soc: imx: imx93-blk-ctrl: Add dedicated lockdep class for nested genpd locks

This is the same approach as being used within imx8mp-blk-ctrl. This fixes
the lockdep warning about 'possible recursive locking detected' with the
following (reduced) backtrace:
genpd_lock_mtx+0x14/0x1c
genpd_runtime_resume+0x108/0x308
__rpm_callback+0x44/0x19c
rpm_callback+0x64/0x70
rpm_resume+0x438/0x6d8
__pm_runtime_resume+0x54/0xb0
imx93_blk_ctrl_power_on+0x100/0x294
_genpd_power_on+0x8c/0x16c
genpd_power_on.part.0+0xa0/0x1a0
__genpd_dev_pm_attach+0x14c/0x2e4
genpd_dev_pm_attach+0x58/0x64
dev_pm_domain_attach+0x1c/0x2c
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

drivers/soc/imx/imx93-blk-ctrl.c

@@ -187,6 +187,8 @@ static int imx93_blk_ctrl_power_off(struct generic_pm_domain *genpd)
 	return 0;
 }
 
+static struct lock_class_key blk_ctrl_genpd_lock_class;
+
 static int imx93_blk_ctrl_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -269,6 +271,19 @@ static int imx93_blk_ctrl_probe(struct platform_device *pdev)
 			goto cleanup_pds;
 		}
 
+		/*
+		 * We use runtime PM to trigger power on/off of the upstream GPC
+		 * domain, as a strict hierarchical parent/child power domain
+		 * setup doesn't allow us to meet the sequencing requirements.
+		 * This means we have nested locking of genpd locks, without the
+		 * nesting being visible at the genpd level, so we need a
+		 * separate lock class to make lockdep aware of the fact that
+		 * this are separate domain locks that can be nested without a
+		 * self-deadlock.
+		 */
+		lockdep_set_class(&domain->genpd.mlock,
+				  &blk_ctrl_genpd_lock_class);
+
 		bc->onecell_data.domains[i] = &domain->genpd;
 	}