On Mon, Feb 21, 2022 at 05:30:45PM +0000, Jonathan Cameron wrote: > On Mon, 21 Feb 2022 19:04:38 +0200 > Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> wrote: > > > On Mon, Feb 21, 2022 at 01:48:12PM +0100, Nuno Sá wrote: > > > On Sun, 2022-02-20 at 13:32 +0200, Andy Shevchenko wrote: > > > > On Fri, Feb 18, 2022 at 02:51:28PM +0100, Nuno Sá wrote: > > > > > On Mon, 2022-02-14 at 15:49 +0200, Andy Shevchenko wrote: > > > > > > On Mon, Feb 07, 2022 at 09:19:46PM +0100, Nuno Sá wrote: > > > > > > > On Mon, 2022-02-07 at 13:09 +0200, Andy Shevchenko wrote: > > > > > > > > On Sun, Feb 06, 2022 at 01:19:59PM +0000, Sa, Nuno wrote: > > > > > > > > > > From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> > > > > > > > > > > Sent: Saturday, February 5, 2022 6:30 PM > > > > > > > > > > On Fri, Jan 21, 2022 at 03:24:59PM +0100, Nuno Sá wrote: > > > > ... > > > > > > > > > > > > > + ret = kstrtou16(buf, 10, &val); > > > > > > > > > > > > > > > > > > > > In other function you have long, here u16. I would expect that > > > > > > > > > > the types are of the same class, e.g. if here you have u16, > > > > > > > > > > then there something like s32 / s64. Or here something like > > > > > > > > > > unsigned short. > > > > > > > > > > > > > > > > > > > > A bit of elaboration why u16 is chosen here? > > > > > > > > > > > > > > > > > > Well, I never really saw any enforcement here to be honest > > > > > > > > > (rather than using stdint types...). So I pretty much just use > > > > > > > > > these in unsigned types because I'm lazy and u16 is faster to > > > > > > > > > type than unsigned short... In this case, unless Jonathan really > > > > > > > > > asks for it, I prefer not to go all over the driver and change > > > > > > > > > this... > > > > > > > > > > > > > > > > This is about consistency. It may work as is, but it feels not good > > > > > > > > when for int (or unsigned int) one uses fixed-width types. Also > > > > > > > > it's non- written advice to use fixed-width variables when it's > > > > > > > > about programming registers or so, for the rest, use POD types. > > > > > > > > > > Ok, going a bit back in the discussion, you argued that in one place I > > > > > was using long while here u16. Well, in the place I'm using long, that > > > > > was on purpose because that value is to be compared against an array of > > > > > longs (which has to be long because it depends on CCF rates). I guess I > > > > > can als0 use s64, but there is also a reason why long was used. > > > > > > > > > > In the u16 case, we really want to have 2 bytes because I'm going to use > > > > > that value to write the dac code which is 2 bytes. > > > > > > > > Okay, that's what I want to hear. If it's indeed goes to be a value to the > > > > register, then it's fine. > > > > > > > > Perhaps a comment? > > > > > > I guess you mean to have a comment to state that here we have fixed > > > size type (as opposed to long, used in another place), because we > > > directly use the value on a register write? > > > > > > Asking it because I'm not planning to add comments in all the places > > > where I have fixed size types for register read/writes... > > > > Thinking more about it and now I'm convinced that using the value that goes to > > the register in ABI is bad idea (means that user space must not care about the > > size or contents of the hardware register and should be abstract representation > > of the HW). > > > > OTOH this seems to be "raw" value of something. So, I maybe missed the convention > > in IIO about this kind of values WRT the variable types used on ABI side. > > > > That said, I leave it to Jonathan since I'm not convinced that u16 is a proper > > choice here. > > From a userspace point of view it doesn't care as it's writing a string. > In this particular case the string only has valid values that from 0-(2^16-1) > (i.e. 16 bits). So if it writes outside of that range it is an error. > You could read it into an unsigned long and then check against the range, > but there is little point given you'd still return an error if it was out of > range. The fact that kstrto16() does that for you really just a shortcut > though it will return -ERANGE rather than perhaps -EINVAL which might be used > for a more generic "not this value". > > Userspace can also read the range that is acceptable from > out_voltage0_raw_available [0 1 2^16-1] and hence not write an invalid value > in the first place - which is obviously preferred to getting an error. > Scaling etc is also expressed to userspace so it it wants to write a particular > voltage it can perform the appropriate scaling. Note that moving linear scaling > like this to userspace allows easy use of floating point + may be a significant > performance advantage if using the chrdev interface which uses the same > approach (and values) as the sysfs interface. With the same logic it can be unsigned short, no? The point is to use u16 when it's indeed fixed-width value that goes to hardware or being used as part of a protocol. And thus mentioning of the IOCTL protocols may justify the choice. Then the question to the other values, shouldn't they be also fixed-width ones? > > > > > > > I can understand your reasoning but again this is something that I > > > > > > > never really saw being enforced. So, I'm more than ok to change it if > > > > > > > it really becomes something that we will try to "enforce" in IIO. > > > > > > > Otherwise it just feels as a random nitpick :). > > > > > > > > > > > > No, this is about consistency and common sense. If you define type uXX, > > > > > > we have an API for that exact type. It's confusing why POD type APIs > > > > > > are used with fixed-width types or vise versa. > > > > > > > > > > > > Moreover (which is pure theoretical, though) some architectures might > > > > > > have no (mutual) equivalency between these types. -- With Best Regards, Andy Shevchenko
