On 9/7/20 9:57 AM, Simon Glass wrote: > Hi Sean, > > On Sun, 6 Sep 2020 at 20:02, Sean Anderson <sean...@gmail.com> wrote: >> >> On 9/6/20 9:43 PM, Simon Glass wrote: >>> Hi Sean, >>> >>> On Tue, 1 Sep 2020 at 13:56, Sean Anderson <sean...@gmail.com> wrote: >>>> >>>> get_ticks does not always succeed. Sometimes it can be called before the >>>> timer has been initialized. If it does, it returns a negative errno. >>>> This causes the timer to appear non-monotonic, because the value will >>>> become much smaller after the timer is initialized. >>>> >>>> No users of get_ticks which I checked handle errors of this kind. Further, >>>> functions like tick_to_time mangle the result of get_ticks, making it very >>>> unlikely that one could check for an error without suggesting a patch such >>>> as this one. >>>> >>>> This patch changes get_ticks to always return 0 when there is an error. >>>> 0 is the least unsigned integer, ensuring get_ticks appears monotonic. This >>>> has the side effect of time apparently not passing until the timer is >>>> initialized. However, without this patch, time does not pass anyway, >>>> because the error value is likely to be the same. >>>> >>>> Fixes: c8a7ba9e6a5 >>>> Signed-off-by: Sean Anderson <sean...@gmail.com> >>>> --- >>>> >>>> lib/time.c | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> Would it be better to panic so people can fix the bug? >> >> I thought this was expected behavior. It's only a bug if you do >> something like udelay before any timers are created. We just can't >> report errors through get_ticks, because its users assume that it always >> returns a time of some kind. > > I think it indicates a bug. If you use a device before it is ready you > don't really know what it will do. I worry that this patch is just > going to cause confusion, since the behaviour depends on when you call > it. If we panic, people can figure out why the timer is being inited > too late, or being used too early.
Hm, maybe. I don't think it's as clear cut as "us[ing] a device before it is ready," because get_ticks tries to initialize the timer if it isn't already initialized. Unless someone else does it first, the first call to get_ticks will always be before the timer is initialized. The specific problem I ran into was that after relocation, the watchdog may be initialized before the timer. This occurs on RISC-V because without [1] a timer only exists after arch_early_init_r. So, for the first few calls to watchdog_reset there is no timer. The second return could probably be turned into a panic. I checked, and all current timer drivers always succeed in getting the time (except for the RISC-V timer, which is fixed in [1]), so the only way for timer_get_count to fail is if timer_ops.get_count doesn't exist. That is almost certainly an error on the driver author's part, so I think panicking there is the only reasonable option. (Does get_count even need to have a return value? I think it's reasonable to always expect the timer to return a value.) --Sean [1] https://patchwork.ozlabs.org/project/uboot/list/?series=198797