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Re: [PATCH V19 09/13] MIPS: Loongson: Add swiotlb to support All-Memory

To: "陈华才" <chenhc@lemote.com>
Subject: Re: [PATCH V19 09/13] MIPS: Loongson: Add swiotlb to support All-Memory DMA
From: Aurelien Jarno <aurelien@aurel32.net>
Date: Wed, 19 Feb 2014 22:39:20 +0100
Cc: Ralf Baechle <ralf@linux-mips.org>, John Crispin <john@phrozen.org>, "Steven J. Hill" <steven.hill@imgtec.com>, linux-mips@linux-mips.org, Fuxin Zhang <zhangfx@lemote.com>, Zhangjin Wu <wuzhangjin@gmail.com>, Hongliang Tao <taohl@lemote.com>, Hua Yan <yanh@lemote.com>
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References: <1392537690-5961-1-git-send-email-chenhc@lemote.com> <1392537690-5961-10-git-send-email-chenhc@lemote.com> <20140216211206.GA491@hall.aurel32.net> <c4cab01ceda4c21c8d9c7e471edfe000.squirrel@mail.lemote.com>
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On Mon, Feb 17, 2014 at 01:41:49PM +0800, "陈华才" wrote:
> > On Sun, Feb 16, 2014 at 04:01:26PM +0800, Huacai Chen wrote:
> >> Loongson doesn't support DMA address above 4GB traditionally. If memory
> >> is more than 4GB, CONFIG_SWIOTLB and ZONE_DMA32 should be selected. In
> >> this way, DMA pages are allocated below 4GB preferably. However, if low
> >> memory is not enough, high pages are allocated and swiotlb is used for
> >> bouncing.
> >>
> >> Moreover, we provide a platform-specific dma_map_ops::set_dma_mask() to
> >> set a device's dma_mask and coherent_dma_mask. We use these masks to
> >> distinguishes an allocated page can be used for DMA directly, or need
> >> swiotlb to bounce.
> >>
> >> Recently, we found that 32-bit DMA isn't a hardware bug, but a hardware
> >> configuration issue. So, latest firmware has enable the DMA support as
> >> high as 40-bit. To support all-memory DMA for all devices (besides the
> >> Loongson platform limit, there are still some devices have their own
> >> DMA32 limit), and also to be compatible with old firmware, we keep use
> >> swiotlb.
> >>
> >> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> >> Signed-off-by: Hongliang Tao <taohl@lemote.com>
> >> Signed-off-by: Hua Yan <yanh@lemote.com>
> >> Tested-by: Alex Smith <alex.smith@imgtec.com>
> >> Reviewed-by: Alex Smith <alex.smith@imgtec.com>
> >> ---
> >>  arch/mips/include/asm/dma-mapping.h                |    5 +
> >>  .../mips/include/asm/mach-loongson/dma-coherence.h |   22 +++-
> >>  arch/mips/loongson/common/Makefile                 |    5 +
> >>  arch/mips/loongson/common/dma-swiotlb.c            |  136
> >> ++++++++++++++++++++
> >>  4 files changed, 167 insertions(+), 1 deletions(-)
> >>  create mode 100644 arch/mips/loongson/common/dma-swiotlb.c
> >>
> >> diff --git a/arch/mips/include/asm/dma-mapping.h
> >> b/arch/mips/include/asm/dma-mapping.h
> >> index 84238c5..06412aa 100644
> >> --- a/arch/mips/include/asm/dma-mapping.h
> >> +++ b/arch/mips/include/asm/dma-mapping.h
> >> @@ -49,9 +49,14 @@ static inline int dma_mapping_error(struct device
> >> *dev, u64 mask)
> >>  static inline int
> >>  dma_set_mask(struct device *dev, u64 mask)
> >>  {
> >> +  struct dma_map_ops *ops = get_dma_ops(dev);
> >> +
> >>    if(!dev->dma_mask || !dma_supported(dev, mask))
> >>            return -EIO;
> >>
> >> +  if (ops->set_dma_mask)
> >> +          return ops->set_dma_mask(dev, mask);
> >> +
> >>    *dev->dma_mask = mask;
> >>
> >>    return 0;
> >> diff --git a/arch/mips/include/asm/mach-loongson/dma-coherence.h
> >> b/arch/mips/include/asm/mach-loongson/dma-coherence.h
> >> index aeb2c05..6a90275 100644
> >> --- a/arch/mips/include/asm/mach-loongson/dma-coherence.h
> >> +++ b/arch/mips/include/asm/mach-loongson/dma-coherence.h
> >> @@ -11,24 +11,40 @@
> >>  #ifndef __ASM_MACH_LOONGSON_DMA_COHERENCE_H
> >>  #define __ASM_MACH_LOONGSON_DMA_COHERENCE_H
> >>
> >> +#ifdef CONFIG_SWIOTLB
> >> +#include <linux/swiotlb.h>
> >> +#endif
> >> +
> >>  struct device;
> >>
> >> +extern dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr);
> >> +extern phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr);
> >>  static inline dma_addr_t plat_map_dma_mem(struct device *dev, void
> >> *addr,
> >>                                      size_t size)
> >>  {
> >> +#ifdef CONFIG_CPU_LOONGSON3
> >> +  return virt_to_phys(addr);
> >> +#else
> >>    return virt_to_phys(addr) | 0x80000000;
> >> +#endif
> >>  }
> >>
> >>  static inline dma_addr_t plat_map_dma_mem_page(struct device *dev,
> >>                                           struct page *page)
> >>  {
> >> +#ifdef CONFIG_CPU_LOONGSON3
> >> +  return page_to_phys(page);
> >> +#else
> >>    return page_to_phys(page) | 0x80000000;
> >> +#endif
> >>  }
> >>
> >>  static inline unsigned long plat_dma_addr_to_phys(struct device *dev,
> >>    dma_addr_t dma_addr)
> >>  {
> >> -#if defined(CONFIG_CPU_LOONGSON2F) && defined(CONFIG_64BIT)
> >> +#if defined(CONFIG_CPU_LOONGSON3) && defined(CONFIG_64BIT)
> >> +  return dma_addr;
> >> +#elif defined(CONFIG_CPU_LOONGSON2F) && defined(CONFIG_64BIT)
> >>    return (dma_addr > 0x8fffffff) ? dma_addr : (dma_addr & 0x0fffffff);
> >>  #else
> >>    return dma_addr & 0x7fffffff;
> >> @@ -55,7 +71,11 @@ static inline int plat_dma_supported(struct device
> >> *dev, u64 mask)
> >>
> >>  static inline int plat_device_is_coherent(struct device *dev)
> >>  {
> >> +#ifdef CONFIG_DMA_NONCOHERENT
> >>    return 0;
> >> +#else
> >> +  return 1;
> >> +#endif /* CONFIG_DMA_NONCOHERENT */
> >>  }
> >>
> >>  #endif /* __ASM_MACH_LOONGSON_DMA_COHERENCE_H */
> >> diff --git a/arch/mips/loongson/common/Makefile
> >> b/arch/mips/loongson/common/Makefile
> >> index 9e4484c..0bb9cc9 100644
> >> --- a/arch/mips/loongson/common/Makefile
> >> +++ b/arch/mips/loongson/common/Makefile
> >> @@ -26,3 +26,8 @@ obj-$(CONFIG_CS5536) += cs5536/
> >>  #
> >>
> >>  obj-$(CONFIG_LOONGSON_SUSPEND) += pm.o
> >> +
> >> +#
> >> +# Big Memory (SWIOTLB) Support
> >> +#
> >> +obj-$(CONFIG_SWIOTLB) += dma-swiotlb.o
> >> diff --git a/arch/mips/loongson/common/dma-swiotlb.c
> >> b/arch/mips/loongson/common/dma-swiotlb.c
> >> new file mode 100644
> >> index 0000000..c2be01f
> >> --- /dev/null
> >> +++ b/arch/mips/loongson/common/dma-swiotlb.c
> >> @@ -0,0 +1,136 @@
> >> +#include <linux/mm.h>
> >> +#include <linux/init.h>
> >> +#include <linux/dma-mapping.h>
> >> +#include <linux/scatterlist.h>
> >> +#include <linux/swiotlb.h>
> >> +#include <linux/bootmem.h>
> >> +
> >> +#include <asm/bootinfo.h>
> >> +#include <boot_param.h>
> >> +#include <dma-coherence.h>
> >> +
> >> +static void *loongson_dma_alloc_coherent(struct device *dev, size_t
> >> size,
> >> +          dma_addr_t *dma_handle, gfp_t gfp, struct dma_attrs *attrs)
> >> +{
> >> +  void *ret;
> >> +
> >> +  if (dma_alloc_from_coherent(dev, size, dma_handle, &ret))
> >> +          return ret;
> >> +
> >> +  /* ignore region specifiers */
> >> +  gfp &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM);
> >> +
> >> +#ifdef CONFIG_ISA
> >> +  if (dev == NULL)
> >> +          gfp |= __GFP_DMA;
> >> +  else
> >> +#endif
> >> +#ifdef CONFIG_ZONE_DMA
> >> +  if (dev->coherent_dma_mask < DMA_BIT_MASK(32))
> >> +          gfp |= __GFP_DMA;
> >> +  else
> >> +#endif
> >> +#ifdef CONFIG_ZONE_DMA32
> >> +  if (dev->coherent_dma_mask < DMA_BIT_MASK(40))
> >> +          gfp |= __GFP_DMA32;
> >> +  else
> >
> > I think the same logic as in loongson_dma_set_mask should be used there,
> > so that the bounce buffer is not used when it is possible to directly
> > allocate the memory correctly. Something like this should work:
> It seems like that we needn't to do so. Assume that loongson_sysconf.
> dma_mask_bits is 41 and a device's dma_mask is 40. DMA32 zone is very
> limited, but all physical memory addresses are below 40bit. If using
>  __GFP_DMA32, swiotlb is probably needed because DMA32 zone is exhausted
> by those dma32 devices; but if not using __GFP_DMA32, swiotlb isn't need
> completely.

I don't agree. If the DMA32 zone is full, then the memory will be
allocated in the normal zone. swiotlb is then only used in the case the
allocated DMA memory is outside of the dma_mask_bits area.

Also how the value 40 from the current code has been chosen? If a
device's dma_mask is 39, DMA32 will be exhausted by those dma32
devices...

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net

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