[PATCH 1/3] clk: Add __clk_disable_unprepare_counts_only() helper

[Hans de Goede <johannes.goede@oss.qualcomm.com>]

The device-tree simple-framebuffer device is special in that it does not
describe actual hardware, but it allows firmware (e.g. u-boot) to pass a
firmware initialized framebuffer to the OS to use as display during boot.

To avoid clocks used by the firmware framebuffer getting touched while in
use, the DT node contains a list of clocks and the simpledrm driver calls
clk_prepare_enable() on these clocks. When the real display driver loads
simpledrm gets unbound and calls clk_disable_unprepare().

The simple-framebuffer concept assumes that the order in which resources
are acquired does not matter since they are already on, so power-sequencing
is not an issue. But clk_disable_unprepare() actually turns the clock off,
messing with the hardware state before the real display driver loads,
without any knowledge of the proper power-off sequence for the display.

Sometimes this leaves the hardware in an undefined state e.g. on some
Qualcomm platforms turning off the DP clocks at simpledrm remove() results
in the following error when the msm display driver tries to re-enable them:

[    2.980181] disp_cc_mdss_dptx3_pixel0_clk_src: rcg didn't update its configuration.
[    2.980272] WARNING: drivers/clk/qcom/clk-rcg2.c:136 at update_config+0xdc/0x100

Clocks from the simple-framebuffer DT node are not so much clocks which
the simpledrm driver should take full control of, but rather are clocks
which should not be touched as long as the firmware framebuffer is in use.
This includes not turning them off before handing over control to the real
display driver.

Add a new __clk_disable_unprepare_counts_only() helper which decrements the
enable, prepare and protect counts of the clock and its parents, so that
the real display can take control over the clocks, but which does not
actually disable any clocks.

Signed-off-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
---
 drivers/clk/clk.c   | 41 +++++++++++++++++++++++++++++------------
 include/linux/clk.h | 14 ++++++++++++++
 2 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 47093cda9df3..8c92d3551556 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1037,7 +1037,7 @@ int devm_clk_rate_exclusive_get(struct device *dev, struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(devm_clk_rate_exclusive_get);
 
-static void clk_core_unprepare(struct clk_core *core)
+static void clk_core_unprepare(struct clk_core *core, bool call_unprepare_op)
 {
 	lockdep_assert_held(&prepare_lock);
 
@@ -1062,18 +1062,18 @@ static void clk_core_unprepare(struct clk_core *core)
 
 	trace_clk_unprepare(core);
 
-	if (core->ops->unprepare)
+	if (call_unprepare_op && core->ops->unprepare)
 		core->ops->unprepare(core->hw);
 
 	trace_clk_unprepare_complete(core);
-	clk_core_unprepare(core->parent);
+	clk_core_unprepare(core->parent, call_unprepare_op);
 	clk_pm_runtime_put(core);
 }
 
 static void clk_core_unprepare_lock(struct clk_core *core)
 {
 	clk_prepare_lock();
-	clk_core_unprepare(core);
+	clk_core_unprepare(core, true);
 	clk_prepare_unlock();
 }
 
@@ -1140,7 +1140,7 @@ static int clk_core_prepare(struct clk_core *core)
 
 	return 0;
 unprepare:
-	clk_core_unprepare(core->parent);
+	clk_core_unprepare(core->parent, true);
 runtime_put:
 	clk_pm_runtime_put(core);
 	return ret;
@@ -1178,7 +1178,7 @@ int clk_prepare(struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(clk_prepare);
 
-static void clk_core_disable(struct clk_core *core)
+static void clk_core_disable(struct clk_core *core, bool call_disable_op)
 {
 	lockdep_assert_held(&enable_lock);
 
@@ -1197,12 +1197,12 @@ static void clk_core_disable(struct clk_core *core)
 
 	trace_clk_disable(core);
 
-	if (core->ops->disable)
+	if (call_disable_op && core->ops->disable)
 		core->ops->disable(core->hw);
 
 	trace_clk_disable_complete(core);
 
-	clk_core_disable(core->parent);
+	clk_core_disable(core->parent, call_disable_op);
 }
 
 static void clk_core_disable_lock(struct clk_core *core)
@@ -1210,7 +1210,7 @@ static void clk_core_disable_lock(struct clk_core *core)
 	unsigned long flags;
 
 	flags = clk_enable_lock();
-	clk_core_disable(core);
+	clk_core_disable(core, true);
 	clk_enable_unlock(flags);
 }
 
@@ -1235,6 +1235,23 @@ void clk_disable(struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(clk_disable);
 
+void __clk_disable_unprepare_counts_only(struct clk *clk)
+{
+	unsigned long flags;
+
+	if (IS_ERR_OR_NULL(clk))
+		return;
+
+	flags = clk_enable_lock();
+	clk_core_disable(clk->core, false);
+	clk_enable_unlock(flags);
+
+	clk_prepare_lock();
+	clk_core_unprepare(clk->core, false);
+	clk_prepare_unlock();
+}
+EXPORT_SYMBOL_GPL(__clk_disable_unprepare_counts_only);
+
 static int clk_core_enable(struct clk_core *core)
 {
 	int ret = 0;
@@ -1262,7 +1279,7 @@ static int clk_core_enable(struct clk_core *core)
 		trace_clk_enable_complete(core);
 
 		if (ret) {
-			clk_core_disable(core->parent);
+			clk_core_disable(core->parent, true);
 			return ret;
 		}
 	}
@@ -2451,7 +2468,7 @@ static void clk_change_rate(struct clk_core *core)
 
 	if (core->flags & CLK_SET_RATE_UNGATE) {
 		clk_core_disable_lock(core);
-		clk_core_unprepare(core);
+		clk_core_unprepare(core, true);
 	}
 
 	if (core->flags & CLK_OPS_PARENT_ENABLE)
@@ -4063,7 +4080,7 @@ static int __clk_core_init(struct clk_core *core)
 		if (ret) {
 			pr_warn("%s: critical clk '%s' failed to enable\n",
 			       __func__, core->name);
-			clk_core_unprepare(core);
+			clk_core_unprepare(core, true);
 			goto out;
 		}
 	}
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 998ba3f261da..7dee0dbb9018 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -783,6 +783,19 @@ void clk_disable(struct clk *clk);
  */
 void clk_bulk_disable(int num_clks, const struct clk_bulk_data *clks);
 
+/**
+ * __clk_disable_unprepare_counts_only - Decrement enable and prepare counts
+ *
+ * Like clk_disable_unprepare() but then only decrement the enable, prepare and
+ * protect counts of the clock and its parents without actually disabling any
+ * clocks.
+ *
+ * This function should only be used in special case where the clocks should
+ * stay on while handing control over from an early-boot driver like simpledrm
+ * to a later more featureful driver. When in doubt do NOT use this function.
+ */
+void __clk_disable_unprepare_counts_only(struct clk *clk);
+
 /**
  * clk_get_rate - obtain the current clock rate (in Hz) for a clock source.
  *		  This is only valid once the clock source has been enabled.
@@ -1099,6 +1112,7 @@ static inline int __must_check clk_bulk_enable(int num_clks,
 
 static inline void clk_disable(struct clk *clk) {}
 
+static inline void __clk_disable_unprepare_counts_only(struct clk *clk) {}
 
 static inline void clk_bulk_disable(int num_clks,
 				    const struct clk_bulk_data *clks) {}
-- 
2.54.0