On Fri, Mar 7, 2014 at 10:02 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Friday 07 March 2014, Santosh Shilimkar wrote: >> >> + >> >> + ret = dma_set_mask(dev, dma_mask); >> >> + if (ret < 0) { >> >> + dev_err(dev, "failed to set DMA mask %pad\n", &dma_mask); >> >> + dev->dma_mask = NULL; >> >> + return; >> >> + } >> >> + >> >> + dev_dbg(dev, "dma_pfn_offset(%#08lx) dma_mask(%pad)\n", >> >> + dev->dma_pfn_offset, dev->dma_mask); >> >> + >> >> + ret = dma_set_coherent_mask(dev, dma_mask); >> > >> > I think these 2 calls belong in the drivers, not here. >> > >> I also had same initial thought but Arnd mentioned that its a >> shared responsibility between ARCH and drivers. Driver which >> could be common between arches not always have the correct >> mask information and it can change based on which arch it >> is running. >> >> With some discussion back and forth, we thought updating >> the dma_mask while the device getting created, would be >> better place since we can find the arch capability at >> this centralise code and update it. >> >> Ofcourse its bit debatable as the question you asked is >> bit obvious as well. I let Arnd give his view here. > > If we set the mask *here*, we probably don't want to call 'dma_set_mask', but > write to the mask directly, or we could call dma_coerce_mask_and_coherent(), > which is really for overriding the mask pointer and value at once in cases > where you absolutely know what it should be. > > We do need to decide what interface we want to use in platform device drivers, > and I'm hoping that Russell has some idea which one he prefers: > > a) Follow what we do for PCI devices: assume that we can do DMA_MASK(32) > on any device, and have drivers call dma_set_mask(DMA_MASK(64)) on devices > that would like to do more than that, or call e.g. dma_set_mask(DMA_MASK(28)) > for devices that can do less than 32 bit, as given in the argument. This > approach would be most consistent with the way PCI works, but it doesn't > really work well for the case where the mask is less than 32-bit and the > device driver doesn't know that. > > b) Never have to call dma_set_mask() for platform devices and assume that the > platform code sets it up correctly. This would probably be the simpler > solution, and I can't think of any downsides at the moment. I don't think we want this. In the case of setting up 64-bit masters, it is typically the device that knows if it can do 64-bit DMA either thru a capabilities register or compatible value. That device specific knowledge should really stay within the device's driver. Rob > > In either case we probably want to call something like dt_dma_configure() > from dma_set_mask() again to make sure that we stay within the limits > imposed by the bus structure. > > 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