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From: Robin Murphy <robin.murphy@arm.com>
To: Pankaj Suryawanshi <pankajssuryawanshi@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	linux-mm@kvack.org, iommu@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, Vlastimil Babka <vbabka@suse.cz>,
	Michal Hocko <mhocko@kernel.org>
Subject: Re: DMA-API attr - DMA_ATTR_NO_KERNEL_MAPPING
Date: Mon, 1 Jul 2019 18:54:47 +0100	[thread overview]
Message-ID: <0725b9aa-0523-daef-b4ff-7e2dd910cf3c@arm.com> (raw)
In-Reply-To: <CACDBo57CcYQmNrsTdMbax27nbLyeMQu4kfKZOzNczNcnde9g3Q@mail.gmail.com>

On 01/07/2019 18:47, Pankaj Suryawanshi wrote:
>> If you want a kernel mapping, *don't* explicitly request not to have a
>> kernel mapping in the first place. It's that simple.
>>
> 
> Do you mean do not use dma-api ? because if i used dma-api it will give you
> mapped virtual address.
> or i have to use directly cma_alloc() in my driver. // if i used this
> approach i need to reserved more vmalloc area.

No, I mean just call dma_alloc_attrs() normally *without* adding the 
DMA_ATTR_NO_KERNEL_MAPPING flag. That flag means "I never ever want to 
make CPU accesses to this buffer from the kernel" - that is clearly not 
the case for your code, so it is utterly nonsensical to still pass the 
flag but try to hack around it later.

Robin.


  parent reply	other threads:[~2019-07-01 17:54 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-26 16:41 Pankaj Suryawanshi
2019-06-26 16:42 ` Pankaj Suryawanshi
2019-06-26 17:51   ` Christoph Hellwig
2019-06-28 16:29     ` Pankaj Suryawanshi
2019-07-01 14:09       ` Robin Murphy
2019-07-01 17:47         ` Pankaj Suryawanshi
2019-07-01 17:52           ` Pankaj Suryawanshi
2019-07-01 17:54           ` Robin Murphy [this message]
2019-07-01 18:07             ` Pankaj Suryawanshi
2019-07-01 18:36           ` Pankaj Suryawanshi

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