[PATCH] [RFC] soc: imx: imx8m-blk-ctrl: Split clock prepare from clock enable in the domain

[Marek Vasut]

It is possible for clk_disable_unused() to trigger lockdep warning
regarding lock ordering in this driver. This happens in case of the
following conditions:

A) clock core clk_disable_unused() triggers the following sequence in a
   driver which also uses blkctrl domain:
   - clk_prepare_lock() -> obtains clock core prepare_lock
   - pm_runtime_get*() -> obtains &blk_ctrl_genpd_lock_class

B) driver powers up a power domain and triggers the following sequence
   in blkctrl:
   - pm_runtime_get_sync() -> obtains &blk_ctrl_genpd_lock_class
   - clk_bulk_prepare_enable() -> obtains clock core prepare_lock

This can lead to a deadlock in case A and B runs on separate CPUs.

To avoid the deadlock, split clk_*prepare() from clk_*enable() and
call the former before pm_runtime_get_sync(). This way, the blkctrl
driver always claims the prepare_lock before blk_ctrl_genpd_lock_class
and the deadlock is avoided.

Signed-off-by: Marek Vasut <marex at denx.de>
---
Cc: Fabio Estevam <festevam at denx.de>
Cc: Jacky Bai <ping.bai at nxp.com>
Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Cc: Lucas Stach <l.stach at pengutronix.de>
Cc: Peng Fan <peng.fan at nxp.com>
Cc: Shawn Guo <shawnguo at kernel.org>
Cc: Shengjiu Wang <shengjiu.wang at nxp.com>
Cc: Stephen Boyd <sboyd at kernel.org>
Cc: linux-clk at vger.kernel.org
Cc: linux-imx at nxp.com
To: linux-arm-kernel at lists.infradead.org
---
 drivers/soc/imx/imx8mp-blk-ctrl.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/soc/imx/imx8mp-blk-ctrl.c b/drivers/soc/imx/imx8mp-blk-ctrl.c
index b7d4161fcda9c..571c98b5b005b 100644
--- a/drivers/soc/imx/imx8mp-blk-ctrl.c
+++ b/drivers/soc/imx/imx8mp-blk-ctrl.c
@@ -393,15 +393,21 @@ static int imx8mp_blk_ctrl_power_on(struct generic_pm_domain *genpd)
 	struct imx8mp_blk_ctrl *bc = domain->bc;
 	int ret;
 
+	ret = clk_bulk_prepare(data->num_clks, domain->clks);
+	if (ret) {
+		dev_err(bc->dev, "failed to enable clocks\n");
+		return ret;
+	}
+
 	/* make sure bus domain is awake */
 	ret = pm_runtime_resume_and_get(bc->bus_power_dev);
 	if (ret < 0) {
 		dev_err(bc->dev, "failed to power up bus domain\n");
-		return ret;
+		goto rpm_put;
 	}
 
 	/* enable upstream clocks */
-	ret = clk_bulk_prepare_enable(data->num_clks, domain->clks);
+	ret = clk_bulk_enable(data->num_clks, domain->clks);
 	if (ret) {
 		dev_err(bc->dev, "failed to enable clocks\n");
 		goto bus_put;
@@ -426,9 +432,11 @@ static int imx8mp_blk_ctrl_power_on(struct generic_pm_domain *genpd)
 	return 0;
 
 clk_disable:
-	clk_bulk_disable_unprepare(data->num_clks, domain->clks);
+	clk_bulk_disable(data->num_clks, domain->clks);
 bus_put:
 	pm_runtime_put(bc->bus_power_dev);
+rpm_put:
+	clk_bulk_unprepare(data->num_clks, domain->clks);
 
 	return ret;
 }
-- 
2.35.1