Re: Question: Re: [PATCH] drm/bridge: analogix: protect power when get_modes or detect

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On 2016年10月12日 22:51, Sean Paul wrote:
On Wed, Oct 12, 2016 at 6:22 AM, Mark yao <mark.yao@xxxxxxxxxxxxxx> wrote:
I'm not familiar with the analogix driver, maybe use a power reference count
would better then direct power on/off analogix_dp.

Does anyone has the idea to protect detect and get_modes context?

I'm not sure a reference count is going to help here. The common
pattern is to call detect() followed by get_modes() and then modeset.
However, it's not guaranteed that any one of those functions will be
called after the other. So, if you leave things on after detect or
get_modes, you might be wasting power (or worse).

I recently ran into this exact problem with a panel we're using. Check
out "0b8b059a7: drm/bridge: analogix_dp: Ensure the panel is properly
prepared/unprepared". Perhaps you can piggyback on that function to
add your pm_runtime and plat_data callbacks (since using dpms_mode
might be racey).

Sean
Hi Sean

Thanks for your advice.

I re-test the detect and get_modes, only use pm_runtime_get/put also can fix my problem.
without plat_data callbacks can avoid race to dpms_mode.

I had send v2 patch,  you can review it.

Thanks.


I found many other connector driver also direct access register on detect or
get_modes, no problem for it?

On 2016年10月12日 18:00, Mark Yao wrote:

The drm callback ->detect and ->get_modes seems is not power safe,
they may be called when device is power off, do register access on
detect or get_modes will cause system die.

Here is the path call ->detect before analogix_dp power on
[<ffffff800843babc>] analogix_dp_detect+0x44/0xdc
[<ffffff80083fd840>]
drm_helper_probe_single_connector_modes_merge_bits+0xe8/0x41c
[<ffffff80083fdb84>] drm_helper_probe_single_connector_modes+0x10/0x18
[<ffffff8008418d24>] drm_mode_getconnector+0xf4/0x304
[<ffffff800840cff0>] drm_ioctl+0x23c/0x390
[<ffffff80081a8adc>] do_vfs_ioctl+0x4b8/0x58c
[<ffffff80081a8c10>] SyS_ioctl+0x60/0x88

Cc: Inki Dae <inki.dae@xxxxxxxxxxx>
Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
Cc: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
Cc: "Ville Syrjälä" <ville.syrjala@xxxxxxxxxxxxxxx>

Signed-off-by: Mark Yao <mark.yao@xxxxxxxxxxxxxx>
---
  drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 28
++++++++++++++++++++++
  1 file changed, 28 insertions(+)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index efac8ab..09dece2 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1062,6 +1062,13 @@ int analogix_dp_get_modes(struct drm_connector
*connector)
   return 0;
   }

+ if (dp->dpms_mode != DRM_MODE_DPMS_ON) {
+ pm_runtime_get_sync(dp->dev);
+
+ if (dp->plat_data->power_on)
+ dp->plat_data->power_on(dp->plat_data);
+ }
+
   if (analogix_dp_handle_edid(dp) == 0) {
   drm_mode_connector_update_edid_property(&dp->connector, edid);
   num_modes += drm_add_edid_modes(&dp->connector, edid);
@@ -1073,6 +1080,13 @@ int analogix_dp_get_modes(struct drm_connector
*connector)
   if (dp->plat_data->get_modes)
   num_modes += dp->plat_data->get_modes(dp->plat_data, connector);

+ if (dp->dpms_mode != DRM_MODE_DPMS_ON) {
+ if (dp->plat_data->power_off)
+ dp->plat_data->power_off(dp->plat_data);
+
+ pm_runtime_put_sync(dp->dev);
+ }
+
   ret = analogix_dp_prepare_panel(dp, false, false);
   if (ret)
   DRM_ERROR("Failed to unprepare panel (%d)\n", ret);
@@ -1106,9 +1120,23 @@ analogix_dp_detect(struct drm_connector *connector,
bool force)
   return connector_status_disconnected;
   }

+ if (dp->dpms_mode != DRM_MODE_DPMS_ON) {
+ pm_runtime_get_sync(dp->dev);
+
+ if (dp->plat_data->power_on)
+ dp->plat_data->power_on(dp->plat_data);
+ }
+
   if (!analogix_dp_detect_hpd(dp))
   status = connector_status_connected;

+ if (dp->dpms_mode != DRM_MODE_DPMS_ON) {
+ if (dp->plat_data->power_off)
+ dp->plat_data->power_off(dp->plat_data);
+
+ pm_runtime_put_sync(dp->dev);
+ }
+
   ret = analogix_dp_prepare_panel(dp, false, false);
   if (ret)
   DRM_ERROR("Failed to unprepare panel (%d)\n", ret);



--
Mark Yao




--
Mark Yao


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