On Wed, Jun 05, 2013 at 09:31:39PM +0100, Nick Dyer wrote: > Dmitry Torokhov wrote: > >> We have made a deliberate choice to implement this via sysfs rather than > >> debugfs since it needs to work on devices that don't have debugfs enabled. > > > > Then they will have to enable it. Re-implementing something because > > someone might not enable needed subsystem is not a good idea. Let's > > say somebody disabled I2C - will you write your own implementation because > > of that? Of course not, you just say that for given functionality it > > is a prerequisite. > > debugfs is a debug filesystem. This interface is useful for purposes which > are not debug. What other purposes does it serve? I'd expect you need it during new board bringup. > I have to be pragmatic: I don't see debugfs enabled on most > shipping Android devices, and however much I tell them to enable debugfs > doesn't seem to hold much weight. You do not need to have debugfs enabled on shipping kernels, just the ones you use for integration work. > > It's partly path dependence - it was implemented like this because regmap > wasn't in mainline at the point when I wrote it. Having a dependency on > regmap would now be a API break complicating support of customers using > older kernels than mainline. I would also have to update a bunch of > software and documentation and people to know about the two different APIs. > The existing implementation already appears in shipping devices, so it is > well tested. This was never a good argument for introducing an interface into the kernel. > > >> In addition, there are some quirks about the way in which we have to > >> read/write registers which means regmap isn't a good fit. > > > > Could you please elaborate more on this? > > - the mxt chip caches the I2C read pointer, so you can get a performance > optimisation by not sending the address on every read/write (I haven't > implemented this yet but plan to) > - the address pointer can wrap around when you read the T5 message > processor, which would confuse regmap > - we require I2C retries in some cases due to way the chip handles sleep states > - I can't see how to map the object protocol (used on mxt chips) into the > way regmap treats register ranges > > I can look into porting on top of regmap. But it seems a pity to pepper > regmap with atmel_mxt_ts quirks just to save on three small functions in > the driver. This is not about saving 3 functions but rather the fact that individual register access is desired by many parties and instead of each driver implementing it's own solution (via a char device, sysfs, debugfs, etc) we should try to standardize on common userspace interface. Thanks. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
