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Re: [PATCH V5 09/18] MIPS: Loongson: Add swiotlb to support big memory (

To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH V5 09/18] MIPS: Loongson: Add swiotlb to support big memory (>4GB).
From: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 15 Aug 2012 22:24:36 +0200
Cc: Huacai Chen <chenhuacai@gmail.com>, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, Fuxin Zhang <zhangfx@lemote.com>, Zhangjin Wu <wuzhangjin@gmail.com>, Huacai Chen <chenhc@lemote.com>, Hongliang Tao <taohl@lemote.com>, Hua Yan <yanh@lemote.com>
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On Mon, Aug 13, 2012 at 01:54:47PM -0400, Konrad Rzeszutek Wilk wrote:

> > +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_ZONE_DMA
> > +   if (dev == NULL)
> > +           gfp |= __GFP_DMA;
> 
> When would this happen? dev == NULL?

A legacy (ISA) device driver.  Some of the Loongsons have some kind of
southbridge which incorporates legacy devices though of the top of my
head I'm not sure which if any of these are actually being used.  Huacai?

> > +   else if (dev->coherent_dma_mask <= DMA_BIT_MASK(24))
> > +           gfp |= __GFP_DMA;
> > +   else
> > +#endif
> > +#ifdef CONFIG_ZONE_DMA32
> > +   if (dev->coherent_dma_mask <= DMA_BIT_MASK(32))
> > +           gfp |= __GFP_DMA32;
> > +   else
> 
> Why the 'else'
> > +#endif
> > +   ;
> 
> why?
> > +   gfp |= __GFP_NORETRY;
> > +
> > +   ret = swiotlb_alloc_coherent(dev, size, dma_handle, gfp);
> > +   mb();
> 
> Why the 'mb()' ? Can you just do
>       return swiotlb_alloc_coherent(...) 
> 
> > +   return ret;
> > +}
> > +
> > +static void loongson_dma_free_coherent(struct device *dev, size_t size,
> > +                           void *vaddr, dma_addr_t dma_handle, struct 
> > dma_attrs *attrs)
> > +{
> > +   int order = get_order(size);
> > +
> > +   if (dma_release_from_coherent(dev, order, vaddr))
> > +           return;
> > +
> > +   swiotlb_free_coherent(dev, size, vaddr, dma_handle);
> > +}
> > +
> > +static dma_addr_t loongson_dma_map_page(struct device *dev, struct page 
> > *page,
> > +                           unsigned long offset, size_t size,
> > +                           enum dma_data_direction dir,
> > +                           struct dma_attrs *attrs)
> > +{
> > +   dma_addr_t daddr = swiotlb_map_page(dev, page, offset, size,
> > +                                   dir, attrs);
> > +   mb();
> 
> Please do 'return swiotlb_map_page(..)'..
> 
> But if you are doing that why don't you just set the dma_ops.map_page = 
> swiotlb_map_page
> ?
> 
> 
> > +   return daddr;
> > +}
> > +
> > +static int loongson_dma_map_sg(struct device *dev, struct scatterlist *sg,
> > +                           int nents, enum dma_data_direction dir,
> > +                           struct dma_attrs *attrs)
> > +{
> > +   int r = swiotlb_map_sg_attrs(dev, sg, nents, dir, NULL);
> > +   mb();
> > +
> > +   return r;
> > +}
> > +
> > +static void loongson_dma_sync_single_for_device(struct device *dev,
> > +                           dma_addr_t dma_handle, size_t size,
> > +                           enum dma_data_direction dir)
> > +{
> > +   swiotlb_sync_single_for_device(dev, dma_handle, size, dir);
> > +   mb();
> > +}
> > +
> > +static void loongson_dma_sync_sg_for_device(struct device *dev,
> > +                           struct scatterlist *sg, int nents,
> > +                           enum dma_data_direction dir)
> > +{
> > +   swiotlb_sync_sg_for_device(dev, sg, nents, dir);
> > +   mb();
> > +}
> > +
> 
> I am not really sure why you have these extra functions, when you could
> just modify the dma_ops to point to the swiotlb ones
> 
> > +static dma_addr_t loongson_unity_phys_to_dma(struct device *dev, 
> > phys_addr_t paddr)
> > +{
> > +   return (paddr < 0x10000000) ?
> > +                   (paddr | 0x0000000080000000) : paddr;
> > +}
> > +
> > +static phys_addr_t loongson_unity_dma_to_phys(struct device *dev, 
> > dma_addr_t daddr)
> > +{
> > +   return (daddr < 0x90000000 && daddr >= 0x80000000) ?
> > +                   (daddr & 0x0fffffff) : daddr;
> > +}
> > +
> > +struct loongson_dma_map_ops {
> > +   struct dma_map_ops dma_map_ops;
> > +   dma_addr_t (*phys_to_dma)(struct device *dev, phys_addr_t paddr);
> > +   phys_addr_t (*dma_to_phys)(struct device *dev, dma_addr_t daddr);
> > +};
> > +
> > +dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr)
> > +{
> > +   struct loongson_dma_map_ops *ops = container_of(get_dma_ops(dev),
> > +                                   struct loongson_dma_map_ops, 
> > dma_map_ops);
> > +
> > +   return ops->phys_to_dma(dev, paddr);
> > +}
> > +
> > +phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr)
> > +{
> > +   struct loongson_dma_map_ops *ops = container_of(get_dma_ops(dev),
> > +                                   struct loongson_dma_map_ops, 
> > dma_map_ops);
> > +
> > +   return ops->dma_to_phys(dev, daddr);
> > +}
> > +
> > +static int loongson_dma_set_mask(struct device *dev, u64 mask)
> > +{
> > +   /* Loongson doesn't support DMA above 32-bit */
> > +   if (mask > DMA_BIT_MASK(32))
> > +           return -EIO;
> > +
> > +   *dev->dma_mask = mask;
> > +
> > +   return 0;
> > +}
> > +
> > +static struct loongson_dma_map_ops loongson_linear_dma_map_ops = {
> > +   .dma_map_ops = {
> > +           .alloc = loongson_dma_alloc_coherent,
> > +           .free = loongson_dma_free_coherent,
> > +           .map_page = loongson_dma_map_page,
> 
> But why not 'swiotlb_map_page'?
> 
> > +           .unmap_page = swiotlb_unmap_page,
> > +           .map_sg = loongson_dma_map_sg,
> > +           .unmap_sg = swiotlb_unmap_sg_attrs,
> > +           .sync_single_for_cpu = swiotlb_sync_single_for_cpu,
> > +           .sync_single_for_device = loongson_dma_sync_single_for_device,
> > +           .sync_sg_for_cpu = swiotlb_sync_sg_for_cpu,
> > +           .sync_sg_for_device = loongson_dma_sync_sg_for_device,
> > +           .mapping_error = swiotlb_dma_mapping_error,
> > +           .dma_supported = swiotlb_dma_supported,
> > +           .set_dma_mask = loongson_dma_set_mask
> > +   },
> > +   .phys_to_dma = loongson_unity_phys_to_dma,
> > +   .dma_to_phys = loongson_unity_dma_to_phys
> 
> Why do you need these? I am not seeing it being used here by any external 
> code?
> 
> > +};
> > +
> > +void __init plat_swiotlb_setup(void)
> > +{
> > +   swiotlb_init(1);
> > +   mips_dma_map_ops = &loongson_linear_dma_map_ops.dma_map_ops;
> > +}
> > diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
> > index 3fab204..122f4f8 100644
> > --- a/arch/mips/mm/dma-default.c
> > +++ b/arch/mips/mm/dma-default.c
> > @@ -42,6 +42,13 @@ static inline int cpu_is_noncoherent_r10000(struct 
> > device *dev)
> >            current_cpu_type() == CPU_R12000);
> >  }
> >  
> > +static inline int cpu_is_noncoherent_loongson(struct device *dev)
> > +{
> > +   return !plat_device_is_coherent(dev) &&
> > +                   (current_cpu_type() == CPU_LOONGSON2 ||
> > +                    current_cpu_type() == CPU_LOONGSON3);
> > +}
> > +
> >  static gfp_t massage_gfp_flags(const struct device *dev, gfp_t gfp)
> >  {
> >     gfp_t dma_flag;
> > @@ -209,7 +216,7 @@ static inline void __dma_sync(struct page *page,
> >  static void mips_dma_unmap_page(struct device *dev, dma_addr_t dma_addr,
> >     size_t size, enum dma_data_direction direction, struct dma_attrs *attrs)
> >  {
> > -   if (cpu_is_noncoherent_r10000(dev))
> > +   if (cpu_is_noncoherent_r10000(dev) || cpu_is_noncoherent_loongson(dev))

Why this?  I hope you're not claiming the Loongson has the same very weird
behaviour as the R10000 in a non-coherent system.  No sane CPU should ...

  Ralf

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