Re: [PATCH v3 3/4] thermal/core: Build ascending ordered indexes for the trip points

[Daniel Lezcano]

On 19/07/2022 16:17, Zhang Rui wrote:
> On Tue, 2022-07-19 at 09:22 +0200, Daniel Lezcano wrote:
> > On 19/07/2022 03:14, Zhang Rui wrote:
> > > On Mon, 2022-07-18 at 15:21 +0200, Daniel Lezcano wrote:
> > > > Hi Zhang,
> > > >
> > > > thanks for the review
> > > >
> > > > On 18/07/2022 07:28, Zhang Rui wrote:
> > > > > On Fri, 2022-07-15 at 23:09 +0200, Daniel Lezcano wrote:
> > > >
> > > > [ ... ]
> > > >
> > > > > > Instead of taking the risk of breaking the existing
> > > > > > platforms,
> > > > > > use an
> > > > > > array of temperature ordered trip identifiers and make it
> > > > > > available
> > > > > > for the code needing to browse the trip points in an ordered
> > > > > > way.
> > > > > >
> > > > > > Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> > > > > > ---
> > > >
> > > > [ ... ]
> > > >
> > > > > > +static void sort_trips_indexes(struct thermal_zone_device
> > > > > > *tz)
> > > > > > +{
> > > > > > +       int i, j;
> > > > > > +
> > > > > > +       for (i = 0; i < tz->trips; i++)
> > > > > > +               tz->trips_indexes[i] = i;
> > > > > > +
> > > > > > +       for (i = 0; i < tz->trips; i++) {
> > > > > > +               for (j = i + 1; j < tz->trips; j++) {
> > > > > > +                       int t1, t2;
> > > > > > +
> > > > > > +                       tz->ops->get_trip_temp(tz, tz-
> > > > > > > trips_indexes[i], &t1);
> > > > >
> > > > > This line can be moved to the upper loop.
> > > >
> > > > Right, thanks!
> > > >
> > > > > > +                       tz->ops->get_trip_temp(tz, tz-
> > > > > > > trips_indexes[j], &t2);
> > > > > > +
> > > > >
> > > > > what about the disabled trip points?
> > > > >
> > > > > we should ignore those trip points and check the return value
> > > > > to
> > > > > make
> > > > > sure we're comparing the valid trip_temp values.
> > > >
> > > > We don't have to care about, whatever the position, the
> > > > corresponding
> > > > trip id will be disabled by the trip init function before calling
> > > > this
> > > > one and ignored in the handle_thermal_trip() function
> > >
> > > hah, I missed this one and replied to your latest reply directly.
> > >
> > > The thing I'm concerning is that if we don't check the return
> > > value,
> > > for a disabled trip point, the trip_temp (t1/t2) returned is some
> > > random value, it all depends on the previous value set by last
> > > successful .get_trip_temp(), and this may screw up the sorting.
> >
> > The indexes array is the same size as the trip array, that makes the
> > code much less prone to errors.
> >
> > To have the same number of trip points, the index of the disabled
> > trip
> > must be inserted also in the array. We don't care about its position
> > in
> > the indexes array because it is discarded in the handle_trip_point()
> > function anyway. For this reason, the random temperature of the
> > disabled
> > trip point and the resulting position in the sorting is harmless.
> >
> > It is made on purpose to ignore the return value, so we have a
> > simpler code.
> Let's take below case for example,
> say, we have three trip points 0, 1, 2, and trip point 1 is broken and
> disabled.
>
> trip temp for trip point 0 is 10 and for trip point 2 is 20.
> .get_trip_temp(tz, 1, &t) fails, and t is an uninitialized random value
>
>
> Initial:
>     trip_indexes[0]=0,trip_indexes[1]=1,trip_indexes[2]=2
> step1:
>     i=0,j=1
>     get trip temp for trip point trip_indexes[0]=0 and trip_indexes[1]=1
>     trip point 1 returns trip temp 5, and it swaps with trip point 0
>     so
>     trip_indexes[0]=1,trip_indexes[1]=0,trip_indexes[2]=2
> step2:
>     i=0,j=2
>     get trip temp for trip point trip_indexes[0]=1 and trip_indexes[2]=2
>     trip point 1 returns trip temp 25, and it swaps with trip point 2
>     so
>     trip_indexes[0]=2,trip_indexes[1]=0,trip_indexes[2]=1
>
> And the sorting is broken now.
>
> please correct me if I'm missing anything.

Oh, nice! Thanks for the detailed explanation.

We can initialize t1 and t2 to INT_MAX, so if the get_trip_temp() fails, 
they will be set to the maximum temperature and it will be at the end of 
the array.

Alternatively, we check the disabled bit and set the temperature to INT_MAX.





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