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Date: Tue, 17 Dec 2013 12:57:42 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Stefano Panella <stefano.panella@...rix.com>, x86@...nel.org,
bhelgaas@...gle.com, joro@...tes.org,
iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
shuah.khan@...com, akpm@...ux-foundation.org
Cc: gregkh@...uxfoundation.org, maarten.lankhorst@...onical.com,
mingo@...nel.org, stefano.stabellini@...citrix.com,
zoltan.kiss@...rix.com, joe@...ches.com,
linux-kernel@...r.kernel.org, xen-devel@...ts.xen.org
Subject: Re: [RFC] dma-mapping: dma_alloc_coherent_mask return dma_addr_t
On Tue, Dec 10, 2013 at 04:05:37PM +0000, Stefano Panella wrote:
> When running a 32bit kernel there are still some pci devices
> capable of 64bit addressing (eg. sound/pci/hda/hda_intel.c)
>
> If these drivers are setting:
>
> dev->coherent_dma_mask = 0xFFFFFFFFFFFFFFFF
>
> why dma_alloc_coherent_mask is returning unsigned long instead
> of dma_addr_t resulting in truncation of the dma_mask to 32bit
> if running a 32bit kernel?
Ooops.
>
> There are some examples where the dma_alloc_coherent running
> 32bit kernel can return a machine address bigger than 32bit.
>
> This can be true in particular if running the 32bit kernel as a
> pv dom0 under the Xen Hypervisor or PAE on bare metal.
>
> In both cases it would be good if dma_alloc_coherent could return
> a machine address bigger than 32bit so more constrained 32bit address
> space could be used by devices not 64bit capable.
>
> I am proposing this patch to eliminate this limitation but I agree
> that there might be some more reasons to do it in the current way of
> which I am not awere.
>
> This is why I am just asking for a RFC.
>
> The current patch apply to v3.13-rc3-74-g6c843f5
This looks to be already done for other parts of the kernel, see:
commit 364230b9952143eb2062dc071e919fb751540ae8
Author: Rob Herring <rob.herring@...xeda.com>
Date: Thu Aug 1 15:29:29 2013 -0500
ARM: use phys_addr_t for DMA zone sizes
commit 6d7d5da7d75c6df676c8b72d32b02ff024438f0c
Author: Magnus Damm <damm@...nsource.se>
Date: Tue Oct 22 17:59:54 2013 +0100
ARM: 7864/1: Handle 64-bit memory in case of 32-bit phys_addr_t
mmit dbd3fc3345390a989a033427aa915a0dfb62149f
Author: Bjorn Helgaas <bhelgaas@...gle.com>
Date: Mon Dec 10 11:24:42 2012 -0700
PCI: Use phys_addr_t for physical ROM address
commit 7e6735c3578e76c270a2797225a4214176ba13ef
Author: Cyril Chemparathy <cyril@...com>
Date: Wed Sep 12 14:05:58 2012 -0400
/dev/mem: use phys_addr_t for physical addresses
Where the phys_addr_t is used instead of unsigned long. This is
doing it for the dma_addr_t.
So I think this is the correct thing to do. We should CC more
people thought.
>
> Signed-off-by: Stefano Panella <stefano.panella@...rix.com>
> ---
> Documentation/DMA-API.txt | 5 ++---
> arch/x86/include/asm/dma-mapping.h | 8 ++++----
> arch/x86/kernel/pci-dma.c | 2 +-
> drivers/xen/swiotlb-xen.c | 6 +++---
> 4 files changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
> index e865279..483458b 100644
> --- a/Documentation/DMA-API.txt
> +++ b/Documentation/DMA-API.txt
> @@ -33,9 +33,8 @@ to make sure to flush the processor's write buffers before telling
> devices to read that memory.)
>
> This routine allocates a region of <size> bytes of consistent memory.
> -It also returns a <dma_handle> which may be cast to an unsigned
> -integer the same width as the bus and used as the physical address
> -base of the region.
> +It also returns a <dma_handle> which should be used as the physical
> +address base of the region.
>
> Returns: a pointer to the allocated region (in the processor's virtual
> address space) or NULL if the allocation failed.
> diff --git a/arch/x86/include/asm/dma-mapping.h b/arch/x86/include/asm/dma-mapping.h
> index 808dae6..6357810 100644
> --- a/arch/x86/include/asm/dma-mapping.h
> +++ b/arch/x86/include/asm/dma-mapping.h
> @@ -100,10 +100,10 @@ dma_cache_sync(struct device *dev, void *vaddr, size_t size,
> flush_write_buffers();
> }
>
> -static inline unsigned long dma_alloc_coherent_mask(struct device *dev,
> - gfp_t gfp)
> +static inline dma_addr_t dma_alloc_coherent_mask(struct device *dev,
> + gfp_t gfp)
> {
> - unsigned long dma_mask = 0;
> + dma_addr_t dma_mask = 0;
>
> dma_mask = dev->coherent_dma_mask;
> if (!dma_mask)
> @@ -114,7 +114,7 @@ static inline unsigned long dma_alloc_coherent_mask(struct device *dev,
>
> static inline gfp_t dma_alloc_coherent_gfp_flags(struct device *dev, gfp_t gfp)
> {
> - unsigned long dma_mask = dma_alloc_coherent_mask(dev, gfp);
> + dma_addr_t dma_mask = dma_alloc_coherent_mask(dev, gfp);
>
> if (dma_mask <= DMA_BIT_MASK(24))
> gfp |= GFP_DMA;
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index 872079a..a061f7b 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -90,7 +90,7 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size,
> dma_addr_t *dma_addr, gfp_t flag,
> struct dma_attrs *attrs)
> {
> - unsigned long dma_mask;
> + dma_addr_t dma_mask;
> struct page *page;
> unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> dma_addr_t addr;
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 1eac073..6f75599 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -54,10 +54,10 @@
> */
>
> #ifndef CONFIG_X86
> -static unsigned long dma_alloc_coherent_mask(struct device *dev,
> - gfp_t gfp)
> +static dma_addr_t dma_alloc_coherent_mask(struct device *dev,
> + gfp_t gfp)
> {
> - unsigned long dma_mask = 0;
> + dma_addr_t dma_mask = 0;
>
> dma_mask = dev->coherent_dma_mask;
> if (!dma_mask)
> --
> 1.7.9.5
>
--
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