[0/7] media: Fix mishandling of MEDIA_PAD_FL_MUST_CONNECT flag

Hello,

This patch series fixes mishandling of the MEDIA_PAD_FL_MUST_CONNECT
flag.

The issue has been introduced in commit ae219872834a ("media: mc:
entity: Rewrite media_pipeline_start()") when reworking the media
controller pipeline validation code. It is known to cause crashes in the
imx-mipi-csis driver (see [1]) and most likely affects multiple other
drivers. Patch 1/7 and 2/7 fix the problem.

Patches 3/7 to 7/7 fix an additional related issue affecting the
imx8-isi driver. It is however not a regression introduced by commit
ae219872834a. The problem causes a NULL pointer dereference when
enabling streams if the pipeline is configured with the imx8-isi
crossbar sink pad not being connected. Patch 3/7, initially submitted by
Marek, fixes the issue in the imx8-isi driver itself.

As the problem is very similar to what the MUST_CONNECT flag was
designed to handled, I considered the bug to be better solved by using
the MUST_CONNECT flag in the imx8-isi driver. This requires expanding
the purpose of the flag (patch 6/7), after a few drive-by fixes and
reworks (patches 4/7 and 5/7). Finally, patch 7/7 sets the MUST_CONNECT
flag in the imx8-isi driver, effectively reverting the changes from
patch 3/7.

I have decided to still include patch 3/7 in the series, as in the even
that the changes in patches 4/7 to 7/7 were to be reverted later (or
simply require more discussions and new versions), patches 1/7 to 3/7
could be merged without delay and fix the issue for users.

[1] https://lore.kernel.org/linux-media/7658a15a-80c5-219f-2477-2a94ba6c6ba1@kontron.de

Laurent Pinchart (6):
  media: mc: Add local pad to pipeline regardless of the link state
  media: mc: Fix flags handling when creating pad links
  media: mc: Add num_links flag to media_pad
  media: mc: Rename pad variable to clarify intent
  media: mc: Expand MUST_CONNECT flag to always require an enabled link
  media: nxp: imx8-isi: Mark all crossbar sink pads as MUST_CONNECT

Marek Vasut (1):
  media: nxp: imx8-isi: Check whether crossbar pad is non-NULL before
    access

 .../media/mediactl/media-types.rst            | 11 +--
 drivers/media/mc/mc-entity.c                  | 93 ++++++++++++++-----
 .../platform/nxp/imx8-isi/imx8-isi-crossbar.c |  4 +-
 include/media/media-entity.h                  |  2 +
 4 files changed, 78 insertions(+), 32 deletions(-)


base-commit: 0dd3ee31125508cd67f7e7172247f05b7fd1753a