On 9/8/20 7:56 PM, Simon Glass wrote: > Hi Sean, > > On Mon, 7 Sep 2020 at 09:51, Sean Anderson <sean...@gmail.com> wrote: >> >> 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. > > OK good, let's do that and update docs in timer.h
That being to panic both times, or just panic the second time? --Sean