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Message-ID: <c882430e-1dbd-df86-d686-0381dcaa668e@arm.com>
Date: Mon, 14 Jan 2019 13:12:33 +0000
From: Robin Murphy <robin.murphy@....com>
To: Christoph Hellwig <hch@....de>, Pawel Osciak <pawel@...iak.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Kyungmin Park <kyungmin.park@...sung.com>,
Niklas Söderlund
<niklas.soderlund+renesas@...natech.se>
Cc: Russell King <linux@...linux.org.uk>, linux-kernel@...r.kernel.org,
iommu@...ts.linux-foundation.org,
Mauro Carvalho Chehab <mchehab@...nel.org>,
linuxppc-dev@...ts.ozlabs.org,
linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 1/3] dma-mapping: remove the default map_resource
implementation
On 11/01/2019 18:17, Christoph Hellwig wrote:
> Just returning the physical address when not map_resource method is
> present is highly dangerous as it doesn't take any offset in the
> direct mapping into account and does the completely wrong thing for
> IOMMUs. Instead provide a proper implementation in the direct mapping
> code, and also wire it up for arm and powerpc.
Ignoring the offset was kind of intentional there, because at the time I
was primarily thinking about it in terms of the Keystone 2 platform
where the peripherals are all in the same place (0-2GB) in both the bus
and CPU physical address maps, and only the view of RAM differs between
the two (2-4GB vs. 32-34GB). However, on something like BCM283x, the
peripherals region is also offset from its bus address in the CPU view,
but at a *different* offset relative to that of RAM.
Fortunately, I'm not aware of any platform which has a DMA engine behind
an IOMMU (and thus *needs* to use dma_map_resource() to avoid said IOMMU
blocking the slave device register reads/writes) and also has any
nonzero offsets, and AFAIK the IOMMU-less platforms above aren't using
dma_map_resource() at all, so this change shouldn't actually break
anything, but I guess we have a bit of a problem making it truly generic
and robust :(
Is this perhaps another shove in the direction of overhauling
dma_pfn_offset into an arbitrary "DMA ranges" lookup table?
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
> arch/arm/mm/dma-mapping.c | 2 ++
> arch/powerpc/kernel/dma-swiotlb.c | 1 +
> arch/powerpc/kernel/dma.c | 1 +
> include/linux/dma-mapping.h | 12 +++++++-----
> kernel/dma/direct.c | 14 ++++++++++++++
> 5 files changed, 25 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index f1e2922e447c..3c8534904209 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -188,6 +188,7 @@ const struct dma_map_ops arm_dma_ops = {
> .unmap_page = arm_dma_unmap_page,
> .map_sg = arm_dma_map_sg,
> .unmap_sg = arm_dma_unmap_sg,
> + .map_resource = dma_direct_map_resource,
> .sync_single_for_cpu = arm_dma_sync_single_for_cpu,
> .sync_single_for_device = arm_dma_sync_single_for_device,
> .sync_sg_for_cpu = arm_dma_sync_sg_for_cpu,
> @@ -211,6 +212,7 @@ const struct dma_map_ops arm_coherent_dma_ops = {
> .get_sgtable = arm_dma_get_sgtable,
> .map_page = arm_coherent_dma_map_page,
> .map_sg = arm_dma_map_sg,
> + .map_resource = dma_direct_map_resource,
> .dma_supported = arm_dma_supported,
> };
> EXPORT_SYMBOL(arm_coherent_dma_ops);
> diff --git a/arch/powerpc/kernel/dma-swiotlb.c b/arch/powerpc/kernel/dma-swiotlb.c
> index 7d5fc9751622..fbb2506a414e 100644
> --- a/arch/powerpc/kernel/dma-swiotlb.c
> +++ b/arch/powerpc/kernel/dma-swiotlb.c
> @@ -55,6 +55,7 @@ const struct dma_map_ops powerpc_swiotlb_dma_ops = {
> .dma_supported = swiotlb_dma_supported,
> .map_page = dma_direct_map_page,
> .unmap_page = dma_direct_unmap_page,
> + .map_resource = dma_direct_map_resource,
> .sync_single_for_cpu = dma_direct_sync_single_for_cpu,
> .sync_single_for_device = dma_direct_sync_single_for_device,
> .sync_sg_for_cpu = dma_direct_sync_sg_for_cpu,
> diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c
> index b1903ebb2e9c..258b9e8ebb99 100644
> --- a/arch/powerpc/kernel/dma.c
> +++ b/arch/powerpc/kernel/dma.c
> @@ -273,6 +273,7 @@ const struct dma_map_ops dma_nommu_ops = {
> .dma_supported = dma_nommu_dma_supported,
> .map_page = dma_nommu_map_page,
> .unmap_page = dma_nommu_unmap_page,
> + .map_resource = dma_direct_map_resource,
> .get_required_mask = dma_nommu_get_required_mask,
> #ifdef CONFIG_NOT_COHERENT_CACHE
> .sync_single_for_cpu = dma_nommu_sync_single,
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index cef2127e1d70..d3087829a6df 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -208,6 +208,8 @@ dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
> unsigned long attrs);
> int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
> enum dma_data_direction dir, unsigned long attrs);
> +dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
> + size_t size, enum dma_data_direction dir, unsigned long attrs);
>
> #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
> defined(CONFIG_SWIOTLB)
> @@ -346,19 +348,19 @@ static inline dma_addr_t dma_map_resource(struct device *dev,
> unsigned long attrs)
> {
> const struct dma_map_ops *ops = get_dma_ops(dev);
> - dma_addr_t addr;
> + dma_addr_t addr = DMA_MAPPING_ERROR;
>
> BUG_ON(!valid_dma_direction(dir));
>
> /* Don't allow RAM to be mapped */
> BUG_ON(pfn_valid(PHYS_PFN(phys_addr)));
>
> - addr = phys_addr;
> - if (ops && ops->map_resource)
> + if (dma_is_direct(ops))
> + addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);
> + else if (ops->map_resource)
> addr = ops->map_resource(dev, phys_addr, size, dir, attrs);
Might it be reasonable to do:
if (!dma_is_direct(ops) && ops->map_resource)
addr = ops->map_resource(...);
else
addr = dma_direct_map_resource(...);
and avoid having to explicitly wire up the dma_direct callback elsewhere?
Robin.
>
> debug_dma_map_resource(dev, phys_addr, size, dir, addr);
> -
> return addr;
> }
>
> @@ -369,7 +371,7 @@ static inline void dma_unmap_resource(struct device *dev, dma_addr_t addr,
> const struct dma_map_ops *ops = get_dma_ops(dev);
>
> BUG_ON(!valid_dma_direction(dir));
> - if (ops && ops->unmap_resource)
> + if (!dma_is_direct(ops) && ops->unmap_resource)
> ops->unmap_resource(dev, addr, size, dir, attrs);
> debug_dma_unmap_resource(dev, addr, size, dir);
> }
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 355d16acee6d..8e0359b04957 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -356,6 +356,20 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
> }
> EXPORT_SYMBOL(dma_direct_map_sg);
>
> +dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
> + size_t size, enum dma_data_direction dir, unsigned long attrs)
> +{
> + dma_addr_t dma_addr = phys_to_dma(dev, paddr);
> +
> + if (unlikely(!dma_direct_possible(dev, dma_addr, size))) {
> + report_addr(dev, dma_addr, size);
> + return DMA_MAPPING_ERROR;
> + }
> +
> + return dma_addr;
> +}
> +EXPORT_SYMBOL(dma_direct_map_resource);
> +
> /*
> * Because 32-bit DMA masks are so common we expect every architecture to be
> * able to satisfy them - either by not supporting more physical memory, or by
>
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