[v2,0/3] i2c: i2c-qcom-geni: More properly fix the DMA race

Message

Doug Anderson Oct. 13, 2020, 9:25 p.m. UTC

Previously I landed commit 02b9aec59243 ("i2c: i2c-qcom-geni: Fix DMA
transfer race") to fix a race we were seeing.  While that most
definitely fixed the race we were seeing, it looks like it causes
problems in the TX path, which we didn't stress test until we started
trying to update firmware on devices.

Let's revert that patch and try another way: fix the original problem
by disabling the interrupts that aren't relevant to DMA transfers.
Now we can stress both TX and RX cases and see no problems.  I also
can't find any place to put an msleep() that causes problems anymore.

Since this problem only affects i2c, I'm hoping for an Ack from Bjorn
and then all these patches can go through the i2c tree.  However, if
maintainers want to work a different way out to land that's OK too.

NOTE: the 3rd patch in the series could certianly be squashed with
patch #1 or I could re-order / rejigger.  To me it seemed like a good
idea to first fix the probelm (and make the two functions as much of
an inverse as possible) and later try to clean things up.  Yell if you
want something different.

Changes in v2:
- Consistently use "val_old" to keep track of old value.
- Add comments about why UART is special.

Douglas Anderson (3):
  soc: qcom: geni: More properly switch to DMA mode
  Revert "i2c: i2c-qcom-geni: Fix DMA transfer race"
  soc: qcom: geni: Optimize/comment select fifo/dma mode

 drivers/i2c/busses/i2c-qcom-geni.c |  6 ++--
 drivers/soc/qcom/qcom-geni-se.c    | 55 ++++++++++++++++++++++--------
 2 files changed, 43 insertions(+), 18 deletions(-)