linux-kernel - [PATCH v3 1/2] driver core: Rework logic in __driver_deferred_probe_check_state to allow EPROBE

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Message-Id: <20200218220748.54823-1-john.stultz@linaro.org>
Date:   Tue, 18 Feb 2020 22:07:47 +0000
From:   John Stultz <john.stultz@...aro.org>
To:     lkml <linux-kernel@...r.kernel.org>
Cc:     John Stultz <john.stultz@...aro.org>,
        Rob Herring <robh@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Todd Kjos <tkjos@...gle.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pm@...r.kernel.org
Subject: [PATCH v3 1/2] driver core: Rework logic in __driver_deferred_probe_check_state to allow EPROBE_DEFER to be returned for longer

Due to commit e01afc3250255 ("PM / Domains: Stop deferring probe
at the end of initcall"), along with commit 25b4e70dcce9
("driver core: allow stopping deferred probe after init") after
late_initcall, drivers will stop getting EPROBE_DEFER, and
instead see an error causing the driver to fail to load.

That change causes trouble when trying to use many clk drivers
as modules, as the clk modules may not load until much later
after init has started. If a dependent driver loads and gets an
error instead of EPROBE_DEFER, it won't try to reload later when
the dependency is met, and will thus fail to load.

This patch reworks some of the logic in
__driver_deferred_probe_check_state() so that if the
deferred_probe_timeout value is set, we will return EPROBE_DEFER
until that timeout expires, which may be after initcalls_done
is set to true.

Specifically, on db845c, this change (when combined with booting
using deferred_probe_timeout=30) allows us to set SDM_GPUCC_845,
QCOM_CLK_RPMH and COMMON_CLK_QCOM as modules and get a working
system, where as without it the display will fail to load.

Cc: Rob Herring <robh@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Kevin Hilman <khilman@...nel.org>
Cc: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Pavel Machek <pavel@....cz>
Cc: Len Brown <len.brown@...el.com>
Cc: Todd Kjos <tkjos@...gle.com>
Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
Cc: Liam Girdwood <lgirdwood@...il.com>
Cc: Mark Brown <broonie@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-pm@...r.kernel.org
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
v2:
* Add calls to driver_deferred_probe_trigger() after the two minute timeout,
  as suggested by Bjorn
* Minor whitespace cleanups
* Switch to 30 second timeout to match what the regulator code is doing as
  suggested by Rob.
v3:
* Rework to reuse existing deferred_probe_timeout value, suggested by Rob
* Dropped Fixes: tags as Rob requested (Not my hill to die on :)
---
 drivers/base/dd.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index b25bcab2a26b..9d916a7b56a6 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -237,13 +237,12 @@ __setup("deferred_probe_timeout=", deferred_probe_timeout_setup);

 static int __driver_deferred_probe_check_state(struct device *dev)
 {
-	if (!initcalls_done)
-		return -EPROBE_DEFER;
-
-	if (!deferred_probe_timeout) {
+	if (initcalls_done && !deferred_probe_timeout) {
 		dev_WARN(dev, "deferred probe timeout, ignoring dependency");
 		return -ETIMEDOUT;
 	}
+	if (!initcalls_done || deferred_probe_timeout > 0)
+		return -EPROBE_DEFER;

 	return 0;
 }
-- 
2.17.1