Hi,
On Mon, Sep 30, 2024 at 03:45:13PM -0400, Lyude Paul wrote:
On Mon, 2024-09-30 at 09:06 +0200, Thomas Zimmermann wrote:
Hi
Am 30.09.24 um 09:01 schrieb Maxime Ripard:
Hi,
On Fri, Sep 27, 2024 at 04:46:16PM GMT, Lyude Paul wrote:
Something I discovered while writing rvkms since some versions of the driver didn't have a filled out atomic_update function - we mention that this callback is "optional", but we don't actually check whether it's NULL or not before calling it. As a result, we'll segfault if it's not filled in.
rvkms rvkms.0: [drm:drm_atomic_helper_commit_modeset_disables] modeset on [ENCODER:36:Virtual-36] BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0010 [#1] PREEMPT SMP NOPTI Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240813-1.fc40 08/13/2024 RIP: 0010:0x0
So, let's fix that.
Signed-off-by: Lyude Paul lyude@redhat.com Fixes: c2fcd274bce5 ("drm: Add atomic/plane helpers") Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v3.19+
So we had kind of a similar argument with drm_connector_init early this year, but I do agree we shouldn't fault if we're missing a callback.
I do wonder how we can implement a plane without atomic_update though? Do we have drivers in such a case?
That would likely be an output with an entirely static display. Hard to imaging, I think.
If not, a better solution would be to make it mandatory and check it when registering.
Although I r-b'ed the patch already, I'd also prefer this solution.
Gotcha, FWIW the reason I went with this patch:
- atomic_update is actually documented as being optional in the kernel docs, so we'd want to remove that if we make it mandatory
Sure, that makes total sense :)
- rvkms currently doesn't have an atomic_update. We will likely have one whenever I get a chance to actually add CRC and/or writeback connector supports - but for the time being all we do is register a KMS device with vblank support.
WIP drivers can provide an empty implementation. And even if actually didn't need it for $REASONS, I'd argue that an empty implementation (and a comment) makes that explicit instead of making the reader guess why it's not needed.
Maxime