Port D and port E GPIO loopback modes are commonly enabled via hardware
straps for use with front-panel buttons. When the BMC is powered
off or fails to boot, the front-panel buttons are directly connected to
the host chipset via the loopback to allow direct power-on and reset
control. Once the BMC has booted, the loopback mode must be disabled for
the BMC to take over control of host power-on and reset.
Disabling these loopback modes requires writing to the hardware strap
register which violates the current design of assuming the system
designer chose the strap settings for a specific reason and they should
be treated as read-only. Only the two bits of the strap register related
to these loopback modes are allowed to be written and comments have been
added to explain why.
Signed-off-by: Rick Altherr <ralth...@google.com>
---
drivers/pinctrl/aspeed/pinctrl-aspeed.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/drivers/pinctrl/aspeed/pinctrl-aspeed.c
b/drivers/pinctrl/aspeed/pinctrl-aspeed.c
index 76f62bd45f02..5b49952e5fad 100644
--- a/drivers/pinctrl/aspeed/pinctrl-aspeed.c
+++ b/drivers/pinctrl/aspeed/pinctrl-aspeed.c
@@ -198,9 +198,19 @@ static int aspeed_sig_expr_set(const struct
aspeed_sig_expr *expr,
* them. This may mean that certain functions cannot be
* deconfigured and is the reason we re-evaluate after writing
* all descriptor bits.
+ *
+ * Port D and port E GPIO loopback modes are the only exception
+ * as those are commonly used with front-panel buttons to allow
+ * normal operation of the host when the BMC is powered off or
+ * fails to boot. Once the BMC has booted, the loopback mode
+ * must be disabled for the BMC to control host power-on and
+ * reset.
*/
- if ((desc->reg == HW_STRAP1 || desc->reg == HW_STRAP2) &&
- desc->ip == ASPEED_IP_SCU)
+ if (desc->ip == ASPEED_IP_SCU && desc->reg == HW_STRAP1 &&
+ !(desc->mask & (BIT(21) | BIT(22))))
+ continue;
+
+ if (desc->ip == ASPEED_IP_SCU && desc->reg == HW_STRAP2)
continue;
ret = regmap_update_bits(maps[desc->ip], desc->reg,
--
2.11.0.483.g087da7b7c-goog
