Re: [PATCH 1/4] Provide simple noop dma ops
Am 28.10.2015 um 01:41 schrieb Joerg Roedel:
> Hi Christian,
>
> On Tue, Oct 27, 2015 at 11:48:48PM +0100, Christian Borntraeger wrote:
>> +static dma_addr_t dma_noop_map_page(struct device *dev, struct page *page,
>> + unsigned long offset, size_t size,
>> + enum dma_data_direction dir,
>> + struct dma_attrs *attrs)
>> +{
>> +return page_to_phys(page) + offset;
>> +}
>
> X86 also has its own version of these noop dma_ops, see
> arch/x86/kernel/pci-nommu.c. This one also checks the dma_mask and
> prints a warning if the physical address doesn't fit into the mask.
>
> I think this would make sense here too, and that we can also make x86
> use the same generic noop-dma-ops your are introducing.
It not trivial without understanding the dma mask details. Do I read the x86
implementation right, that it limits the dma to 32 bit? Then we cannot collapse
both implementations. Or maybe we can hide this in dma_capable. Dont know
So I would prefer to keep it as is and let someone with x86 test environment do
the unification. Christoph, I think you wanted to do that anyway, are you
willing
to do that?
Christian
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/4] Provide simple noop dma ops
On Fri, Oct 30, 2015 at 01:55:56PM +0100, Christian Borntraeger wrote: > It not trivial without understanding the dma mask details. Do I read > the x86 implementation right, that it limits the dma to 32 bit? Then > we cannot collapse both implementations. Or maybe we can hide this in > dma_capable. Dont know No, DMA is not limited to 32bit on x86. Each device has its own dma_mask, and the requested address+size is checked against it. The DMA_BIT_MASK(32) check is only to there to print a warning when a 32bit capable device trys to access memory above 4GB. Joerg -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/4] Provide simple noop dma ops
Hi Christian,
On Tue, Oct 27, 2015 at 11:48:48PM +0100, Christian Borntraeger wrote:
> +static dma_addr_t dma_noop_map_page(struct device *dev, struct page *page,
> + unsigned long offset, size_t size,
> + enum dma_data_direction dir,
> + struct dma_attrs *attrs)
> +{
> + return page_to_phys(page) + offset;
> +}
X86 also has its own version of these noop dma_ops, see
arch/x86/kernel/pci-nommu.c. This one also checks the dma_mask and
prints a warning if the physical address doesn't fit into the mask.
I think this would make sense here too, and that we can also make x86
use the same generic noop-dma-ops your are introducing.
Joerg
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
