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SubjectRe: [PATCH 4/5] dma-direct: implement complete bus_dma_mask handling
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On 20/09/18 19:52, Christoph Hellwig wrote:
> Instead of rejecting devices with a too small bus_dma_mask we can handle
> by taking the bus dma_mask into account for allocations and bounce
> buffering decisions.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> include/linux/dma-direct.h | 3 ++-
> kernel/dma/direct.c | 21 +++++++++++----------
> 2 files changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
> index b79496d8c75b..fbca184ff5a0 100644
> --- a/include/linux/dma-direct.h
> +++ b/include/linux/dma-direct.h
> @@ -27,7 +27,8 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size)
> if (!dev->dma_mask)
> return false;
>
> - return addr + size - 1 <= *dev->dma_mask;
> + return addr + size - 1 <=
> + min_not_zero(*dev->dma_mask, dev->bus_dma_mask);
> }
> #endif /* !CONFIG_ARCH_HAS_PHYS_TO_DMA */
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 3c404e33d946..64466b7ef67b 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -43,10 +43,11 @@ check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
> return false;
> }
>
> - if (*dev->dma_mask >= DMA_BIT_MASK(32)) {
> + if (*dev->dma_mask >= DMA_BIT_MASK(32) || dev->bus_dma_mask) {

Hmm... say *dev->dma_mask is 31 bits and dev->bus_dma_mask is 40 bits
due to a global DT property, we'll now scream where we didn't before
even though the bus mask is almost certainly irrelevant - is that desirable?

> dev_err(dev,
> - "%s: overflow %pad+%zu of device mask %llx\n",
> - caller, &dma_addr, size, *dev->dma_mask);
> + "%s: overflow %pad+%zu of device mask %llx bus mask %llx\n",
> + caller, &dma_addr, size,
> + *dev->dma_mask, dev->bus_dma_mask);
> }
> return false;
> }
> @@ -65,12 +66,18 @@ u64 dma_direct_get_required_mask(struct device *dev)
> {
> u64 max_dma = phys_to_dma_direct(dev, (max_pfn - 1) << PAGE_SHIFT);
>
> + if (dev->bus_dma_mask && dev->bus_dma_mask < max_dma)
> + max_dma = dev->bus_dma_mask;

Again, I think we could just do another min_not_zero() here. A device
wired to address only one single page of RAM isn't a realistic prospect
(and we could just flip the -1 and the shift in the max_dma calculation
if we *really* wanted to support such things).

> +
> return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
> }
>
> static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
> u64 *phys_mask)
> {
> + if (dev->bus_dma_mask && dev->bus_dma_mask < dma_mask)
> + dma_mask = dev->bus_dma_mask;
> +

Similarly, can't we assume dma_mask to be nonzero here too? It feels
like we really shouldn't have managed to get this far without one.

Robin.

> if (force_dma_unencrypted())
> *phys_mask = __dma_to_phys(dev, dma_mask);
> else
> @@ -87,7 +94,7 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
> static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
> {
> return phys_to_dma_direct(dev, phys) + size - 1 <=
> - dev->coherent_dma_mask;
> + min_not_zero(dev->coherent_dma_mask, dev->bus_dma_mask);
> }
>
> void *dma_direct_alloc_pages(struct device *dev, size_t size,
> @@ -291,12 +298,6 @@ int dma_direct_supported(struct device *dev, u64 mask)
> if (mask < phys_to_dma(dev, DMA_BIT_MASK(32)))
> return 0;
> #endif
> - /*
> - * Upstream PCI/PCIe bridges or SoC interconnects may not carry
> - * as many DMA address bits as the device itself supports.
> - */
> - if (dev->bus_dma_mask && mask > dev->bus_dma_mask)
> - return 0;
> return 1;
> }
>
>

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