Quoting Alexandre Belloni (2019-10-05 13:05:21)

On 24/09/2019 13:20:15-0700, Stephen Boyd wrote:

quoted

Quoting Uwe  (2019-09-24 05:21:47)

quoted

On Fri, Sep 20, 2019 at 05:39:06PM +0200, Alexandre Belloni wrote:

quoted

Note that this was already discussed a while ago and Arnd said this approach was
reasonable:
  https://lore.kernel.org/lkml/6120818.MyeJZ74hYa@wuerfel/ (local)

 drivers/clk/at91/clk-main.c |  5 ++++-
 drivers/clk/at91/sckc.c     | 20 ++++++++++++++++----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/clk/at91/clk-main.c b/drivers/clk/at91/clk-main.c
index f607ee702c83..ccd48e7a3d74 100644
--- a/drivers/clk/at91/clk-main.c
+++ b/drivers/clk/at91/clk-main.c

@@ -293,7 +293,10 @@ static int clk_main_probe_frequency(struct regmap *regmap)
              regmap_read(regmap, AT91_CKGR_MCFR, &mcfr);
              if (mcfr & AT91_PMC_MAINRDY)
                      return 0;
-             usleep_range(MAINF_LOOP_MIN_WAIT, MAINF_LOOP_MAX_WAIT);
+             if (system_state < SYSTEM_RUNNING)
+                     udelay(MAINF_LOOP_MIN_WAIT);
+             else
+                     usleep_range(MAINF_LOOP_MIN_WAIT, MAINF_LOOP_MAX_WAIT);

Given that this construct is introduced several times, I wonder if we
want something like:

        static inline void early_usleep_range(unsigned long min, unsigned long max)
        {
                if (system_state < SYSTEM_RUNNING)
                        udelay(min);
                else
                        usleep_range(min, max);
        }

Maybe, but I think the intent is to not encourage this behavior? So
providing a wrapper will make it "easy" and then we'll have to tell
users to stop calling it. Another idea would be to make usleep_range()
"do the right thing" and call udelay if the system isn't running. And
another idea from tlgx[1] is to pull the delay logic into another clk op
that we can call to see when the enable or prepare is done. That may be
possible by introducing another clk_ops callback that when present
indicates we should sleep or delay for so much time while waiting for
the prepare or enable to complete.

[1] https://lkml.kernel.org/r/alpine.DEB.2.11.1606061448010.28031@nanos

Do you want me to implement that now or are you planning to apply the
patch in the meantime ?

 
I'll just apply this for now to clk-fixes and merge it up next week. It
would be great to do the other idea though, as a long term effort to
reduce all the busy loop code we have in clk drivers. No worries, I'll
put it on the todo list.


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