On Monday 04 November 2013, Jason Gunthorpe wrote: > On Mon, Nov 04, 2013 at 02:43:00PM -0700, Stephen Warren wrote: > > For DMA, it does look like Arnd's code was requesting it too, but that > > should also be fine; as long as no transactions are actually issued > > against that DMA slave channel, then the HW state shouldn't matter? > > TBH, I'm not really familiar with how the DMA slave API works. > > As long as the API and HW guarantees that the channel cannot do any > DMAs no matter what the connected IP does, it is obviously fine.. Right, to initiate a DMA, you need to at least request a channel, configure it, and submit a descriptor. This does only the first step, so I'm pretty it's ok. > But not all DMA is like that, eg bus master DMA in PCI requires > drivers to call pci_enable_device only after they disable DMA in the > device, which is why I mentioned it.. Yes, a DMA bus master device is different here and needs to be handled as you exlain. > It would be nice to see a general API like this unambiguously make > clear the steps required: > > - Gain access to registers > - Gain control of the device > - Enable DMA, bind interrupts, etc > - Finalize device setup > - Make the device visible to the rest of the system > > I've seen lots of drivers where the above is just not done right. I agree this would be nice, but it's probably out of scope of what we're trying to do here, unless you have better ideas for how to structure it. Arnd -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
