Hi! > >[Actually, you could _always_ do two reads on those devices, discard > >first result, and return the second. But I'm not sure how hardware > >will like that.] > > This would be the most sensible option. > > > However, let's analyze the typical use cases for flash strobing: > > > ------------------------------------------------------------- > > > >>>>>>>> Version without faults caching: > > ============ > Driver side: > ============ > > read_faults() > faults = read_i2c(); //read faults > if faults > write_i2c(); //clear faults, only for some devices > faults = read_i2c(); //read faults > return faults > > ================ > User space side: > ================ > > 1. faults = `cat flash_faults` //read_faults() > 2. if faults then > print "Unable to strobe the flash LED due to faults" > else > echo 1 > flash_strobe > > > >>>>>>>> Version with faults caching: > > ============ > Driver side: > ============ > > read_faults() > faults |= read_i2c(); //read faults > > clear_faults() > write_i2c(); //clear faults > faults = 0; > > > ================ > User space side: > ================ > > 1. faults = `cat flash_faults` //read_faults() > 2. if faults then > echo 0 > flash_faults //clear_faults() > faults = `cat flash_faults` //read_faults() > 3, if !faults > echo 1 > flash_strobe > else > print "Unable to strobe the flash LED due to faults" > > > ------------------------------------------------------------- > > From the above it seems that version with clearing faults on read > results in the simpler flash strobing procedure on userspace side, > by the cost of additional bus access on the driver side. I like caching version more (as it will allow by-hand debugging of "why did not flash fire? Aha, lets see in the file, there was fault), but both should be acceptable. > we don't need additional attribute, just writing the flash_faults > attribute can do the clearing. Yes, writing flash_faults to clear is acceptable. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
