Re: [PATCH v6] drm/i915/dsc: Add Per connector debugfs node for DSC support/enable

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

On Wed, Dec 05, 2018 at 02:00:39PM -0500, Lyude Paul wrote:
> Looks good, some small nitpicks
> 
> On Tue, 2018-12-04 at 11:55 -0800, Manasi Navare wrote:
> > DSC can be supported per DP connector. This patch adds a per connector
> > debugfs node to expose DSC support capability by the kernel.
> > The same node can be used from userspace to force DSC enable.
> > 
> > force_dsc_en written through this debugfs node is used to force
> > DSC even for lower resolutions.
> > 
> > v6:
> > * Read fec_capable only for non edp (Manasi)
> > v5:
> > * Name it dsc sink support and also add
> > fec support in the same node (Ville)
> > v4:
> > * Add missed connector_status check (Manasi)
> > * Create i915_dsc_support node only for Gen >=10 (manasi)
> > * Access intel_dp->dsc_dpcd only if its not NULL (Manasi)
> > v3:
> > * Combine Force_dsc_en with this patch (Ville)
> > v2:
> > * Use kstrtobool_from_user to avoid explicit error checking (Lyude)
> > * Rebase on drm-tip (Manasi)
> > 
> > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> > Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
> > Cc: Lyude Paul <lyude@redhat.com>
> > Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_debugfs.c | 80 +++++++++++++++++++++++++++++
> >  drivers/gpu/drm/i915/intel_dp.c     |  3 +-
> >  drivers/gpu/drm/i915/intel_drv.h    |  3 ++
> >  3 files changed, 85 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
> > b/drivers/gpu/drm/i915/i915_debugfs.c
> > index 129b9a6f8309..ec10ab027d18 100644
> > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> > @@ -5086,6 +5086,79 @@ static int i915_hdcp_sink_capability_show(struct
> > seq_file *m, void *data)
> >  }
> >  DEFINE_SHOW_ATTRIBUTE(i915_hdcp_sink_capability);
> >  
> > +static int i915_dsc_fec_support_show(struct seq_file *m, void *data)
> > +{
> > +	struct drm_connector *connector = m->private;
> > +	struct intel_encoder *encoder = intel_attached_encoder(connector);
> > +	struct intel_dp *intel_dp =
> > +		enc_to_intel_dp(&encoder->base);
> > +	struct intel_crtc *crtc;
> > +	struct intel_crtc_state *crtc_state;
> > +
> > +	if (connector->status != connector_status_connected)
> > +		return -ENODEV;
> > +
> > +	crtc = to_intel_crtc(encoder->base.crtc);
> > +	crtc_state = to_intel_crtc_state(crtc->base.state);

I am seeing a kernel NULl pointer dereferencing here in CI possibly because
the crtc is NULL and as per Ville and Danvet I should be grabbing both connection mutex
and crtc mutex and use the acquire ctx and backoff stuff so I am trying to understand that part
and seeing how I can use that.

Let me know if you have any inputs/examples on that too..

> > +	drm_modeset_lock(&crtc->base.mutex, NULL);
> > +	seq_printf(m, "DSC_Enabled: %s\n",
> > +		   yesno(crtc_state->dsc_params.compression_enable));
> > +	if (intel_dp->dsc_dpcd)
> > +		seq_printf(m, "DSC_Sink_Support: %s\n",
> > +			   yesno(drm_dp_sink_supports_dsc(intel_dp-
> > >dsc_dpcd)));
> > +	if (!intel_dp_is_edp(intel_dp))
> > +		seq_printf(m, "FEC_Sink_Support: %s\n",
> > +			   yesno(drm_dp_sink_supports_fec(intel_dp-
> > >fec_capable)));
> > +	drm_modeset_unlock(&crtc->base.mutex);
> > +
> > +	return 0;
> > +}
> > +
> > +static ssize_t i915_dsc_fec_support_write(struct file *file,
> > +					  const char __user *ubuf,
> > +					  size_t len, loff_t *offp)
> > +{
> > +	bool dsc_enable = false;
> > +	int ret;
> > +	struct drm_connector *connector =
> > +		((struct seq_file *)file->private_data)->private;
> > +	struct intel_encoder *encoder = intel_attached_encoder(connector);
> > +	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
> > +
> > +	if (len == 0)
> > +		return 0;
> > +
> > +	DRM_DEBUG_DRIVER("Copied %d bytes from user to force DSC\n",
> > +			 (unsigned int)len);
> You can just use %zu instead of %d here, see:
> 
> https://01.org/linuxgraphics/gfx-docs/drm/core-api/printk-formats.html

Cool I will make this change. Thanks for the review.

Regards
Manasi

> 
> Other then that, looks good to me! With that change:
> 
> Reviewed-by: Lyude Paul <lyude@redhat.com>
> 
> > +
> > +	ret = kstrtobool_from_user(ubuf, len, &dsc_enable);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	DRM_DEBUG_DRIVER("Got %s for DSC Enable\n",
> > +			 (dsc_enable) ? "true" : "false");
> > +	intel_dp->force_dsc_en = dsc_enable;
> > +
> > +	*offp += len;
> > +	return len;
> > +}
> > +
> > +static int i915_dsc_fec_support_open(struct inode *inode,
> > +				     struct file *file)
> > +{
> > +	return single_open(file, i915_dsc_fec_support_show,
> > +			   inode->i_private);
> > +}
> > +
> > +static const struct file_operations i915_dsc_fec_support_fops = {
> > +	.owner = THIS_MODULE,
> > +	.open = i915_dsc_fec_support_open,
> > +	.read = seq_read,
> > +	.llseek = seq_lseek,
> > +	.release = single_release,
> > +	.write = i915_dsc_fec_support_write
> > +};
> > +
> >  /**
> >   * i915_debugfs_connector_add - add i915 specific connector debugfs files
> >   * @connector: pointer to a registered drm_connector
> > @@ -5098,6 +5171,7 @@ DEFINE_SHOW_ATTRIBUTE(i915_hdcp_sink_capability);
> >  int i915_debugfs_connector_add(struct drm_connector *connector)
> >  {
> >  	struct dentry *root = connector->debugfs_entry;
> > +	struct drm_i915_private *dev_priv = to_i915(connector->dev);
> >  
> >  	/* The connector must have been registered beforehands. */
> >  	if (!root)
> > @@ -5122,5 +5196,11 @@ int i915_debugfs_connector_add(struct drm_connector
> > *connector)
> >  				    connector,
> > &i915_hdcp_sink_capability_fops);
> >  	}
> >  
> > +	if (INTEL_GEN(dev_priv) >= 10 &&
> > +	    (connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort ||
> > +	     connector->connector_type == DRM_MODE_CONNECTOR_eDP))
> > +		debugfs_create_file("i915_dsc_fec_support", S_IRUGO, root,
> > +				    connector, &i915_dsc_fec_support_fops);
> > +
> >  	return 0;
> >  }
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > b/drivers/gpu/drm/i915/intel_dp.c
> > index a6907a1761ab..2e3097cae277 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -2051,7 +2051,8 @@ intel_dp_compute_link_config(struct intel_encoder
> > *encoder,
> >  							&limits);
> >  
> >  	/* enable compression if the mode doesn't fit available BW */
> > -	if (!ret) {
> > +	DRM_DEBUG_KMS("Force DSC en = %d\n", intel_dp->force_dsc_en);
> > +	if (!ret || intel_dp->force_dsc_en) {
> >  		if (!intel_dp_dsc_compute_config(intel_dp, pipe_config,
> >  						 conn_state, &limits))
> >  			return false;
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h
> > b/drivers/gpu/drm/i915/intel_drv.h
> > index f94a04b4ad87..0cedce438433 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -1209,6 +1209,9 @@ struct intel_dp {
> >  
> >  	/* Displayport compliance testing */
> >  	struct intel_dp_compliance compliance;
> > +
> > +	/* Display stream compression testing */
> > +	bool force_dsc_en;
> >  };
> >  
> >  enum lspcon_vendor {
> -- 
> Cheers,
> 	Lyude Paul
> 
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