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

[Sean Paul]

On Wed, Oct 12, 2016 at 6:22 AM, Mark yao <mark.yao at rock-chips.com> 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


> 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 at samsung.com>
> Cc: Sean Paul <seanpaul at chromium.org>
> Cc: Gustavo Padovan <gustavo.padovan at collabora.co.uk>
> Cc: "Ville Syrjälä" <ville.syrjala at linux.intel.com>
>
> Signed-off-by: Mark Yao <mark.yao at rock-chips.com>
> ---
>  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