UPSTREAM: coresight: tmc-etr: Fix updating buffer in not-snapshot mode.

(Upstream commit 13af88f312fc57becacfcbb1cc77f844281a30ec).

TMC etr always copies all available data to perf aux buffer, which
may exceed the available space in perf aux buffer. It isn't suitable
for not-snapshot mode, because:
1) It may overwrite previously written data.
2) It may make the perf_event_mmap_page->aux_head report having more
or less data than the reality.

So change to only copy the latest data fitting the available space in
perf aux buffer.

Signed-off-by: Yabin Cui <yabinc@google.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20190829202842.580-14-mathieu.poirier@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Bug: 140266694
Change-Id: Idcdd505c77637d0dc3329a1d145ddca20ca895da
Signed-off-by: Yabin Cui <yabinc@google.com>