On Mon, Feb 26, 2018 at 5:59 PM, Oliver Neukum <oneukum@xxxxxxxx> wrote: > Am Donnerstag, den 15.02.2018, 11:00 +0200 schrieb Ran Shalit: >> I actually asked about DMA, because I see that it is possible to send >> urb using DMA allocated buffers or not (coherent and non-coherent) >> usb_buffer_alloc(). >> So, How can we actually know if I should use this API with a device or >> not ? I mean, is it always possible to use the coherent buffer with >> the device ? > > Hi, > > it is always possible to use usb_alloc_coherent() on a host. > But it is generally not sensible. It is for buffers to be reused > many times. In general use kmalloc() [once per buffer. That is a rule. > You must not share them.] > > HTH > Oliver > Hi Oliver, Is the dma engine which is responsible for the transaction is actually in the usb device (It's not dma controller in host) ? If I understand correctly in both ways (kmalloc or usb_alloc_coherent), then we are allocating buffers might be used for dma. Even if DMA is not used in the transaction, than is shall still be functional with the same DMA-allocated buffers. Thanks, ranran -- 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
