[PATCH] remoteproc: mediatek: Break lock dependency to `prepare_lock`

[Tzung-Bi Shih <tzungbi@kernel.org>]

`scp_ipi_send` acquires `prepare_lock` via `clk_prepare_enable` while
the caller often holds `ec_dev->lock` (e.g., `cros_ec_cmd_xfer`).  The
reverse dependency exists where `clk_prepare` can trigger operations
that eventually take `ec_dev->lock` (e.g., via sysfs/regulator/genpd).

Move clock prepare / unprepare operations to remoteproc prepare() /
unprepare() callbacks to break the lock dependency from `ec_dev->lock`
to `prepare_lock`.

This breaks the dependency chain in the lockdep report:
> WARNING: possible circular locking dependency detected
> ...
> the existing dependency chain (in reverse order) is:
> ...
> -> #0 (prepare_lock){+.+.}-{3:3}:
>        __lock_acquire
>        lock_acquire
>        __mutex_lock_common
>        mutex_lock_nested
>        clk_prepare
>        scp_ipi_send [mtk_scp_ipi]
>        scp_send_ipi [mtk_scp]
>        mtk_rpmsg_send [mtk_rpmsg]
>        rpmsg_send [rpmsg_core]
>        cros_ec_pkt_xfer_rpmsg [cros_ec_rpmsg]

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
 drivers/remoteproc/mtk_scp.c     | 39 +++++++++++++++++++++++---------
 drivers/remoteproc/mtk_scp_ipi.c |  4 ++--
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/drivers/remoteproc/mtk_scp.c b/drivers/remoteproc/mtk_scp.c
index db8fd045468d..98d00bd5200c 100644
--- a/drivers/remoteproc/mtk_scp.c
+++ b/drivers/remoteproc/mtk_scp.c
@@ -283,7 +283,7 @@ static irqreturn_t scp_irq_handler(int irq, void *priv)
 	struct mtk_scp *scp = priv;
 	int ret;
 
-	ret = clk_prepare_enable(scp->clk);
+	ret = clk_enable(scp->clk);
 	if (ret) {
 		dev_err(scp->dev, "failed to enable clocks\n");
 		return IRQ_NONE;
@@ -291,7 +291,7 @@ static irqreturn_t scp_irq_handler(int irq, void *priv)
 
 	scp->data->scp_irq_handler(scp);
 
-	clk_disable_unprepare(scp->clk);
+	clk_disable(scp->clk);
 
 	return IRQ_HANDLED;
 }
@@ -665,7 +665,7 @@ static int scp_load(struct rproc *rproc, const struct firmware *fw)
 	struct device *dev = scp->dev;
 	int ret;
 
-	ret = clk_prepare_enable(scp->clk);
+	ret = clk_enable(scp->clk);
 	if (ret) {
 		dev_err(dev, "failed to enable clocks\n");
 		return ret;
@@ -680,7 +680,7 @@ static int scp_load(struct rproc *rproc, const struct firmware *fw)
 
 	ret = scp_elf_load_segments(rproc, fw);
 leave:
-	clk_disable_unprepare(scp->clk);
+	clk_disable(scp->clk);
 
 	return ret;
 }
@@ -691,14 +691,14 @@ static int scp_parse_fw(struct rproc *rproc, const struct firmware *fw)
 	struct device *dev = scp->dev;
 	int ret;
 
-	ret = clk_prepare_enable(scp->clk);
+	ret = clk_enable(scp->clk);
 	if (ret) {
 		dev_err(dev, "failed to enable clocks\n");
 		return ret;
 	}
 
 	ret = scp_ipi_init(scp, fw);
-	clk_disable_unprepare(scp->clk);
+	clk_disable(scp->clk);
 	return ret;
 }
 
@@ -709,7 +709,7 @@ static int scp_start(struct rproc *rproc)
 	struct scp_run *run = &scp->run;
 	int ret;
 
-	ret = clk_prepare_enable(scp->clk);
+	ret = clk_enable(scp->clk);
 	if (ret) {
 		dev_err(dev, "failed to enable clocks\n");
 		return ret;
@@ -734,14 +734,14 @@ static int scp_start(struct rproc *rproc)
 		goto stop;
 	}
 
-	clk_disable_unprepare(scp->clk);
+	clk_disable(scp->clk);
 	dev_info(dev, "SCP is ready. FW version %s\n", run->fw_ver);
 
 	return 0;
 
 stop:
 	scp->data->scp_reset_assert(scp);
-	clk_disable_unprepare(scp->clk);
+	clk_disable(scp->clk);
 	return ret;
 }
 
@@ -909,7 +909,7 @@ static int scp_stop(struct rproc *rproc)
 	struct mtk_scp *scp = rproc->priv;
 	int ret;
 
-	ret = clk_prepare_enable(scp->clk);
+	ret = clk_enable(scp->clk);
 	if (ret) {
 		dev_err(scp->dev, "failed to enable clocks\n");
 		return ret;
@@ -917,12 +917,29 @@ static int scp_stop(struct rproc *rproc)
 
 	scp->data->scp_reset_assert(scp);
 	scp->data->scp_stop(scp);
-	clk_disable_unprepare(scp->clk);
+	clk_disable(scp->clk);
 
 	return 0;
 }
 
+static int scp_prepare(struct rproc *rproc)
+{
+	struct mtk_scp *scp = rproc->priv;
+
+	return clk_prepare(scp->clk);
+}
+
+static int scp_unprepare(struct rproc *rproc)
+{
+	struct mtk_scp *scp = rproc->priv;
+
+	clk_unprepare(scp->clk);
+	return 0;
+}
+
 static const struct rproc_ops scp_ops = {
+	.prepare	= scp_prepare,
+	.unprepare	= scp_unprepare,
 	.start		= scp_start,
 	.stop		= scp_stop,
 	.load		= scp_load,
diff --git a/drivers/remoteproc/mtk_scp_ipi.c b/drivers/remoteproc/mtk_scp_ipi.c
index c068227e251e..7a37e273b3af 100644
--- a/drivers/remoteproc/mtk_scp_ipi.c
+++ b/drivers/remoteproc/mtk_scp_ipi.c
@@ -171,7 +171,7 @@ int scp_ipi_send(struct mtk_scp *scp, u32 id, void *buf, unsigned int len,
 	    WARN_ON(len > scp_sizes->ipi_share_buffer_size) || WARN_ON(!buf))
 		return -EINVAL;
 
-	ret = clk_prepare_enable(scp->clk);
+	ret = clk_enable(scp->clk);
 	if (ret) {
 		dev_err(scp->dev, "failed to enable clock\n");
 		return ret;
@@ -211,7 +211,7 @@ int scp_ipi_send(struct mtk_scp *scp, u32 id, void *buf, unsigned int len,
 
 unlock_mutex:
 	mutex_unlock(&scp->send_lock);
-	clk_disable_unprepare(scp->clk);
+	clk_disable(scp->clk);
 
 	return ret;
 }
-- 
2.52.0.351.gbe84eed79e-goog