Mathias Nyman wrote:
Evolution of the patch can be found in this thread:
http://www.spinics.net/lists/linux-usb/msg128495.html
I think version 8 was the final one.
I couldn't find any answers to my questions in that thread. The key
change to the patch was made between v1 and v2:
+ /* Try setting the coherent_dma_mask to 64 bits, then try 32 bits */
+ ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
+ if (ret) {
+ ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
+ if (ret)
+ return ret;
+ }
I still do not understand what situation would cause a 64-bit mask to
fail, but a 32-bit mask to succeed. If the driver says that the device
can support 64-bit DMA, why would that ever fail? That means that the
device can DMA anywhere, so there are no restrictions.
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