On Thu, Mar 17, 2016 at 04:52:55PM +0100, Arnd Bergmann wrote: > On Monday 14 March 2016 18:51:08 Peter Chen wrote: > > On Wed, Mar 09, 2016 at 05:16:50PM -0600, Li Yang wrote: > > > On Tue, Mar 8, 2016 at 9:40 PM, Bjorn Andersson > > > <bjorn.andersson@xxxxxxxxxx> wrote: > > > > On Tue, Mar 8, 2016 at 11:52 AM, Li Yang <leoli@xxxxxxxxxxxxx> wrote: > > > >> On Wed, Mar 2, 2016 at 4:59 PM, Li Yang <leoli@xxxxxxxxxxxxx> wrote: > > > >>> On Mon, Feb 22, 2016 at 4:07 PM, Bjorn Andersson > > > >>> <bjorn.andersson@xxxxxxxxxx> wrote: > > > >>>> On Mon 22 Feb 02:03 PST 2016, Srinivas Kandagatla wrote: > > > > > > > > I had the chance to go through this with Arnd and the verdict is that > > > > devices not described in DT should not do DMA (or allocate buffers for > > > > doing DMA). > > > > > > > > So I believe the solution is to fall back on Peter's description; the > > > > chipidea driver is the core driver and the Qualcomm code should just > > > > be a platform layer. > > > > > > > > My suggestion is that we turn the chipidea core into a set of APIs > > > > that can called by the platform specific pieces. That way we will have > > > > the chipidea core be the device described in the DT. > > > > > > But like I said, this problem is not just existing for chipidea > > > driver. We already found that the dwc3 driver is also suffering from > > > the same issue. I don't know how many other drivers are impacted by > > > this change, but I suspect there will be some. A grep of > > > platform_device_add() in driver/ directory returns many possible > > > drivers to be impacted. As far as I know, the > > > drivers/net/ethernet/freescale/fman/mac.c is registering child > > > ethernet devices that definitely will do dma. If you want to do this > > > kind of rework to all these drivers, it will be a really big effort. > > > > > > > +1 > > > > Yes, I think this DMA things should be covered by driver core too. > > > > I don't think it's a very widespread problem, there are only very few > developers that intentionally use this method, and some use the > platform_device_register_full() call to create a device with a known > mask, which is generally ok for the limited case where the driver > is only ever going to run on a single platform, but not in the > more general case that of_dma_configure is designed to handle. Even only for qualcomm platforms, it may be possible have different DMA masks at ARM64 platforms, so we may can't use a fixed value at glue layer driver. So, using of_dma_configure is suitable choice for DT platforms for this case, right? > > I think we should fix the drivers to consistently use the device > that was created by the platform (DT or ACPI or board file) > to pass that into the DMA API, anything else will just cause > more subtle bugs. > Although I don't know what kinds of bugs it may have, it may be met before, otherwise, why most of platform drivers need to call dma_set_coherent_mask or dma_coerce_mask_and_coherent explicitly -- Best Regards, Peter Chen -- 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
