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Date: Tue, 6 Aug 2013 11:48:04 -0600
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Chris Metcalf <cmetcalf@...era.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
Myron Stowe <myron.stowe@...hat.com>,
adam radford <aradford@...il.com>
Subject: Re: [PATCH v2] tile: support LSI MEGARAID SAS HBA hybrid dma_ops
[+cc Myron, Adam]
On Fri, Aug 2, 2013 at 10:24 AM, Chris Metcalf <cmetcalf@...era.com> wrote:
> The LSI MEGARAID SAS HBA suffers from the problem where it can do
> 64-bit DMA to streaming buffers but not to consistent buffers.
> In other words, 64-bit DMA is used for disk data transfers and 32-bit
> DMA must be used for control message transfers.
Is this related at all to the make_local_pdev() hacks in megaraid.c?
The intent there seems to be to use a 32-bit DMA mask for certain
transactions and a 64-bit mask for others. But I think it's actually
broken, because the implementation changes the mask to 32-bit for
*all* future transactions, not just the one using make_local_pdev().
> According to LSI,
> the firmware is not fully functional yet. This change implements a
> kind of hybrid dma_ops to support this.
>
> Note that on most other platforms, the 64-bit DMA addressing space is the
> same as the 32-bit DMA space and they overlap the physical memory space.
> No special arrangement is needed to support this kind of mixed DMA
> capability. On TILE-Gx, the 64-bit DMA space is completely separate
> from the 32-bit DMA space.
Help me understand what's going on here. My understanding is that on
typical systems, the 32-bit DMA space is a subset of the 64-bit DMA
space. In conventional PCI, "a master that supports 64-bit addressing
must generate a SAC, instead of a DAC, when the upper 32 bits of the
address are zero" (PCI spec r3.0, sec 3.9). PCIe doesn't have
SAC/DAC, but it has both 32-bit and 64-bit address headers and has a
similar requirement: "For Addresses below 4GB, Requesters must use the
32-bit format" (PCIe spec r3.0, sec 2.2.4.1).
Those imply to me that the 0-4GB region of the 64-bit DMA space must
be identical to the 0-4GB 32-bit DMA space, and in fact, the receiver
of a transaction shouldn't be able to distinguish them.
But it sounds like something's different on TILE-Gx? Does it
translate bus addresses to physical memory addresses based on the type
of the transaction (SAC vs DAC, or 32-bit vs 64-bit header) in
addition to the address? Even if it does, the spec doesn't allow a
DAC cycle or a 64-bit header where the 32 high-order bits are zero, so
it shouldn't matter.
Bjorn
> Due to the use of the IOMMU, the 64-bit DMA
> space doesn't overlap the physical memory space. On the other hand,
> the 32-bit DMA space overlaps the physical memory space under 4GB.
> The separate address spaces make it necessary to have separate dma_ops.
>
> Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
> ---
> arch/tile/include/asm/dma-mapping.h | 10 +++++++---
> arch/tile/kernel/pci-dma.c | 40 ++++++++++++++++++++++++++++---------
> 2 files changed, 38 insertions(+), 12 deletions(-)
>
> diff --git a/arch/tile/include/asm/dma-mapping.h b/arch/tile/include/asm/dma-mapping.h
> index f2ff191..4a60059 100644
> --- a/arch/tile/include/asm/dma-mapping.h
> +++ b/arch/tile/include/asm/dma-mapping.h
> @@ -23,6 +23,7 @@
> extern struct dma_map_ops *tile_dma_map_ops;
> extern struct dma_map_ops *gx_pci_dma_map_ops;
> extern struct dma_map_ops *gx_legacy_pci_dma_map_ops;
> +extern struct dma_map_ops *gx_hybrid_pci_dma_map_ops;
>
> static inline struct dma_map_ops *get_dma_ops(struct device *dev)
> {
> @@ -44,12 +45,12 @@ static inline void set_dma_offset(struct device *dev, dma_addr_t off)
>
> static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr)
> {
> - return paddr + get_dma_offset(dev);
> + return paddr;
> }
>
> static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr)
> {
> - return daddr - get_dma_offset(dev);
> + return daddr;
> }
>
> static inline void dma_mark_clean(void *addr, size_t size) {}
> @@ -88,7 +89,10 @@ dma_set_mask(struct device *dev, u64 mask)
> struct dma_map_ops *dma_ops = get_dma_ops(dev);
>
> /* Handle legacy PCI devices with limited memory addressability. */
> - if ((dma_ops == gx_pci_dma_map_ops) && (mask <= DMA_BIT_MASK(32))) {
> + if ((dma_ops == gx_pci_dma_map_ops ||
> + dma_ops == gx_hybrid_pci_dma_map_ops ||
> + dma_ops == gx_legacy_pci_dma_map_ops) &&
> + (mask <= DMA_BIT_MASK(32))) {
> set_dma_ops(dev, gx_legacy_pci_dma_map_ops);
> set_dma_offset(dev, 0);
> if (mask > dev->archdata.max_direct_dma_addr)
> diff --git a/arch/tile/kernel/pci-dma.c b/arch/tile/kernel/pci-dma.c
> index b9fe80e..7e22e73 100644
> --- a/arch/tile/kernel/pci-dma.c
> +++ b/arch/tile/kernel/pci-dma.c
> @@ -357,7 +357,7 @@ static void *tile_pci_dma_alloc_coherent(struct device *dev, size_t size,
>
> addr = page_to_phys(pg);
>
> - *dma_handle = phys_to_dma(dev, addr);
> + *dma_handle = addr + get_dma_offset(dev);
>
> return page_address(pg);
> }
> @@ -387,7 +387,7 @@ static int tile_pci_dma_map_sg(struct device *dev, struct scatterlist *sglist,
> sg->dma_address = sg_phys(sg);
> __dma_prep_pa_range(sg->dma_address, sg->length, direction);
>
> - sg->dma_address = phys_to_dma(dev, sg->dma_address);
> + sg->dma_address = sg->dma_address + get_dma_offset(dev);
> #ifdef CONFIG_NEED_SG_DMA_LENGTH
> sg->dma_length = sg->length;
> #endif
> @@ -422,7 +422,7 @@ static dma_addr_t tile_pci_dma_map_page(struct device *dev, struct page *page,
> BUG_ON(offset + size > PAGE_SIZE);
> __dma_prep_page(page, offset, size, direction);
>
> - return phys_to_dma(dev, page_to_pa(page) + offset);
> + return page_to_pa(page) + offset + get_dma_offset(dev);
> }
>
> static void tile_pci_dma_unmap_page(struct device *dev, dma_addr_t dma_address,
> @@ -432,7 +432,7 @@ static void tile_pci_dma_unmap_page(struct device *dev, dma_addr_t dma_address,
> {
> BUG_ON(!valid_dma_direction(direction));
>
> - dma_address = dma_to_phys(dev, dma_address);
> + dma_address -= get_dma_offset(dev);
>
> __dma_complete_page(pfn_to_page(PFN_DOWN(dma_address)),
> dma_address & PAGE_OFFSET, size, direction);
> @@ -445,7 +445,7 @@ static void tile_pci_dma_sync_single_for_cpu(struct device *dev,
> {
> BUG_ON(!valid_dma_direction(direction));
>
> - dma_handle = dma_to_phys(dev, dma_handle);
> + dma_handle -= get_dma_offset(dev);
>
> __dma_complete_pa_range(dma_handle, size, direction);
> }
> @@ -456,7 +456,7 @@ static void tile_pci_dma_sync_single_for_device(struct device *dev,
> enum dma_data_direction
> direction)
> {
> - dma_handle = dma_to_phys(dev, dma_handle);
> + dma_handle -= get_dma_offset(dev);
>
> __dma_prep_pa_range(dma_handle, size, direction);
> }
> @@ -558,21 +558,43 @@ static struct dma_map_ops pci_swiotlb_dma_ops = {
> .mapping_error = swiotlb_dma_mapping_error,
> };
>
> +static struct dma_map_ops pci_hybrid_dma_ops = {
> + .alloc = tile_swiotlb_alloc_coherent,
> + .free = tile_swiotlb_free_coherent,
> + .map_page = tile_pci_dma_map_page,
> + .unmap_page = tile_pci_dma_unmap_page,
> + .map_sg = tile_pci_dma_map_sg,
> + .unmap_sg = tile_pci_dma_unmap_sg,
> + .sync_single_for_cpu = tile_pci_dma_sync_single_for_cpu,
> + .sync_single_for_device = tile_pci_dma_sync_single_for_device,
> + .sync_sg_for_cpu = tile_pci_dma_sync_sg_for_cpu,
> + .sync_sg_for_device = tile_pci_dma_sync_sg_for_device,
> + .mapping_error = tile_pci_dma_mapping_error,
> + .dma_supported = tile_pci_dma_supported
> +};
> +
> struct dma_map_ops *gx_legacy_pci_dma_map_ops = &pci_swiotlb_dma_ops;
> +struct dma_map_ops *gx_hybrid_pci_dma_map_ops = &pci_hybrid_dma_ops;
> #else
> struct dma_map_ops *gx_legacy_pci_dma_map_ops;
> +struct dma_map_ops *gx_hybrid_pci_dma_map_ops;
> #endif
> EXPORT_SYMBOL(gx_legacy_pci_dma_map_ops);
> +EXPORT_SYMBOL(gx_hybrid_pci_dma_map_ops);
>
> #ifdef CONFIG_ARCH_HAS_DMA_SET_COHERENT_MASK
> int dma_set_coherent_mask(struct device *dev, u64 mask)
> {
> struct dma_map_ops *dma_ops = get_dma_ops(dev);
>
> - /* Handle legacy PCI devices with limited memory addressability. */
> - if (((dma_ops == gx_pci_dma_map_ops) ||
> - (dma_ops == gx_legacy_pci_dma_map_ops)) &&
> + /* Handle hybrid PCI devices with limited memory addressability. */
> + if ((dma_ops == gx_pci_dma_map_ops ||
> + dma_ops == gx_hybrid_pci_dma_map_ops ||
> + dma_ops == gx_legacy_pci_dma_map_ops) &&
> (mask <= DMA_BIT_MASK(32))) {
> + if (dma_ops == gx_pci_dma_map_ops)
> + set_dma_ops(dev, gx_hybrid_pci_dma_map_ops);
> +
> if (mask > dev->archdata.max_direct_dma_addr)
> mask = dev->archdata.max_direct_dma_addr;
> }
> --
> 1.8.3.1
>
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