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SubjectRe: [RFC PATCH 1/4] dma-mapping: Generalise dma_32bit_limit flag
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On 10/07/18 19:04, Christoph Hellwig wrote:
> On Tue, Jul 10, 2018 at 06:17:16PM +0100, Robin Murphy wrote:
>> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
>> index 8be8106270c2..95e185347e34 100644
>> --- a/kernel/dma/direct.c
>> +++ b/kernel/dma/direct.c
>> @@ -183,7 +183,7 @@ int dma_direct_supported(struct device *dev, u64 mask)
>> * Various PCI/PCIe bridges have broken support for > 32bit DMA even
>> * if the device itself might support it.
>> */
>> - if (dev->dma_32bit_limit && mask > DMA_BIT_MASK(32))
>> + if (dev->bus_dma_mask && mask > dev->bus_dma_mask)
>> return 0;
>
> The comment above this check needs an updated (or just be removed).

Right, I'll give it a tweak. I could also do with actually getting the
field name correct in via_no_dac_cb()...

> Also we still have a few architectures not using dma-direct. I guess
> most were doing fine without such limits anyway, but at least arm
> will probably need an equivalent check.

Indeed, once we've found an approach that everyone's happy with we can
have a more thorough audit of exactly where else it needs to be applied.
FWIW I'm not aware of any 32-bit Arm systems affected by this*, but if
they do exist then at least there's no risk of regression since they've
always been busted.

Robin.


* Not counting the somewhat-similar StrongArm DMA controller bug where
one bit in the *middle* of the mask is unusable. Let's keep that
confined to the Arm dmabounce code and never speak of it...
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