> -----Original Message----- > From: Oliver Neukum [mailto:oliver@xxxxxxxxxx] > Sent: Tuesday, February 16, 2010 7:03 PM > To: Russell King - ARM Linux > Cc: Shilimkar, Santosh; Catalin Marinas; Pavel Machek; Greg KH; Matthew Dharm; Sergei Shtylyov; Ming > Lei; Sebastian Siewior; linux-usb@xxxxxxxxxxxxxxx; linux-kernel; linux-arm-kernel; Mankad, Maulik > Ojas > Subject: Re: USB mass storage and ARM cache coherency > > Am Dienstag, 16. Februar 2010 10:39:46 schrieb Russell King - ARM Linux: > > However, because ARM CPUs can now speculatively prefetch, just leaving it > > at that results in corruption of buffers used for DMA. So we have to > > invalidate DMA_FROM_DEVICE and DMA_BIDIRECTIONAL buffers on unmap to > > ensure coherency with DMA operations. > > > > If the CPU writes to a DMA_FROM_DEVICE buffer between map and unmap, the > > writes can sit in the cache, and on unmap, they will be discarded. > > > > Cleaning the cache on unmap is not an option; that too can lead to DMA > > buffer corruption in the DMA case. > > I am afraid for these controllers the controller driver must be responsible > for all DMA and cache issues. Indicating the exact requirements to the > upper layer would be a battle already lost. > so the safe choice is not to set has_dma and the generic layer will leave > the issue to the lower level. This means don't use dma at all which will almost kill the performance. Regards, Santosh -- 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
