[PATCH v8 04/21] drm/bridge: synopsys: dw-dp: Document missing reset line deassert

[Sebastian Reichel]

If the driver uses devm_reset_control_get_exclusive_deasserted() instead
of devm_reset_control_get() and thus automatically deasserts during
probe, the SoC will hang when the device is unbound.

This does not happen, when runtime PM is being used (not yet supported
in mainline), which suggests the power-domain involved requires this reset
line to be deasserted.

Even with runtime PM there is no gurantee that the power-domain is
disabled as it is shared. Considering the power-domain does not have
the reset dependency described in DT, document the problem but leave
things in the current state until a better solution is found as the
reset line is deasserted by default on all supported platforms.

Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Signed-off-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/bridge/synopsys/dw-dp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
index 6289ed06e231..a8ae13cf91d6 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
@@ -2076,6 +2076,10 @@ struct dw_dp *dw_dp_probe(struct platform_device *pdev, const struct dw_dp_plat_
 		return ERR_CAST(dp->hdcp_clk);
 	}
 
+	/*
+	 * This reset line is deasserted by default; asserting it hangs the SoC if the
+	 * related power-domain is still active.
+	 */
 	dp->rstc = devm_reset_control_get(dev, NULL);
 	if (IS_ERR(dp->rstc)) {
 		dev_err_probe(dev, PTR_ERR(dp->rstc), "failed to get reset control\n");

-- 
2.53.0