From: m.szyprowski@samsung•com (Marek Szyprowski)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] ARM64: dma-mapping: fix IOMMU-based dma_mmap_atts() implementation
Date: Wed, 17 Feb 2016 09:55:33 +0100 [thread overview]
Message-ID: <56C43585.9030502@samsung.com> (raw)
In-Reply-To: <56C339FD.6040907@arm.com>
Hello,
On 2016-02-16 16:02, Robin Murphy wrote:
> Hi Marek,
>
> On 16/02/16 14:14, Marek Szyprowski wrote:
>> IOMMU-based DMA-mapping implementation doesn't support
>> dma_declare_coherent() based regions, so there is no point to call
>> dma_mmap_from_coherent() from __iommu_mmap_atts(). This patch removes
>> useless code.
>
> I'm not sure that's the case - AFAICS a device could still have its
> own local memory despite being behind an IOMMU relative to the rest of
> the system. If it uses dma_declare_coherent() for that, the .alloc and
> .free callbacks here might be bypassed by dma_{alloc,free}_attrs()
> short-circuiting into dma_{alloc,release}_from_coherent(), but in the
> case of dma_mmap_attrs() it hits the .mmap callback first and only
> falls back to the from_coherent check in dma_common_mmap() if that
> isn't implemented.
Okay, I've missed that alloc/free_from_coherent is handled in generic
include/linux/dma-mapping.h. It is still a bit strange case with no real
user, but if this code is already there, then let it be.
>
> Maybe the right thing to do would be to move this check (with its
> associated guards) out from dma_common_mmap() up to dma_mmap_attrs()
> to be consistent with alloc/free; so that it doesn't need to be
> reimplemented all over arch/{arm,arm64,mips} at all?
>
That might be a good idea, although I'm not sure how portable is
pgprot_dmacoherent(), which will be needed by such common code.
Please ignore my patch then.
> Robin.
>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung•com>
>> ---
>> arch/arm64/mm/dma-mapping.c | 5 -----
>> 1 file changed, 5 deletions(-)
>>
>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
>> index 331c4ca..573b1e6 100644
>> --- a/arch/arm64/mm/dma-mapping.c
>> +++ b/arch/arm64/mm/dma-mapping.c
>> @@ -636,14 +636,9 @@ static int __iommu_mmap_attrs(struct device
>> *dev, struct vm_area_struct *vma,
>> struct dma_attrs *attrs)
>> {
>> struct vm_struct *area;
>> - int ret;
>>
>> vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot,
>> is_device_dma_coherent(dev));
>> -
>> - if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret))
>> - return ret;
>> -
>> area = find_vm_area(cpu_addr);
>> if (WARN_ON(!area || !area->pages))
>> return -ENXIO;
>
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
prev parent reply other threads:[~2016-02-17 8:55 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-16 14:14 [PATCH] ARM64: dma-mapping: fix IOMMU-based dma_mmap_atts() implementation Marek Szyprowski
2016-02-16 15:02 ` Robin Murphy
2016-02-17 8:55 ` Marek Szyprowski [this message]
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