Hello, On Tue, 10 Mar 2015 16:05:36 -0500, Felipe Balbi <balbi@xxxxxx> wrote: > I don't get it, why is it so that only mips needs this ? What's special > about mips' writel/readl implementation that it can't be used here ? > > This works for everybody else. Would it be a design oddity of this SoC that device registers do match CPU endianness, instead of matching implementations used in other SoCs ? This is the first time I ever get to debug some endianness issue in a driver, let alone on a SoC. I have extremely little knowledge of how this is expected to happen in general. Please pardon my naivety. AFAIK the Raspberry Pi is another SoC where this device is present, and the RPi is little endian. As this driver works there, it suggests the registers are little-endian too. I think proposed change will not break this, as discussed with John Youn on previous submission. I couldn't get a reasonable RPi kernel build environment (because of the lack of working kernel .config for a recent kernel) to verify this though. > Is it so that dwc2 and cpu endianness don't match here ? They do match actually. It's readl/writel internal byte swapping happening on big-endian archs which breaks this. Once straightened as per Antti's patch, the driver detects the HCD and USB devices work fine. Well, actually there is one out-of-driver (platform-specific) register to set so DMA transfers match CPU endianness (I have no idea why it doesn't default to the working setting). > weren't readl() and writel() already supposed to handle endianness for > us? If asm-generic implementation is representative of the intent, then the intent is clearly to read little-endian values from memory and convert to CPU endianness. http://lxr.free-electrons.com/source/include/asm-generic/io.h#L127 http://lxr.free-electrons.com/source/include/asm-generic/io.h#L161 Which brings me back to my original questions: Is SoC hardware expected to expose registers in cpu-consistent endianness (or maybe even "default-cpu-endianness") ? > wrong comment style. Expected style is to prefix lines with * and to end block below these, right ? Nice catch, thanks. Regards, -- Vincent Pelletier -- 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
