2023-07-17 22:59:04

by Abhinav Kumar

Subject: [PATCH] drm: remove drm_bridge_hpd_disable() from drm_bridge_connector_destroy()

drm_bridge_hpd_enable()/drm_bridge_hpd_disable() callbacks call into
the respective driver's hpd_enable()/hpd_disable() ops. These ops control
the HPD enable/disable logic which in some cases like MSM can be a
dedicate hardware block to control the HPD.

During probe_defer cases, a connector can be initialized and then later
destroyed till the probe is retried. During connector destroy in these
cases, the hpd_disable() callback gets called without a corresponding
hpd_enable() leading to an unbalanced state potentially causing even
a crash.

This can be avoided by the respective drivers maintaining their own
state logic to ensure that a hpd_disable() without a corresponding
hpd_enable() just returns without doing anything.

However, to have a generic fix it would be better to avoid the
hpd_disable() callback from the connector destroy path and let
the hpd_enable() / hpd_disable() balance be maintained by the
corresponding drm_bridge_connector_enable_hpd() /
drm_bridge_connector_disable_hpd() APIs.

Signed-off-by: Abhinav Kumar <[email protected]>
---
drivers/gpu/drm/drm_bridge_connector.c | 6 ------
1 file changed, 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge_connector.c b/drivers/gpu/drm/drm_bridge_connector.c
index 19ae4a177ac3..3d4e25c2f3d7 100644
--- a/drivers/gpu/drm/drm_bridge_connector.c
+++ b/drivers/gpu/drm/drm_bridge_connector.c
@@ -187,12 +187,6 @@ static void drm_bridge_connector_destroy(struct drm_connector *connector)
struct drm_bridge_connector *bridge_connector =
to_drm_bridge_connector(connector);

- if (bridge_connector->bridge_hpd) {
- struct drm_bridge *hpd = bridge_connector->bridge_hpd;
-
- drm_bridge_hpd_disable(hpd);
- }
-
drm_connector_unregister(connector);
drm_connector_cleanup(connector);

--
2.40.1

2023-07-18 06:27:51

by Dmitry Baryshkov

Subject: Re: [PATCH] drm: remove drm_bridge_hpd_disable() from drm_bridge_connector_destroy()

On 18/07/2023 01:34, Abhinav Kumar wrote:
> drm_bridge_hpd_enable()/drm_bridge_hpd_disable() callbacks call into
> the respective driver's hpd_enable()/hpd_disable() ops. These ops control
> the HPD enable/disable logic which in some cases like MSM can be a
> dedicate hardware block to control the HPD.
>
> During probe_defer cases, a connector can be initialized and then later
> destroyed till the probe is retried. During connector destroy in these
> cases, the hpd_disable() callback gets called without a corresponding
> hpd_enable() leading to an unbalanced state potentially causing even
> a crash.
>
> This can be avoided by the respective drivers maintaining their own
> state logic to ensure that a hpd_disable() without a corresponding
> hpd_enable() just returns without doing anything.
>
> However, to have a generic fix it would be better to avoid the
> hpd_disable() callback from the connector destroy path and let
> the hpd_enable() / hpd_disable() balance be maintained by the
> corresponding drm_bridge_connector_enable_hpd() /
> drm_bridge_connector_disable_hpd() APIs.

Which should get called by the drm_kms_helper_disable_hpd().

Reviewed-by: Dmitry Baryshkov <[email protected]>

>
> Signed-off-by: Abhinav Kumar <[email protected]>
> ---
> drivers/gpu/drm/drm_bridge_connector.c | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_bridge_connector.c b/drivers/gpu/drm/drm_bridge_connector.c
> index 19ae4a177ac3..3d4e25c2f3d7 100644
> --- a/drivers/gpu/drm/drm_bridge_connector.c
> +++ b/drivers/gpu/drm/drm_bridge_connector.c
> @@ -187,12 +187,6 @@ static void drm_bridge_connector_destroy(struct drm_connector *connector)
> struct drm_bridge_connector *bridge_connector =
> to_drm_bridge_connector(connector);
>
> - if (bridge_connector->bridge_hpd) {
> - struct drm_bridge *hpd = bridge_connector->bridge_hpd;
> -
> - drm_bridge_hpd_disable(hpd);
> - }
> -
> drm_connector_unregister(connector);
> drm_connector_cleanup(connector);
>

--
With best wishes
Dmitry