linux-kernel - Re: [PATCH v2 2/3] MIPS: Loongson: Add DMA support for 7A1000

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Date:   Thu, 26 Mar 2020 10:44:06 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH v2 2/3] MIPS: Loongson: Add DMA support for 7A1000

On 03/25/2020 09:27 PM, Christoph Hellwig wrote:
> On Mon, Mar 23, 2020 at 10:59:14AM +0800, Tiezhu Yang wrote:
>> Implement __phys_to_dma() and __dma_to_phys() according to the
>> node id offset in the 7A1000 DMA route config register.
> Can you please try to just use the dma_pfn_offset field in struct device
> for all loongson platforms?  I'm pretty sure I asked for that last time
> around..

Oh, sorry, I don't quite understand what you mean last time.

Do you mean use the default implementation in include/linux/dma-direct.h
when CONFIG_ARCH_HAS_PHYS_TO_DMA is not set?

#ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA
#include <asm/dma-direct.h>
#else
static inline dma_addr_t __phys_to_dma(struct device *dev, phys_addr_t 
paddr)
{
         dma_addr_t dev_addr = (dma_addr_t)paddr;

         return dev_addr - ((dma_addr_t)dev->dma_pfn_offset << PAGE_SHIFT);
}

static inline phys_addr_t __dma_to_phys(struct device *dev, dma_addr_t 
dev_addr)
{
         phys_addr_t paddr = (phys_addr_t)dev_addr;

         return paddr + ((phys_addr_t)dev->dma_pfn_offset << PAGE_SHIFT);
}
#endif /* !CONFIG_ARCH_HAS_PHYS_TO_DMA */

If so, I will verify it used with the AMD RS780E and Loongson 7A1000 
bridge chip.

Thanks,

Tiezhu Yang