linux-kernel - Re: [PATCH] microblaze: Fix mmap for cache coherent memory

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Date:	Wed, 10 Dec 2014 10:27:52 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Lars-Peter Clausen <lars@...afoo.de>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] microblaze: Fix mmap for cache coherent memory

On 12/03/2014 04:07 PM, Lars-Peter Clausen wrote:
> When running in non-cache coherent configuration the memory that was
> allocated with dma_alloc_coherent() has a custom mapping and so there is no
> 1-to-1 relationship between the kernel virtual address and the PFN. This
> means that virt_to_pfn() will not work correctly for those addresses and the
> default mmap implementation in the form of dma_common_mmap() will map some
> random, but not the requested, memory area.
> 
> Fix this by providing a custom mmap implementation that looks up the PFN
> from the page table rather than using virt_to_pfn.
> 
> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> ---
>  arch/microblaze/include/asm/pgtable.h |  1 +
>  arch/microblaze/kernel/dma.c          | 26 ++++++++++++++++++++++++++
>  arch/microblaze/mm/consistent.c       | 23 ++++++++++++++++++-----
>  3 files changed, 45 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/microblaze/include/asm/pgtable.h b/arch/microblaze/include/asm/pgtable.h
> index 95cef0b..df19d0c 100644
> --- a/arch/microblaze/include/asm/pgtable.h
> +++ b/arch/microblaze/include/asm/pgtable.h
> @@ -565,6 +565,7 @@ void consistent_free(size_t size, void *vaddr);
>  void consistent_sync(void *vaddr, size_t size, int direction);
>  void consistent_sync_page(struct page *page, unsigned long offset,
>  	size_t size, int direction);
> +unsigned long consistent_virt_to_pfn(void *vaddr);
>  
>  void setup_memory(void);
>  #endif /* __ASSEMBLY__ */
> diff --git a/arch/microblaze/kernel/dma.c b/arch/microblaze/kernel/dma.c
> index 4633c36..4822367 100644
> --- a/arch/microblaze/kernel/dma.c
> +++ b/arch/microblaze/kernel/dma.c
> @@ -154,9 +154,35 @@ dma_direct_sync_sg_for_device(struct device *dev,
>  			__dma_sync(sg->dma_address, sg->length, direction);
>  }
>  
> +int dma_direct_mmap_coherent(struct device *dev, struct vm_area_struct *vma,
> +			     void *cpu_addr, dma_addr_t handle, size_t size,
> +			     struct dma_attrs *attrs)
> +{
> +	unsigned long user_count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> +	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +	unsigned long off = vma->vm_pgoff;
> +	unsigned long pfn;
> +
> +	if (!IS_ENABLED(CONFIG_MMU))
> +		return -ENXIO;
> +
> +	if (off >= count || user_count > (count - off))
> +		return -ENXIO;
> +
> +#ifdef NOT_COHERENT_CACHE
> +	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> +	pfn = consistent_virt_to_pfn(cpu_addr);
> +#else
> +	pfn = virt_to_pfn(cpu_addr);
> +#endif
> +	return remap_pfn_range(vma, vma->vm_start, pfn + off,
> +			       vma->vm_end - vma->vm_start, vma->vm_page_prot);
> +}
> +
>  struct dma_map_ops dma_direct_ops = {
>  	.alloc		= dma_direct_alloc_coherent,
>  	.free		= dma_direct_free_coherent,
> +	.mmap		= dma_direct_mmap_coherent,
>  	.map_sg		= dma_direct_map_sg,
>  	.dma_supported	= dma_direct_dma_supported,
>  	.map_page	= dma_direct_map_page,
> diff --git a/arch/microblaze/mm/consistent.c b/arch/microblaze/mm/consistent.c
> index e10ad93..f358cd2 100644
> --- a/arch/microblaze/mm/consistent.c
> +++ b/arch/microblaze/mm/consistent.c
> @@ -156,6 +156,23 @@ void *consistent_alloc(gfp_t gfp, size_t size, dma_addr_t *dma_handle)
>  }
>  EXPORT_SYMBOL(consistent_alloc);
>  
> +static pte_t *consistent_virt_to_pte(void *vaddr)
> +{
> +	unsigned long addr = (unsigned long)vaddr;
> +
> +	return pte_offset_kernel(pmd_offset(pgd_offset_k(addr), addr), addr);
> +}
> +
> +unsigned long consistent_virt_to_pfn(void *vaddr)
> +{
> +	pte_t *ptep = consistent_virt_to_pte(vaddr);
> +
> +	if (pte_none(*ptep) || !pte_present(*ptep))
> +		return 0;
> +
> +	return pte_pfn(*ptep);
> +}
> +
>  /*
>   * free page(s) as defined by the above mapping.
>   */
> @@ -181,13 +198,9 @@ void consistent_free(size_t size, void *vaddr)
>  	} while (size -= PAGE_SIZE);
>  #else
>  	do {
> -		pte_t *ptep;
> +		pte_t *ptep = consistent_virt_to_pte(vaddr);
>  		unsigned long pfn;
>  
> -		ptep = pte_offset_kernel(pmd_offset(pgd_offset_k(
> -						(unsigned int)vaddr),
> -					(unsigned int)vaddr),
> -				(unsigned int)vaddr);
>  		if (!pte_none(*ptep) && pte_present(*ptep)) {
>  			pfn = pte_pfn(*ptep);
>  			pte_clear(&init_mm, (unsigned int)vaddr, ptep);
> 


Applied.

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform



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