On Friday 18 March 2016 09:54:14 Peter Chen wrote: > > > > 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? Yes. > > 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 Any driver that wants to do 64-bit addressing on DMA should call dma_set_mask()/dma_set_coherent_mask() on its device and check the return code. No driver should call dma_coerce_mask_and_coherent() on its own device, it's basically always a bug and we named the function to make that more obvious. The problem with dma_coerce_mask_and_coherent() is that it just overrides whatever the platform knows about the device when the driver thinks it knows better. The reason for having those calls in a lot of drivers is that traditionally, ARM platforms booting with DT did not set up any DMA mask and the drivers worked around it by manually setting up a mask that happened to work for them (almost all 32-bit ARM devices need a 32-bit mask without coherency or offset or iommu, so that's easy). We now call of_dma_configure() for all devices that get probed from DT, so we should be removing those calls. Arnd -- 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
