Re: drm: DP update that fixes T460 external monitors through docks

[Paul Irofti]

On Fri, Jan 26, 2018 at 10:39:39AM +0200, Paul Irofti wrote:
> Hi,
> 
> I have a T460 Lenovo model that, when connected to an external monitor
> via a docking station, freezes the machine and produces the "snowflake"
> effect on the monitor. Last time I saw this was in 2010 when working on
> suspend-resume :)
> 
> After a month of fighting to fix the issue I came up with this drm
> update. The code bellow includes commits taken directly from the Linux
> kernel, no local modifications.
> 
> Notable changes are:
>       - improved DP link training by renegotiating with different rates and
>         lane values
>       - caching of source, sink and common rates
>       - max link rate limiting and related calculation changes
>       - switch to long and short pulse interrupts
> 
> I have been running succesfully with this on both the affected model and
> on the x250 that I used with a dozen monitors, projectors and the like
> at uni. No problems so far, but would appreciate test repaorts on a
> wider range of hardware.
> 
> Comments? Mistakes? How should we proceed to get this in the tree?

For the archives, here is a diff that fixes a locking warning with the
earlier patch. So you have to apply it after the former one.

diff --git sys/dev/pci/drm/drm_probe_helper.c sys/dev/pci/drm/drm_probe_helper.c
index 936c0c1d3a7..84a0e585d32 100644
--- sys/dev/pci/drm/drm_probe_helper.c
+++ sys/dev/pci/drm/drm_probe_helper.c
@@ -136,15 +136,27 @@ static int 
drm_helper_probe_single_connector_modes_merge_bits(struct drm_connect
        struct drm_display_mode *mode;
        const struct drm_connector_helper_funcs *connector_funcs =
                connector->helper_private;
-       int count = 0;
+       int count = 0, ret;
        int mode_flags = 0;
        bool verbose_prune = true;
        enum drm_connector_status old_status;
+       struct drm_modeset_acquire_ctx ctx;
 
        WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
 
        DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
                        connector->name);
+
+       drm_modeset_acquire_init(&ctx, 0);
+
+retry:
+       ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
+       if (ret == -EDEADLK) {
+               drm_modeset_backoff(&ctx);
+               goto retry;
+       } else
+               WARN_ON(ret < 0);
+
        /* set all modes to the unverified state */
        list_for_each_entry(mode, &connector->modes, head)
                mode->status = MODE_UNVERIFIED;
@@ -248,6 +260,9 @@ static int 
drm_helper_probe_single_connector_modes_merge_bits(struct drm_connect
 prune:
        drm_mode_prune_invalid(dev, &connector->modes, verbose_prune);
 
+       drm_modeset_drop_locks(&ctx);
+       drm_modeset_acquire_fini(&ctx);
+
        if (list_empty(&connector->modes))
                return 0;