[PATCH v7 2/3] remoteproc: imx_rproc: skip clock enable when M-core is managed by the SCU

[Hiago De Franco <hiagofranco@gmail.com>]

From: Hiago De Franco <hiago.franco@toradex.com>

For the i.MX8X and i.MX8 family SoCs, when the Cortex-M core is powered
up and started by the Cortex-A core using the bootloader (e.g., via the
U-Boot bootaux command), both M-core and Linux run within the same SCFW
(System Controller Firmware) partition. With that, Linux has permission
to control the M-core.

But once the M-core is started by the bootloader, the SCFW automatically
enables its clock and sets the clock rate. If Linux later attempts to
enable the same clock via clk_prepare_enable(), the SCFW returns a
'LOCKED' error, as the clock is already configured by the SCFW. This
causes the probe function in imx_rproc.c to fail, leading to the M-core
power domain being shut down while the core is still running. This
results in a fault from the SCU (System Controller Unit) and triggers a
system reset.

To address this issue, ignore handling the clk for i.MX8X and i.MX8
M-core, as SCFW already takes care of enabling and configuring the
clock.

Suggested-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Hiago De Franco <hiago.franco@toradex.com>
---
v6 -> v7:
 - Added Peng reviewed-by.
v5 -> v6:
 - Commit description improved, as suggested.
v4 -> v5:
 - Unchanged.
v3 -> v4:
 - Unchanged.
v2 -> v3:
 - Unchanged.
v1 -> v2:
 - Commit description updated, as suggested. Fixed Peng Fan email.
---
 drivers/remoteproc/imx_rproc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/remoteproc/imx_rproc.c b/drivers/remoteproc/imx_rproc.c
index 74299af1d7f1..627e57a88db2 100644
--- a/drivers/remoteproc/imx_rproc.c
+++ b/drivers/remoteproc/imx_rproc.c
@@ -1029,8 +1029,8 @@ static int imx_rproc_clk_enable(struct imx_rproc *priv)
 	struct device *dev = priv->dev;
 	int ret;
 
-	/* Remote core is not under control of Linux */
-	if (dcfg->method == IMX_RPROC_NONE)
+	/* Remote core is not under control of Linux or it is managed by SCU API */
+	if (dcfg->method == IMX_RPROC_NONE || dcfg->method == IMX_RPROC_SCU_API)
 		return 0;
 
 	priv->clk = devm_clk_get(dev, NULL);
-- 
2.39.5