On Tuesday 16 October 2012 at 12:00:13, Linus Walleij wrote: > On Tue, Oct 16, 2012 at 8:51 AM, Lars Poeschel <poesc...@lemonage.de> wrote: > > On Monday 15 October 2012 at 15:00:12, Linus Walleij wrote: > >> > + /* if io is set to output, just return the saved value */ > >> > + if (gpio->gpioa_out & (1 << offset)) > >> > + return gpio->gpioa_val & (1 << offset); > >> > >> That's not going to work if the hardware changes state > >> behind the back of the driver right? Oh well, maybe > >> it doesn't matter. > > > > I thought about that and then did this "cache" only in case the gpio is a > > output to save to usb ping-pong that is needed otherwise. I thought that > > nothing can change to state of the output but the driver itself. > > On a second note there is already a standard mechanism for caching > registers in the kernel, and that is regmap. Sadly it's a bit > undocumented but there are several examples and the code > lives in drivers/base/regmap and include/linux/regmap.h
I had a look at regmap. This is interesting. But there is no regmap_bus implementation for usb. Are you pointing me in this direction ? ;-) I don't think you want me as a kernel newbie write this code. And another thing: I don't think this can be implemented in such a general way as it is done already for i2c or mmio. As you see in the example of my (viperboard-)adapter, there is a bunch bytes sent, just to set the direction bit in a register. And it is not guaranteed, that this "address" and "value" are at the same position for other usb adapters. And this is getting even worse, if I think of reading values out of the viperboard... I would stay at the "cache" implementation I presented in the patch - this is too special. Lars -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
