Hi Jean, > > Wouldn't it be > > simpler to split up the vt1211_refresh_device function and just read > > the registers that we're interested in in the individual read > > callbacks as oposed to calling vt1211_refresh_device and read > > everything? > > Again, there are reasons why we wrote the drivers that way, mind you ;) I'm certain of that I just wasn't obvious to me, that's why I asked. Sorry for being such a pain in the but I just wanted to know how and why things are implemented they way they are :-) That was my last question, promised :-) Next you'll see an updated patch that hopefully passes the bar... ...juerg > First reason, some hardware monitoring chips stop updating when they > are queried for register values. The idea of the cache was to group all > bus accesses, and then guarantee a period of tranquility to the chip so > that it can update the register values with fresh data. > > Second reason, if reading from a sysfs file was triggering a physical > access to the chip unconditionally, it means every user of the system > could saturate the bus this chip is connected to. With the cache, we > guarantee this can't happen. > > Writing can only be done by root, which is why we are not worried about > unconditional reads and writes in "set" sysfs callbacks. > > Third reason, or rather benefit, is to avoid duplicate reads when a > register contains more than one "logical value". For example, if a > register contains the fan clock dividers for all three fans, it's more > efficient to read it once and cache it, than to read it three times. > > -- > Jean Delvare >
