linux-kernel - Re: [PATCH 14/28] nios2: DMA mapping API

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Date:	Fri, 25 Apr 2014 18:13:31 +0800
From:	Ley Foon Tan <lftan@...era.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	cltang@...esourcery.com
Subject: Re: [PATCH 14/28] nios2: DMA mapping API

On Tue, Apr 22, 2014 at 9:52 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Friday 18 April 2014, Ley Foon Tan wrote:
>
>> +static inline int dma_supported(struct device *dev, u64 mask)
>> +{
>> +     /* we fall back to GFP_DMA when the mask isn't all 1s,
>> +      * so we can't guarantee allocations that must be
>> +      * within a tighter range than GFP_DMA.
>> +      */
>> +     if (mask < 0x00ffffff)
>> +             return 0;
>> +
>> +     return 1;
>> +}
>
>> +void *dma_alloc_coherent(struct device *dev, size_t size,
>> +                         dma_addr_t *dma_handle, gfp_t gfp)
>> +{
>> +     void *ret;
>> +
>> +     /* ignore region specifiers */
>> +     gfp &= ~(__GFP_DMA | __GFP_HIGHMEM);
>> +
>> +     /* optimized page clearing */
>> +     gfp |= __GFP_ZERO;
>> +
>> +     if (dev == NULL || (dev->coherent_dma_mask < 0xffffffff))
>> +             gfp |= GFP_DMA;
>
> What is the significance of ZONE_DMA on this architecture?
>
> Do you actually have DMA masters with a 0x00ffffff mask?
Actually, nios2 doesn't have DMA master with 0x00ffffff mask. I will
change it to return 1, same as some other architectures
implementation.
And the ZONE_DMA stuff will remove as well, it shouldn't have ZONE_DMA
limitation.
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