[Intel-gfx] [PATCH v3] drm/i915/hdcp: Update CP as per the kernel internal state

[Jani Nikula]

On Mon, 20 Jan 2020, Anshuman Gupta <anshuman.gupta at intel.com> wrote:
> Content Protection property should be updated as per the kernel
> internal state. Let's say if Content protection is disabled
> by userspace, CP property should be set to UNDESIRED so that
> reauthentication will not happen until userspace request it again,
> but when kernel disables the HDCP due to any DDI disabling sequences
> like modeset/DPMS operation, kernel should set the property to
> DESIRED, so that when opportunity arises, kernel will start the
> HDCP authentication on its own.
>
> Somewhere in the line, state machine to set content protection to
> DESIRED from kernel was broken and IGT coverage was missing for it.
> This patch fixes it.
> IGT patch to catch further regression on this features is being
> worked upon.
>
> v2:
>  - Incorporated the necessary locking. (Ram)
>  - Set content protection property to CP_DESIRED only when
>    user has not asked explicitly to set CP_UNDESIRED.
>
> v3:
>  - Reset the is_hdcp_undesired flag to false. (Ram)
>  - Rephrasing commit log and small comment for is_hdcp_desired
>    flag. (Ram)
>
> CC: Ramalingam C <ramalingam.c at intel.com>
> Reviewed-by: Ramalingam C <ramalingam.c at intel.com>
> Signed-off-by: Anshuman Gupta <anshuman.gupta at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display_types.h |  6 ++++++
>  drivers/gpu/drm/i915/display/intel_hdcp.c          | 13 ++++++++++++-
>  2 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 630a94892b7b..401a9a7689fb 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -345,6 +345,12 @@ struct intel_hdcp {
>  	struct delayed_work check_work;
>  	struct work_struct prop_work;
>  
> +	/*
> +	 * Flag to differentiate that HDCP is being disabled originated from
> +	 * userspace or triggered from kernel DDI disable sequence.
> +	 */
> +	bool is_hdcp_undesired;
> +

First, the comment and the name of the member don't align. The member
name does not explain what it is, and you absolutely need to look at the
comment for it to make sense in code.

>  	/* HDCP1.4 Encryption status */
>  	bool hdcp_encrypted;
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
> index 0fdbd39f6641..7f631ebd8395 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
> @@ -2002,11 +2002,18 @@ int intel_hdcp_disable(struct intel_connector *connector)
>  	mutex_lock(&hdcp->mutex);
>  
>  	if (hdcp->value != DRM_MODE_CONTENT_PROTECTION_UNDESIRED) {
> -		hdcp->value = DRM_MODE_CONTENT_PROTECTION_UNDESIRED;
>  		if (hdcp->hdcp2_encrypted)
>  			ret = _intel_hdcp2_disable(connector);
>  		else if (hdcp->hdcp_encrypted)
>  			ret = _intel_hdcp_disable(connector);
> +
> +		if (hdcp->is_hdcp_undesired) {
> +			hdcp->value = DRM_MODE_CONTENT_PROTECTION_UNDESIRED;
> +			hdcp->is_hdcp_undesired = false;
> +		} else {
> +			hdcp->value = DRM_MODE_CONTENT_PROTECTION_DESIRED;
> +			schedule_work(&hdcp->prop_work);
> +		}

Second, all the places you call intel_hdcp_disable() from have access to
the connector state, so IIUC you could deduce the state from there and
pass it to intel_hdcp_disable() without having to add another
flag/sub-state such as ->is_hdcp_undesired.

Third, reading the code, I am not sure I fully appreciate why there is a
duplicated hdcp->value, instead of using the content_protection member
from connector state to begin with. Between those two and the one added
in this patch, looks like there's a lot of state that could go out of
sync.

>  	}
>  
>  	mutex_unlock(&hdcp->mutex);
> @@ -2044,6 +2051,7 @@ void intel_hdcp_atomic_check(struct drm_connector *connector,
>  {
>  	u64 old_cp = old_state->content_protection;
>  	u64 new_cp = new_state->content_protection;
> +	struct intel_connector *intel_conn = to_intel_connector(connector);
>  	struct drm_crtc_state *crtc_state;
>  
>  	if (!new_state->crtc) {
> @@ -2069,6 +2077,9 @@ void intel_hdcp_atomic_check(struct drm_connector *connector,
>  			return;
>  	}
>  
> +	if (new_cp == DRM_MODE_CONTENT_PROTECTION_UNDESIRED)
> +		intel_conn->hdcp.is_hdcp_undesired  =  true;
> +

Finally, this underlines the above points. If atomic check fails later
for some unrelated reason, you've still ended up changing the
connector. You'll tell userspace things failed, but mysteriously things
will change anyway. It is almost never a good idea to add more state
variables if you can figure the same thing from the single point of
truth.

BR,
Jani.


>  	crtc_state = drm_atomic_get_new_crtc_state(new_state->state,
>  						   new_state->crtc);
>  	crtc_state->mode_changed = true;

-- 
Jani Nikula, Intel Open Source Graphics Center