On Wed, 2021-04-14 at 18:49 +0200, Thierry Reding wrote:
On Fri, Feb 19, 2021 at 04:52:59PM -0500, Lyude Paul wrote:
As pointed out by the documentation for drm_dp_aux_register(), drm_dp_aux_init() should be used in situations where the AUX channel for a display driver can potentially be registered before it's respective DRM driver. This is the case with Tegra, since the DP aux channel exists as a platform device instead of being a grandchild of the DRM device.
Since we're about to add a backpointer to a DP AUX channel's respective DRM device, let's fix this so that we don't potentially allow userspace to use the AUX channel before we've associated it with it's DRM connector.
Signed-off-by: Lyude Paul lyude@redhat.com
drivers/gpu/drm/tegra/dpaux.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/tegra/dpaux.c b/drivers/gpu/drm/tegra/dpaux.c index 105fb9cdbb3b..ea56c6ec25e4 100644 --- a/drivers/gpu/drm/tegra/dpaux.c +++ b/drivers/gpu/drm/tegra/dpaux.c @@ -534,9 +534,7 @@ static int tegra_dpaux_probe(struct platform_device *pdev) dpaux->aux.transfer = tegra_dpaux_transfer; dpaux->aux.dev = &pdev->dev; - err = drm_dp_aux_register(&dpaux->aux); - if (err < 0) - return err; + drm_dp_aux_init(&dpaux->aux);
I just noticed that this change causes an error on some setups that I haven't seen before. The problem is that the SOR driver tries to grab a reference to the I2C device to make sure it doesn't go away while it has a pointer to it.
However, since now the I2C adapter hasn't been registered yet, I get this:
[ 15.013969] kobject: '(null)' (000000005c903e43): is not initialized, yet kobject_get() is being called.
I recall that you wanted to make this change so that a backpointer to the DRM device could be added (I think that's patch 15 of the series), but I didn't see that patch get merged, so it's a bit difficult to try and fix this up.
I'm pretty sure I already merged the tegra change in drm-misc-next, so if it's causing issues you probably should send out a revert for now and I can r-b it so we can figure out a better solution for this in the mean time
Has the situation changed? Do we no longer need the backpointer? If we still want it, what's the plan for merging the change? Should I work under the assumption that patch will make it in sometime and try to fix this on top of that?
yes we do still need the backpointer - I'm just still working on getting reviews for some of the other parts of this series, and have been on PTO/busy with a couple of other things.
I'm thinking that perhaps we can move the I2C adapter registration into drm_dp_aux_init() since that's independent of the DRM device.
Yeah this makes sense for me - I can try to make this change on the next respin of this series. What kind of setup were you able to reproduce issues on this with btw?
It would also make a bit more sense from the Tegra driver's point of view where all devices would be created during the ->probe() path, and only during the ->init() path would the connection between DRM device and DRM DP AUX device be established.
Thierry