Hi Andrey,
On Mon, Mar 11, 2019 at 11:26:20AM -0700, Andrey Smirnov wrote:
> On Mon, Mar 4, 2019 at 4:30 AM Laurent Pinchart wrote:
> > On Tue, Feb 26, 2019 at 11:36:05AM -0800, Andrey Smirnov wrote:
> >> Replace explicit polling in tc_link_training() with equivalent call to
> >> regmap_read_poll_timeout() for simplicity. No functional change
> >> intended (not including slightly altered debug output).
> >>
> >> Signed-off-by: Andrey Smirnov <andrew.smir...@gmail.com>
> >> Cc: Archit Taneja <arch...@codeaurora.org>
> >> Cc: Andrzej Hajda <a.ha...@samsung.com>
> >> Cc: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
> >> Cc: Chris Healy <cphe...@gmail.com>
> >> Cc: Lucas Stach <l.st...@pengutronix.de>
> >> Cc: dri-devel@lists.freedesktop.org
> >> Cc: linux-ker...@vger.kernel.org
> >> ---
> >> drivers/gpu/drm/bridge/tc358767.c | 14 +++++---------
> >> 1 file changed, 5 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/bridge/tc358767.c
> >> b/drivers/gpu/drm/bridge/tc358767.c
> >> index 6455e6484722..ea30cec4a0c3 100644
> >> --- a/drivers/gpu/drm/bridge/tc358767.c
> >> +++ b/drivers/gpu/drm/bridge/tc358767.c
> >> @@ -735,7 +735,6 @@ static int tc_link_training(struct tc_data *tc, int
> >> pattern)
> >> const char * const *errors;
> >> u32 srcctrl = tc_srcctrl(tc) | DP0_SRCCTRL_SCRMBLDIS |
> >> DP0_SRCCTRL_AUTOCORRECT;
> >> - int timeout;
> >> int retry;
> >> u32 value;
> >> int ret;
> >> @@ -765,20 +764,17 @@ static int tc_link_training(struct tc_data *tc, int
> >> pattern)
> >> tc_write(DP0CTL, DP_EN);
> >>
> >> /* wait */
> >> - timeout = 1000;
> >> - do {
> >> - tc_read(DP0_LTSTAT, &value);
> >> - udelay(1);
> >> - } while ((!(value & LT_LOOPDONE)) && (--timeout));
> >> - if (timeout == 0) {
> >> + ret = regmap_read_poll_timeout(tc->regmap, DP0_LTSTAT, value,
> >> + value & LT_LOOPDONE, 1, 1000);
> >> + if (ret) {
> >> dev_err(tc->dev, "Link training timeout!\n");
> >> } else {
> >> int pattern = (value >> 11) & 0x3;
> >> int error = (value >> 8) & 0x7;
> >>
> >> dev_dbg(tc->dev,
> >> - "Link training phase %d done after %d uS:
> >> %s\n",
> >> - pattern, 1000 - timeout, errors[error]);
> >> + "Link training phase %d done: %s\n",
> >> + pattern, errors[error]);
> >
> > It's probably not a big deal in this specific case, but in general it
> > can be useful to know how long the poll took.
>
> I don't disagree, but bear in mind that the way time is measured in
> original loop assumes that tc_read, an I2C transaction over 100KHz
> bus, takes insignificant amount of time compared to 1 uS delay. I
> think original debug statement does a bit of a false advertising when
> it presents a number of polling loop iterations as if it is time it
> took to establish a link in microseconds.
>
> > Any hope to enhance regmap_read_poll_timeout() to return either the elapsed
> > time or the
> > remaining timeout instead of 0 on success ?
>
> I'd rather not go there. That'll take convincing Mark Brown to accept
> that semantics change, then fixing all of the callers across the tree
> via a separate patch series.
>
> What if instead we just add an extra debug statement before link
> training starts, so that duration of the process can be discerned from
> logging timestamps? This does require user doing a bit of math by
> hand, but it's actually more accurate timing info compared to original
> and it doesn't require any API modification.
That works for me.
--
Regards,
Laurent Pinchart
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