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SubjectRe: [RESEND PATCH v2 1/2] drm/dp/mst: Reprobe EDID for MST ports on resume
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Date
Thought this was going to be an easy review until I realized that there's
multiple problems in nouveau this would cause issues with, even if we didn't
pay attention to the -EINVAL that gets returned. The suspend/resume order in
nouveau needs some fixing up to prevent this patch from causing timeouts, and
then also there's a hidden surprise

[ 972.294437] ============================================
[ 972.295225] WARNING: possible recursive locking detected
[ 972.296042] 4.19.0-rc8mst-reprobe+ #2 Not tainted
[ 972.296842] --------------------------------------------
[ 972.297614] zsh/6840 is trying to acquire lock:
[ 972.298441] 0000000072e521f7 (&dev->mode_config.mutex){+.+.}, at:
drm_dp_mst_edids_changed+0xc0/0x180 [drm_kms_helper]
[ 972.299299]
but task is already holding lock:
[ 972.300991] 0000000072e521f7 (&dev->mode_config.mutex){+.+.}, at:
status_store+0x34/0x180 [drm]
[ 972.301875]
other info that might help us debug this:
[ 972.303563] Possible unsafe locking scenario:

[ 972.305315] CPU0
[ 972.306182] ----
[ 972.307061] lock(&dev->mode_config.mutex);
[ 972.307943] lock(&dev->mode_config.mutex);
[ 972.308819]
*** DEADLOCK ***

[ 972.311446] May be due to missing lock nesting notation

[ 972.313234] 6 locks held by zsh/6840:
[ 972.314135] #0: 0000000092b5ba9d (sb_writers#4){.+.+}, at:
vfs_write+0x13e/0x1a0
[ 972.315049] #1: 00000000e628e6e9 (&of->mutex){+.+.}, at:
kernfs_fop_write+0xbd/0x1a0
[ 972.315980] #2: 000000000fb65e6c (kn->count#240){.+.+}, at:
kernfs_fop_write+0xc5/0x1a0
[ 972.316928] #3: 0000000072e521f7 (&dev->mode_config.mutex){+.+.}, at:
status_store+0x34/0x180 [drm]
[ 972.317892] #4: 00000000344224c2 (crtc_ww_class_acquire){+.+.}, at:
drm_helper_probe_single_connector_modes+0x66/0x6c0 [drm_kms_helper]
[ 972.318863] #5: 00000000d65352e2 (crtc_ww_class_mutex){+.+.}, at:
drm_modeset_lock+0x44/0x110 [drm]
[ 972.319860]
stack backtrace:
[ 972.321800] CPU: 5 PID: 6840 Comm: zsh Kdump: loaded Not tainted 4.19.0-
rc8mst-reprobe+ #2
[ 972.322772] Hardware name: LENOVO 20EQZ1J7US/20EQZ1J7US, BIOS N1EET80W
(1.53 ) 09/14/2018
[ 972.323792] Call Trace:
[ 972.324821] dump_stack+0x85/0xc0
[ 972.325832] __lock_acquire.cold.59+0x158/0x227
[ 972.326887] ? retint_kernel+0x10/0x10
[ 972.327918] lock_acquire+0x9e/0x170
[ 972.328948] ? drm_dp_mst_edids_changed+0xc0/0x180 [drm_kms_helper]
[ 972.329986] ? drm_dp_mst_edids_changed+0xc0/0x180 [drm_kms_helper]
[ 972.331066] __mutex_lock+0x68/0x900
[ 972.332094] ? drm_dp_mst_edids_changed+0xc0/0x180 [drm_kms_helper]
[ 972.333146] ? __mutex_unlock_slowpath+0x4b/0x2b0
[ 972.334221] ? drm_dp_mst_edids_changed+0xc0/0x180 [drm_kms_helper]
[ 972.335255] drm_dp_mst_edids_changed+0xc0/0x180 [drm_kms_helper]
[ 972.336318] drm_dp_mst_topology_mgr_resume+0x104/0x190 [drm_kms_helper]
[ 972.337397] nv50_display_init+0x73/0xd0 [nouveau]
[ 972.338483] nouveau_display_init+0x8e/0xe0 [nouveau]
[ 972.339547] nouveau_display_resume+0x39/0x250 [nouveau]
[ 972.340634] ? pci_restore_standard_config+0x40/0x40
[ 972.341762] nouveau_do_resume+0x79/0x150 [nouveau]
[ 972.342850] nouveau_pmops_runtime_resume+0x88/0x150 [nouveau]
[ 972.343915] pci_pm_runtime_resume+0x78/0xb0
[ 972.345004] __rpm_callback+0x75/0x1b0
[ 972.346084] ? pci_restore_standard_config+0x40/0x40
[ 972.347148] rpm_callback+0x1f/0x70
[ 972.348256] ? pci_restore_standard_config+0x40/0x40
[ 972.349351] rpm_resume+0x5d4/0x810
[ 972.350446] ? drm_modeset_lock+0x44/0x110 [drm]
[ 972.351573] __pm_runtime_resume+0x47/0x70
[ 972.352737] nouveau_connector_detect+0x373/0x470 [nouveau]
[ 972.353841] ? _cond_resched+0x15/0x30
[ 972.354945] ? ww_mutex_lock+0x30/0x60
[ 972.356044] ? drm_modeset_lock+0x44/0x110 [drm]
[ 972.357146] drm_helper_probe_single_connector_modes+0xd9/0x6c0
[drm_kms_helper]
[ 972.358274] ? printk+0x58/0x6f
[ 972.359400] status_store+0xb2/0x180 [drm]
[ 972.360519] kernfs_fop_write+0xf0/0x1a0
[ 972.361711] __vfs_write+0x36/0x180
[ 972.362842] ? rcu_read_lock_sched_held+0x55/0x60
[ 972.363974] ? rcu_sync_lockdep_assert+0x2e/0x60
[ 972.365103] ? __sb_start_write+0x115/0x170
[ 972.366241] ? vfs_write+0x13e/0x1a0
[ 972.367365] vfs_write+0xa5/0x1a0
[ 972.368486] ksys_write+0x52/0xc0
[ 972.369596] do_syscall_64+0x60/0x1a0
[ 972.370782] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 972.371890] RIP: 0033:0x7fc93e169ef4
[ 972.373012] Code: 89 02 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00
00 66 90 48 8d 05 f1 3a 2d 00 8b 00 85 c0 75 13 b8 01 00 00 00 0f 05 <48> 3d
00 f0 ff ff 77 54 c3 0f 1f 00 41 54 49 89 d4 55 48 89 f5 53
[ 972.374214] RSP: 002b:00007ffcd7ad1918 EFLAGS: 00000246 ORIG_RAX:
0000000000000001
[ 972.375421] RAX: ffffffffffffffda RBX: 0000000000000007 RCX:
00007fc93e169ef4
[ 972.376628] RDX: 0000000000000007 RSI: 000055aefe5c30c0 RDI:
0000000000000001
[ 972.377872] RBP: 000055aefe5c30c0 R08: 00007fc93e43a8c0 R09:
00007fc93f6cdb80
[ 972.379082] R10: 000000000000000a R11: 0000000000000246 R12:
00007fc93e439760
[ 972.380311] R13: 0000000000000007 R14: 00007fc93e434760 R15:
0000000000000007

I must not have noticed that back when I wrote these patches! Whoops.

Since there's going to be quite a number of changes I need to make to this I'm
just going to make the changes myself! I'll make sure to Cc you with the
respin

On Tue, 2018-10-23 at 19:19 -0700, Juston Li wrote:
> From: Lyude <cpaul@redhat.com>
>
> As observed with the latest ThinkPad docks, we unfortunately can't rely
> on docks keeping us updated with hotplug events that happened while we
> were suspended. On top of that, even if the number of connectors remains
> the same between suspend and resume it's still not safe to assume that
> there were no hotplugs, since a different monitor might have been
> plugged into a port another monitor previously occupied. As such, we
> need to go through all of the MST ports and check whether or not their
> EDIDs have changed.
>
> In addition to that, we also now return -EINVAL from
> drm_dp_mst_topology_mgr_resume to indicate to callers that they need to
> reset the MST connection, and that they can't rely on any other method
> of reprobing.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Lyude <cpaul@redhat.com>
> Signed-off-by: Juston Li <juston.li@intel.com>
> ---
> drivers/gpu/drm/drm_dp_mst_topology.c | 94 ++++++++++++++++++++++++++-
> 1 file changed, 93 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 5ff1d79b86c4..88abebe52021 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -29,6 +29,7 @@
> #include <linux/i2c.h>
> #include <drm/drm_dp_mst_helper.h>
> #include <drm/drmP.h>
> +#include <drm/drm_edid.h>
>
> #include <drm/drm_fixed.h>
> #include <drm/drm_atomic.h>
> @@ -2201,6 +2202,64 @@ void drm_dp_mst_topology_mgr_suspend(struct
> drm_dp_mst_topology_mgr *mgr)
> }
> EXPORT_SYMBOL(drm_dp_mst_topology_mgr_suspend);
>
> +static bool drm_dp_mst_edids_changed(struct drm_dp_mst_topology_mgr *mgr,
> + struct drm_dp_mst_port *port)
> +{
> + struct drm_device *dev;
> + struct drm_connector *connector;
> + struct drm_dp_mst_port *dport;
> + struct drm_dp_mst_branch *mstb;
> + struct edid *current_edid, *cached_edid;
> + bool ret = false;
> +
> + port = drm_dp_get_validated_port_ref(mgr, port);
> + if (!port)
> + return false;
> +
> + mstb = drm_dp_get_validated_mstb_ref(mgr, port->mstb);
> + if (mstb) {
> + list_for_each_entry(dport, &port->mstb->ports, next) {
> + ret = drm_dp_mst_edids_changed(mgr, dport);
> + if (ret)
> + break;
> + }
> +
> + drm_dp_put_mst_branch_device(mstb);
> + if (ret)
> + goto out;
> + }
> +
> + connector = port->connector;
> + if (!connector || !port->aux.ddc.algo)
> + goto out;
> +
> + dev = connector->dev;
> + mutex_lock(&dev->mode_config.mutex);
> +
> + current_edid = drm_get_edid(connector, &port->aux.ddc);
> + if (connector->edid_blob_ptr)
> + cached_edid = (void *)connector->edid_blob_ptr->data;
> + else
> + return false;
> +
> + if ((current_edid && cached_edid && memcmp(current_edid, cached_edid,
> + sizeof(struct edid)) != 0)
> ||
> + (!current_edid && cached_edid) || (current_edid && !cached_edid))
> {
> + ret = true;
> + DRM_DEBUG_KMS("EDID on %s changed, reprobing connectors\n",
> + connector->name);
> + }
> +
> + mutex_unlock(&dev->mode_config.mutex);
> +
> + kfree(current_edid);
> +
> +out:
> + drm_dp_put_port(port);
> +
> + return ret;
> +}
> +
> /**
> * drm_dp_mst_topology_mgr_resume() - resume the MST manager
> * @mgr: manager to resume
> @@ -2210,9 +2269,15 @@ EXPORT_SYMBOL(drm_dp_mst_topology_mgr_suspend);
> *
> * if the device fails this returns -1, and the driver should do
> * a full MST reprobe, in case we were undocked.
> + *
> + * if the device can no longer be trusted, this returns -EINVAL
> + * and the driver should unconditionally disconnect and reconnect
> + * the dock.
> */
> int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr)
> {
> + struct drm_dp_mst_branch *mstb;
> + struct drm_dp_mst_port *port;
> int ret = 0;
>
> mutex_lock(&mgr->lock);
> @@ -2246,8 +2311,35 @@ int drm_dp_mst_topology_mgr_resume(struct
> drm_dp_mst_topology_mgr *mgr)
> drm_dp_check_mstb_guid(mgr->mst_primary, guid);
>
> ret = 0;
> - } else
> +
> + /*
> + * Some hubs also forget to notify us of hotplugs that
> happened
> + * while we were in suspend, so we need to verify that the
> edid
> + * hasn't changed for any of the connectors. If it has been,
> + * we unfortunately can't rely on the dock updating us with
> + * hotplug events, so indicate we need a full reconnect.
> + */
> +
> + /* MST's I2C helpers can't be used while holding this lock */
> + mutex_unlock(&mgr->lock);
> +
> + mstb = drm_dp_get_validated_mstb_ref(mgr, mgr->mst_primary);
> + if (mstb) {
> + list_for_each_entry(port, &mstb->ports, next) {
> + if (drm_dp_mst_edids_changed(mgr, port)) {
> + ret = -EINVAL;
> + break;
> + }
> + }
> +
> + drm_dp_put_mst_branch_device(mstb);
> + }
> + } else {
> ret = -1;
> + mutex_unlock(&mgr->lock);
> + }
> +
> + return ret;
>
> out_unlock:
> mutex_unlock(&mgr->lock);
--
Cheers,
Lyude Paul

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