Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems
On Tue, 11 May 2010, FUJITA Tomonori wrote:
Yes, you're right about that.
The DMA stuff is simple enough in this case. The urb->transfer_buffer address is passed to dma_map_single(), and the DMA address it returns is stored in urb->transfer_dma. Those are the two values printed out by the debugging patch.
Alan Stern
On Tue, 11 May 2010 10:00:50 -0400 (EDT) Alan Stern stern@rowland.harvard.edu wrote:
You've already confirmed that all the returned addresses (urb->transfer_dma) in the log is less than 4GB, right?
Drivers need to take care of more things (not only about addresses) to do DMA properly, that is, use the DMA API in the proper way (such as, once calling dma_map_single, drivers can't touch the buffer until calling dma_unmap_single)
Using the DMA API and performing DMA transfer in different places just make things complicated.
Is that address (urb->transfer_dma) the same as 'virt_to_phys(urb->transfer_buffer)' (if not, then SWIOTLB is being utilized) and is the dma_sync_* done on the urb->transfer_dma (to properly sync the data from the SWIOTLB to the transfer_buffer) before you start using the urb->transfer_buffer?
On Tue, 11 May 2010 10:24:40 -0400 Konrad Rzeszutek Wilk konrad.wilk@oracle.com wrote:
Or calling dma_unmap_single.
Can you tell me all the exact process of DMA that the usb core and the driver do?
On Tue, 11 May 2010, FUJITA Tomonori wrote:
1. The audio driver stores data in urb->transfer_buffer.
2. The audio driver calls usb_submit_urb(urb).
3. The USB core does urb->transfer_dma = dma_map_single(controller, urb->transfer_buffer, urb->transfer_buffer_length, DMA_TO_DEVICE);
4. The host controller driver tells the hardware to carry out the data transfer.
5. When the hardware says the transfer is finished, the USB core does dma_unmap_single(controller, urb->transfer_dma, urb->transfer_buffer_length, DMA_TO_DEVICE);
6. The audio driver's completion handler is called: (urb->complete)(urb);
Alan Stern
On Tue, 11 May 2010 11:04:55 -0400 (EDT) Alan Stern stern@rowland.harvard.edu wrote:
How urb->transfer_buffer is allocated?
The mapping error is checked via dma_mapping_error? Even if an mapping error happens, no data corruption happens due to that (needs something like retrying the request)?
The driver does only DMA_TO_DEVICE? Or you see DMA problems only with DMA_TO_DEVICE?
participants (3)
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Alan Stern
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FUJITA Tomonori
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Konrad Rzeszutek Wilk