Re: USB mass storage and ARM cache coherency

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Wed, 2010-02-17 at 10:15 +0100, Oliver Neukum wrote:
> We should have changed the subject line.
> 
> There's a second problem. It turns out that on ARM
> mapping for DMA must not be done if PIO will be used. Some HCDs
> use PIO for some transfers but DMA for others. The generic layer
> must learn about this. 

Ah, that makes a lot of sense and the same problem would happen on
any non-DMA coherent architecture, including some embedded ppc's.

I can see why the dma unmap would invalidate the dcache and blow
away the PIO.

What bugs me here is that the dma_map_* operation should always
be done at the lowest level, ie, the actual HCD driver, and thus
it should be up to the HCD to decide whether to dma_map or not
depending on whether it's going to do DMA or not. I haven't
scrutinized USB lately but if that isn't the case and the dma_map_*
operations are done behind your back by the USB core then that needs to
be changed in a way or another, or hooked at least.

Cheers,
Ben.


--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Linux Media]     [Linux Input]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Old Linux USB Devel Archive]

  Powered by Linux