On Wed, 2018-12-05 at 11:29 -0800, Manasi Navare wrote:
> 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@xxxxxxxxx>
> > > Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
> > > Cc: Anusha Srivatsa <anusha.srivatsa@xxxxxxxxx>
> > > Cc: Lyude Paul <lyude@xxxxxxxxxx>
> > > Signed-off-by: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> > > ---
> > > 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..
Mhm, so here's why they are asking for each lock:
connection_mutex: Protects any connector->state, and connector->status.
(As an extra note: ignore connector->mutex for modesetting purposes, only
dev->mode_config.connection_mutex is important.)
crtc->mutex: Anything in crtc->state for the given crtc
In order to avoid to avoid a NULL dereference due to connector->crtc->state
changing, you'd start grabbing locks with something like this:
/* pretend we have 'connector' already set to the drm_connector */
/* also pretend we have 'dev' set to the struct drm_device* */
struct drm_crtc *crtc;
struct drm_modeset_acquire_ctx ctx;
bool try_again = false;
int ret = 0;
drm_modeset_acquire_init(&ctx, 0);
do {
/* We don't check the return code here because since this is
* our first lock, so there isn't any chance of us deadlocking
* yet.
*/
drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
/* Cool! Now that we're holding connection_mutex, we can start
* reading from the connector struct and friends
*/
crtc = connector->state->crtc;
if (connector->status != connector_status_connected || !crtc) {
ret = -ENODEV;
break;
}
/* Now we need to check the return code from
* drm_modeset_lock(), because.......
*/
ret = drm_modeset_lock(&crtc->mutex, &ctx);
if (ret == -EDEADLK) {
/* We could deadlock! If we're here, then this is
* probably what happened:
*
* <CPU1> (us) <CPU2>
* modeset_lock(&conn_mutex); modeset_lock(&crtc->mutex);
* modeset_lock(&crtc->mutex); modeset_lock(&conn_mutex);
*
* CPU1 is waiting for crtc->mutex which is held by CPU2, but
* CPU2 is waiting for conn_mutex, which is held by CPU1
*
* Normally the kernel doesn't run into this issue
* because a lot of care has been put into ordering
* mutex_lock() calls correctly. But, with modesetting
* we don't have the benefit of knowing what order these
* locks will be acquired in. Since drm_modeset_lock()
* has informed us of this scenario however, we can
* avoid hanging the entire kernel by simply dropping
* our locks, in this case that would just include
* connection_mutex. We call this "backing off"
*/
drm_modeset_backoff(&ctx);
/* Now, things will look like this:
*
* <CPU1> (us) <CPU2>
* modeset_lock(&conn_mutex); modeset_lock(&crtc->mutex);
* modeset_lock(&crtc->mutex); modeset_lock(&conn_mutex);
* (oh no, a deadlock!) ...
* modeset_backoff(); (Oh hey, I locked &conn_mutex)
* modeset_lock(&conn_mutex); (now I'm doing stuff, wee!)
* ... modeset_drop_locks();
* (Oh hey, I locked &conn_mutex) ...
* (do stuff) ...
* (etc. etc.)
*/
go_again = true;
continue;
}
/* Now if we're here, we managed to grab both locks correctly,
* and we know neither connector->state or crtc->state will
* change.
*/
intel_dp = enc_to_intel_dp(intel_attached_encoder(connector));
if (intel_dp->dsc_dpcd)
/* etc. etc. */
/* ... */
} while (go_again);
/* Now, we can finally drop any locks we're holding */
drm_modeset_drop_locks(&ctx);
/* And release our acquisition context */
drm_modeset_acquire_fini(&ctx);
return ret;
Does that help explain things?
>
> > > + 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@xxxxxxxxxx>
> >
> > > +
> > > + 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
> >
--
Cheers,
Lyude Paul
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