __func__);
> -			ret = -ENOMEM;
> -			break;
> -		}
> -		WARN_ON(!pmd_none(*pmd));
> -
> -		pte = pte_alloc_kernel(pmd, base);
> -		if (!pte) {
> -			pr_err("%s: no pte tables\n", __func__);
> -			ret = -ENOMEM;
> -			break;
> -		}
> -
> -		consistent_pte[i++] = pte;
> -		base += PMD_SIZE;
> -	} while (base < CONSISTENT_END);
> -
> -	return ret;
> -}
> -core_initcall(consistent_init);
> -
>  static void *__alloc_from_contiguous(struct device *dev, size_t size,
>  				     pgprot_t prot, struct page **ret_page);
>  
> -static struct arm_vmregion_head coherent_head = {
> -	.vm_lock	= __SPIN_LOCK_UNLOCKED(&coherent_head.vm_lock),
> -	.vm_list	= LIST_HEAD_INIT(coherent_head.vm_list),
> +static void *__alloc_remap_buffer(struct device *dev, size_t size, gfp_t gfp,
> +				 pgprot_t prot, struct page **ret_page,
> +				 const void *caller);
> +
> +static void *
> +__dma_alloc_remap(struct page *page, size_t size, gfp_t gfp, pgprot_t prot,
> +	const void *caller)
> +{
> +	struct vm_struct *area;
> +	unsigned long addr;
> +
> +	area = get_vm_area_caller(size, VM_ARM_DMA_CONSISTENT | VM_USERMAP,
> +				  caller);

Please write down why we always need VM_USERMAP.
If we always need it in ARM, why don't you define following as?
#define VM_ARM_DMA_CONSISTENT (0x20000000 | VM_USERAMP)?
Although it's trivial, it could be more understandable that everybody
can think of it that "ARM DMA allocation could be mapped by user space, everytime"

> +	if (!area)
> +		return NULL;
> +	addr = (unsigned long)area->addr;
> +	area->phys_addr = __pfn_to_phys(page_to_pfn(page));
> +
> +	if (ioremap_page_range(addr, addr + size, area->phys_addr, prot)) {
> +		vunmap((void *)addr);
> +		return NULL;
> +	}
> +	return (void *)addr;
> +}
> +
> +static void __dma_free_remap(void *cpu_addr, size_t size)
> +{
> +	struct vm_struct *area = find_vm_area(cpu_addr);
> +	if (!area || !(area->flags & VM_ARM_DMA_CONSISTENT)) {

Above definery could enhance this check, too.

> +		pr_err("%s: trying to free invalid coherent area: %p\n",
> +		       __func__, cpu_addr);
> +		dump_stack();
> +		return;
> +	}
> +	unmap_kernel_range((unsigned long)cpu_addr, size);
> +	vunmap(cpu_addr);
> +}
> +
> +struct dma_pool {
> +	size_t size;
> +	spinlock_t lock;
> +	unsigned long *bitmap;
> +	unsigned long nr_pages;
> +	void *vaddr;
> +	struct page *page;
>  };
>  
> -static size_t coherent_pool_size = DEFAULT_CONSISTENT_DMA_SIZE / 8;
> +static struct dma_pool atomic_pool = {
> +	.size = SZ_256K,
> +};
>  
>  static int __init early_coherent_pool(char *p)
>  {
> -	coherent_pool_size = memparse(p, &p);
> +	atomic_pool.size = memparse(p, &p);
>  	return 0;
>  }
>  early_param("coherent_pool", early_coherent_pool);
> @@ -333,32 +286,45 @@ early_param("coherent_pool", early_coherent_pool);
>  /*
>   * Initialise the coherent pool for atomic allocations.
>   */
> -static int __init coherent_init(void)
> +static int __init atomic_pool_init(void)
>  {
> +	struct dma_pool *pool = &atomic_pool;
>  	pgprot_t prot = pgprot_dmacoherent(pgprot_kernel);
> -	size_t size = coherent_pool_size;
> +	unsigned long nr_pages = pool->size >> PAGE_SHIFT;
> +	unsigned long *bitmap;
>  	struct page *page;
>  	void *ptr;
> +	int bitmap_size = BITS_TO_LONGS(nr_pages) * sizeof(long);
>  
> -	if (!IS_ENABLED(CONFIG_CMA))
> -		return 0;
> +	bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> +	if (!bitmap)
> +		goto no_bitmap;
>  
> -	ptr = __alloc_from_contiguous(NULL, size, prot, &page);
> +	if (IS_ENABLED(CONFIG_CMA))
> +		ptr = __alloc_from_contiguous(NULL, pool->size, prot, &page);
> +	else
> +		ptr = __alloc_remap_buffer(NULL, pool->size, GFP_KERNEL, prot,
> +					   &page, NULL);
>  	if (ptr) {
> -		coherent_head.vm_start = (unsigned long) ptr;
> -		coherent_head.vm_end = (unsigned long) ptr + size;
> -		printk(KERN_INFO "DMA: preallocated %u KiB pool for atomic coherent allocations\n",
> -		       (unsigned)size / 1024);
> +		spin_lock_init(&pool->lock);
> +		pool->vaddr = ptr;
> +		pool->page = page;
> +		pool->bitmap = bitmap;
> +		pool->nr_pages = nr_pages;
> +		pr_info("DMA: preallocated %u KiB pool for atomic coherent allocations\n",
> +		       (unsigned)pool->size / 1024);
>  		return 0;
>  	}
> -	printk(KERN_ERR "DMA: failed to allocate %u KiB pool for atomic coherent allocation\n",
> -	       (unsigned)size / 1024);
> +	kfree(bitmap);
> +no_bitmap:
> +	pr_err("DMA: failed to allocate %u KiB pool for atomic coherent allocation\n",
> +	       (unsigned)pool->size / 1024);
>  	return -ENOMEM;
>  }
>  /*
>   * CMA is activated by core_initcall, so we must be called after it.
>   */
> -postcore_initcall(coherent_init);
> +postcore_initcall(atomic_pool_init);
>  
>  struct dma_contig_early_reserve {
>  	phys_addr_t base;
> @@ -406,112 +372,6 @@ void __init dma_contiguous_remap(void)
>  	}
>  }
>  
> -static void *
> -__dma_alloc_remap(struct page *page, size_t size, gfp_t gfp, pgprot_t prot,
> -	const void *caller)
> -{
> -	struct arm_vmregion *c;
> -	size_t align;
> -	int bit;
> -
> -	if (!consistent_pte) {
> -		pr_err("%s: not initialised\n", __func__);
> -		dump_stack();
> -		return NULL;
> -	}
> -
> -	/*
> -	 * Align the virtual region allocation - maximum alignment is
> -	 * a section size, minimum is a page size.  This helps reduce
> -	 * fragmentation of the DMA space, and also prevents allocations
> -	 * smaller than a section from crossing a section boundary.
> -	 */
> -	bit = fls(size - 1);
> -	if (bit > SECTION_SHIFT)
> -		bit = SECTION_SHIFT;
> -	align = 1 << bit;
> -
> -	/*
> -	 * Allocate a virtual address in the consistent mapping region.
> -	 */
> -	c = arm_vmregion_alloc(&consistent_head, align, size,
> -			    gfp & ~(__GFP_DMA | __GFP_HIGHMEM), caller);
> -	if (c) {
> -		pte_t *pte;
> -		int idx = CONSISTENT_PTE_INDEX(c->vm_start);
> -		u32 off = CONSISTENT_OFFSET(c->vm_start) & (PTRS_PER_PTE-1);
> -
> -		pte = consistent_pte[idx] + off;
> -		c->priv = page;
> -
> -		do {
> -			BUG_ON(!pte_none(*pte));
> -
> -			set_pte_ext(pte, mk_pte(page, prot), 0);
> -			page++;
> -			pte++;
> -			off++;
> -			if (off >= PTRS_PER_PTE) {
> -				off = 0;
> -				pte = consistent_pte[++idx];
> -			}
> -		} while (size -= PAGE_SIZE);
> -
> -		dsb();
> -
> -		return (void *)c->vm_start;
> -	}
> -	return NULL;
> -}
> -
> -static void __dma_free_remap(void *cpu_addr, size_t size)
> -{
> -	struct arm_vmregion *c;
> -	unsigned long addr;
> -	pte_t *ptep;
> -	int idx;
> -	u32 off;
> -
> -	c = arm_vmregion_find_remove(&consistent_head, (unsigned long)cpu_addr);
> -	if (!c) {
> -		pr_err("%s: trying to free invalid coherent area: %p\n",
> -		       __func__, cpu_addr);
> -		dump_stack();
> -		return;
> -	}
> -
> -	if ((c->vm_end - c->vm_start) != size) {
> -		pr_err("%s: freeing wrong coherent size (%ld != %d)\n",
> -		       __func__, c->vm_end - c->vm_start, size);
> -		dump_stack();
> -		size = c->vm_end - c->vm_start;
> -	}
> -
> -	idx = CONSISTENT_PTE_INDEX(c->vm_start);
> -	off = CONSISTENT_OFFSET(c->vm_start) & (PTRS_PER_PTE-1);
> -	ptep = consistent_pte[idx] + off;
> -	addr = c->vm_start;
> -	do {
> -		pte_t pte = ptep_get_and_clear(&init_mm, addr, ptep);
> -
> -		ptep++;
> -		addr += PAGE_SIZE;
> -		off++;
> -		if (off >= PTRS_PER_PTE) {
> -			off = 0;
> -			ptep = consistent_pte[++idx];
> -		}
> -
> -		if (pte_none(pte) || !pte_present(pte))
> -			pr_crit("%s: bad page in kernel page table\n",
> -				__func__);
> -	} while (size -= PAGE_SIZE);
> -
> -	flush_tlb_kernel_range(c->vm_start, c->vm_end);
> -
> -	arm_vmregion_free(&consistent_head, c);
> -}
> -
>  static int __dma_update_pte(pte_t *pte, pgtable_t token, unsigned long addr,
>  			    void *data)
>  {
> @@ -552,15 +412,17 @@ static void *__alloc_remap_buffer(struct device *dev, size_t size, gfp_t gfp,
>  	return ptr;
>  }
>  
> -static void *__alloc_from_pool(struct device *dev, size_t size,
> -			       struct page **ret_page, const void *caller)
> +static void *__alloc_from_pool(size_t size, struct page **ret_page)
>  {
> -	struct arm_vmregion *c;
> +	struct dma_pool *pool = &atomic_pool;
> +	unsigned int count = size >> PAGE_SHIFT;

Just out of curiosity.
Do we make sure size is always aligned to PAGE_SIZE?
If so, please write down

> +	unsigned int pageno;
> +	unsigned long flags;
> +	void *ptr = NULL;
>  	size_t align;
>  
> -	if (!coherent_head.vm_start) {
> -		printk(KERN_ERR "%s: coherent pool not initialised!\n",
> -		       __func__);
> +	if (!pool->vaddr) {
> +		pr_err("%s: coherent pool not initialised!\n", __func__);
>  		dump_stack();

Why doesn't you use WARN?

>  		return NULL;
>  	}

< snip>

-- 

Kind regards,
Minchan Kim