Re: [PATCH 3/3] drm/i915/cx0: Clear response ready & error bit

[Gustavo Sousa <gustavo.sousa@intel.com>]

Quoting Suraj Kandpal (2025-12-30 05:31:42-03:00)
>Clear the response ready and error bit of PORT_P2M_MESSAGE_BUS_STATUS
>before writing the transaction pending bit of
>PORT_M2P_MSGBUS_CTL as that is a hard requirement. If not done
>we find that the PHY hangs since it ends up in a weird state if left
>idle for more than 1 hour.

Since the series title refers to suspend/resume, is there an easy way of
reproducing this via some power state transition?

I'm wondering if we are looking at a driver issue here or if this is
really something else.  I see that we usually call intel_cx0_bus_reset()
in error paths, which contains a call to
intel_clear_response_ready_flag(), but it could end up being not called
if the reset times out.

Do we see error messages from the driver when the PHY hangs?

--
Gustavo Sousa

>
>Bspec: 65101
>Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
>---
> drivers/gpu/drm/i915/display/intel_cx0_phy.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/drivers/gpu/drm/i915/display/intel_cx0_phy.c b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
>index 5edd293b533b..5ebc3404eee2 100644
>--- a/drivers/gpu/drm/i915/display/intel_cx0_phy.c
>+++ b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
>@@ -222,6 +222,8 @@ static int __intel_cx0_read_once(struct intel_encoder *encoder,
>                 return -ETIMEDOUT;
>         }
> 
>+        intel_clear_response_ready_flag(encoder, lane);
>+
>         intel_de_write(display, XELPDP_PORT_M2P_MSGBUS_CTL(display, port, lane),
>                        XELPDP_PORT_M2P_TRANSACTION_PENDING |
>                        XELPDP_PORT_M2P_COMMAND_READ |
>@@ -293,6 +295,8 @@ static int __intel_cx0_write_once(struct intel_encoder *encoder,
>                 return -ETIMEDOUT;
>         }
> 
>+        intel_clear_response_ready_flag(encoder, lane);
>+
>         intel_de_write(display, XELPDP_PORT_M2P_MSGBUS_CTL(display, port, lane),
>                        XELPDP_PORT_M2P_TRANSACTION_PENDING |
>                        (committed ? XELPDP_PORT_M2P_COMMAND_WRITE_COMMITTED :
>-- 
>2.34.1
>