On Fri, Sep 2, 2016 at 5:43 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Thursday, September 1, 2016 5:14:28 PM CEST Leo Li wrote: >> >> Hi Felipe and Arnd, >> >> It has been a while since the last response to this discussion, but we >> haven't reached an agreement yet! Can we get to a conclusion on if it >> is valid to create child platform device for abstraction purpose? If >> yes, can this child device do DMA by itself? > > I'd say it's no problem for a driver to create child devices in order > to represent different aspects of a device, but you should not rely on > those devices working when used with the dma-mapping interfaces. > > This used to be simpler back when we could configure the kernel for > only one SoC platform at a time, and the platforms could provide their > own overrides for the dma-mapping interfaces. These days, we rely on > firmware or bootloader to describe various aspects of how DMA is done, > so you can't assume that passing a device without an of_node pointer > or ACPI data into those functions will do the right thing. Can we use the firmware or bootloader information to provide the default dma-mapping attributes for devices that doesn't have an of_node pointer or ACPI data? This will at least restore what we had previously provided . I'm concerned that changing all the drivers that are creating child device will be a big effort. Like I mentioned in another thread, there are many instances of platform_device_add() under the drivers/ directory. - Leo -- 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
