linux-kernel - Re: For the problem when using swiotlb

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Message-ID: <546DA795.9080209@huawei.com>
Date:	Thu, 20 Nov 2014 16:34:29 +0800
From:	Ding Tianhong <dingtianhong@...wei.com>
To:	Arnd Bergmann <arnd@...db.de>,
	<linux-arm-kernel@...ts.infradead.org>
CC:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: For the problem when using swiotlb

On 2014/11/20 15:40, Arnd Bergmann wrote:
> On Thursday 20 November 2014 10:57:53 Ding Tianhong wrote:
>> On 2014/11/19 16:45, Arnd Bergmann wrote:
>>> On Wednesday 19 November 2014 11:17:15 Ding Tianhong wrote:
>>>> On 2014/11/18 2:09, Catalin Marinas wrote:
>>>>> On Mon, Nov 17, 2014 at 12:18:42PM +0000, Arnd Bergmann wrote:
>>>> Thanks everyone, I think I found the way to fix it, need to enable DMA_CMA, to reserve a big memory
>>>> for CMA and set coherent mask for dev, then dma_alloc and dma_mapping will not use the swiotlb until
>>>> the memory out of mask or swiotlb_force is enabled.
>>>>
>>>> If I still understand uncorrectly, please inform me.
>>>>
>>>
>>> Please do not use CMA to work around the problem, but fix the underlying bug
>>> instead.
>>>
>>> The driver should call 'dma_set_mask_and_coherent()' with the appropriate
>>> dma mask, and check whether that succeeded. However, the code implementing
>>> dma_set_mask_and_coherent on arm64 also needs to be changed to look up
>>> the dma-ranges property (see of_dma_configure()), and check if the mask
>>> is possible.
>>>
>> The dma_pfn_offset looks only support arm32, but my platform is aarch64 and I check the latest kernel version, 
>> I think the dma-rangs still could not work for aarch64, so maybe we should add dma_pfn_offset for aarch64 first.
>>
> 
> I didn't mean the dma_pfn_offset. The problem is that the of_dma_configure
> code currently doesn't look at the mask. As I explained in my reply to
> Catalin, it should set the mask to the size of the dma-ranges if that is
> 32-bit or smaller, and dma_set_mask should look at the same dma-ranges
> property to decide what to set the mask to when a driver asks for a
> mask larger than 64-bit.
> 
> 	Arnd
> 
ok, I think the your reply to catalin is clear, I got it, add a appropriate mask for the dev is
reasonable, I think it should be fixed later.

But in my case, if I don't use the DMA_CMA, the dma_alloc_coherent should use the swiotlb directly which maximum is 16M,
so unless I use the kmalloc otherwise I have no better idea for that.

Regards
Ding 

> .
> 


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