Re: [PATCH] drm/i915: Prevent kernel panic on reading out compliance debugfs files

[Manasi Navare <manasi.d.navare@intel.com>]

Thanks fo rthis patch Maarten. I had noticed this while running the intel_dp_compliance
IGT tool. But I saw this with DP SST systems as well. What could be happening in that case?

Manasi

On Wed, Jun 21, 2017 at 12:59:41PM +0200, Maarten Lankhorst wrote:
> When reading all debugfs files on a system with DP-MST the kernel panics
> on a null pointer dereference because intel_dp is null for a DP-MST
> connector. Detect this case and skip those connectors.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 33 ++++++++++++++++++++++++---------
>  1 file changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 1f1176b6400e..30e2e168fe92 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -3812,13 +3812,18 @@ static int i915_displayport_test_active_show(struct seq_file *m, void *data)
>  
>  	drm_connector_list_iter_begin(dev, &conn_iter);
>  	drm_for_each_connector_iter(connector, &conn_iter) {
> +		struct intel_encoder *encoder;
> +
>  		if (connector->connector_type !=
>  		    DRM_MODE_CONNECTOR_DisplayPort)
>  			continue;
>  
> -		if (connector->status == connector_status_connected &&
> -		    connector->encoder != NULL) {
> -			intel_dp = enc_to_intel_dp(connector->encoder);
> +		encoder = to_intel_encoder(connector->encoder);
> +		if (encoder && encoder->type == INTEL_OUTPUT_DP_MST)
> +			continue;
> +
> +		if (encoder && connector->status == connector_status_connected) {
> +			intel_dp = enc_to_intel_dp(&encoder->base);
>  			if (intel_dp->compliance.test_active)
>  				seq_puts(m, "1");
>  			else
> @@ -3858,13 +3863,18 @@ static int i915_displayport_test_data_show(struct seq_file *m, void *data)
>  
>  	drm_connector_list_iter_begin(dev, &conn_iter);
>  	drm_for_each_connector_iter(connector, &conn_iter) {
> +		struct intel_encoder *encoder;
> +
>  		if (connector->connector_type !=
>  		    DRM_MODE_CONNECTOR_DisplayPort)
>  			continue;
>  
> -		if (connector->status == connector_status_connected &&
> -		    connector->encoder != NULL) {
> -			intel_dp = enc_to_intel_dp(connector->encoder);
> +		encoder = to_intel_encoder(connector->encoder);
> +		if (encoder && encoder->type == INTEL_OUTPUT_DP_MST)
> +			continue;
> +
> +		if (encoder && connector->status == connector_status_connected) {
> +			intel_dp = enc_to_intel_dp(&encoder->base);
>  			if (intel_dp->compliance.test_type ==
>  			    DP_TEST_LINK_EDID_READ)
>  				seq_printf(m, "%lx",
> @@ -3911,13 +3921,18 @@ static int i915_displayport_test_type_show(struct seq_file *m, void *data)
>  
>  	drm_connector_list_iter_begin(dev, &conn_iter);
>  	drm_for_each_connector_iter(connector, &conn_iter) {
> +		struct intel_encoder *encoder;
> +
>  		if (connector->connector_type !=
>  		    DRM_MODE_CONNECTOR_DisplayPort)
>  			continue;
>  
> -		if (connector->status == connector_status_connected &&
> -		    connector->encoder != NULL) {
> -			intel_dp = enc_to_intel_dp(connector->encoder);
> +		encoder = to_intel_encoder(connector->encoder);
> +		if (encoder && encoder->type == INTEL_OUTPUT_DP_MST)
> +			continue;
> +
> +		if (encoder && connector->status == connector_status_connected) {
> +			intel_dp = enc_to_intel_dp(&encoder->base);
>  			seq_printf(m, "%02lx", intel_dp->compliance.test_type);
>  		} else
>  			seq_puts(m, "0");
> -- 
> 2.11.0
> 
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