Messages in this thread | | | Subject | Re: [PATCH v4 1/4] Produce system time from correlated clocksource | Date | Wed, 14 Oct 2015 18:57:33 -0700 | From | "Christopher Hall" <> |
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Thomas,
On Tue, 13 Oct 2015 12:42:52 -0700, Thomas Gleixner <tglx@linutronix.de> wrote: > On Mon, 12 Oct 2015, Christopher S. Hall wrote: >> audio. > > This wants to be a seperate patch, really.
OK. This makes sense, I'll do this the next time.
>> +/* This needs to be 3 or greater for backtracking to be useful */ > > Why?
The current index points to a copy and the next may be being changed by update_wall_time(). Leaving n-2 entries available with useful history in them. I'll add more descriptive comments here.
> >> +#define SHADOW_HISTORY_DEPTH 7 > > And that number is 7 because?
Due to power of 2 it will be 8 instead. As above the useful history is 8-2*1 ms (1 ms is the minimum jiffy length). Array size 4 would not be enough history for the DSP which requires 4 ms of history, in the worst case.
>> +static int shadow_index = -1; /* incremented to zero in > > What's the point of this? Aside of that, please do not use tail comments.
It's removed. A check for validity is added below and this isn't necessary.
> That's silly. Make DEPTH a power of 2 and do: > > idx = (idx + 1) & (DEPTH - 1);
This is changed.
>> + true : *shadow_index_out < shadow_index; > > All this can go away.
Yes.
>> + /* Also make sure that entry is valid based on current shadow_index */ >> + *shadow_index_io = ret; >> + return true; > > You surely try hard to do stuff in the most unreadable way.
Is like this easier to follow?
+static struct timekeeper *search_shadow_history(cycles_t cycles, + struct clocksource *cs) +{ + struct timekeeper *tk = &tk_core.timekeeper; + int srchidx = shadow_index; + cycles_t cycles_start, cycles_end; + + cycles_start = tk->tkr_mono.cycle_last; + do { + srchidx = !srchidx-- ? srchidx+SHADOW_HISTORY_DEPTH : srchidx; + tk = shadow_timekeeper + srchidx; + + /* The next shadow entry may be in flight, don't use it */ + if (srchidx == ((shadow_index+1) & (SHADOW_HISTORY_DEPTH-1))) + return NULL; + + /* Make sure timekeeper is related to clock on this interval */ + if (tk->tkr_mono.clock != cs) + return NULL; + + cycles_end = cycles_start; + cycles_start = tk->tkr_mono.cycle_last; + } while (!cycle_between(cycles_start, cycles, cycles_end)); + + return tk; +} A check for validity is added here using the clocksource pointer.
and inside of get_correlated_timestamp():
+ * into account. If the value is in the past, try to backtrack + */ + cycles_end = tk->tkr_mono.read(tk->tkr_mono.clock); + cycles_start = tk->tkr_mono.cycle_last; + if (!cycle_between(cycles_start, cycles, cycles_end)) { + tk = search_shadow_history(cycles, crs->related_cs); + if (!tk) + return -EAGAIN; + }
>> + /* >> + * Get a timestamp from the device if get_ts is non-NULL >> + */ >> + if( crt->get_ts ) { >> + ret = crt->get_ts(crt); >> + if (ret) >> + return ret; >> + } > > What's the point of this? Why are you not making the few lines which > you can actually reuse a helper function and leave the PTP code alone?
The audio driver is structured in such a way that it's simpler to provide a value rather than a callback. I changed this to allow the audio developers to provide an ART value as input. If a callback is provided, the resulting counter value is guaranteed to be later than cycle_last and there is no need to do extra checking (the goto skips that check). Is this an answer to your question?
> So I reached enf of patch and did not find anything in > timekeeping_init() which tells that the index is incremented to 0. It > really would need a comment, but why do you want to do that at all. It > does not matter whether the first entry is at 0 or 1. You need a > validity check for the entries anyway.
I think this should be resolved. There's no sensitivity with regard to the start index with an added validity check.
Thanks, Chris
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