On Wed, Jul 23, 2003 at 02:30:53AM +0200, Maciej W. Rozycki wrote: > On Tue, 22 Jul 2003, Jun Sun wrote: > > > Isn't it cool to take care of the board-specific with the same interface > > kernel time system uses? Every MIPS board gets a basic RTC driver for free! > > Well, I'm not that convinced. What's wrong with making real support for > the RTC chip instead? > Nothing wrong with full RTC driver support - it is just that when 30+ MIPS boards don't have to add #ifdef's to rtc.c and mc146818rtc.h and hwclock still works people start appreciate more about the existence of rtc_set_time(). > > > > What is the race condition? And what is the performance hit? > > You need to read from the RTC, modify minutes and seconds as appropriate > and write the RTC back. Meanwhile the time as stored in the RTC may > change. With the 500 ms offset approximation as used by time.c it may be > unlikely, but that assumption is for the MC146818 and it may not be true > for incompatible RTC chips. That is the race. The performance hit is > obvious -- now a read is added to the write. > OK, I see the performance hit now. If you really want, how about the following change: 1) add set_rtc_mmss() function pointer in asm/time.h. 2) set it equal to set_rtc_time in time_init(). Board can override this decision in board_timer_setup() for better performance. 3) RTC update is changed to call set_rtc_mmss() How does this sound? It leaves all existing code unchanged, while gives a way for optimization. The default setting of set_rtc_mmss to set_rtc_time makes logical sense too, because set_rtc_mmss is really a "back door" version of set_rtc_time(). Jun
