[PATCH] ALSA: hda: Do not unset preset when cleaning up codec

[Cezary Rojewski <cezary.rojewski@intel.com>]

Several functions that take part in codec's initialization and removal
are re-used by ASoC codec drivers implementations. Drivers mimic the
behavior of hda_codec_driver_probe/remove() found in
sound/pci/hda/hda_bind.c with their component->probe/remove() instead.

One of the reasons for that is the expectation of
snd_hda_codec_device_new() to receive a valid struct snd_card pointer
what cannot be fulfilled on ASoC side until a card is attempted to be
bound and its component probing is triggered.

As ASoC sound card may be unbound without codec device being actually
removed from the system, unsetting ->preset in 
snd_hda_codec_cleanup_for_unbind() interferes with module unload -> load
scenario causing null-ptr-deref. Preset is assigned only once, during
device/driver matching whereas ASoC codec driver's module reloading may
occur several times throughout the lifetime of an audio stack.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
---

This is a continuation of a discussion that begun in the middle of 2022
[1] and was part of a larger series addressing several HDAudio topics.

Single rmmod on ASoC's codec driver module is enough to cause a panic.
Given our results, no regression shows up with modprobe/rmmod on
snd_hda_intel side with this patch applied.

[1]: https://lore.kernel.org/alsa-devel/20220706120230.427296-2-cezary.rojewski@intel.com/

 sound/pci/hda/hda_codec.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c
index edd653ece70d..ac1cc7c5290e 100644
--- a/sound/pci/hda/hda_codec.c
+++ b/sound/pci/hda/hda_codec.c
@@ -795,7 +795,6 @@ void snd_hda_codec_cleanup_for_unbind(struct hda_codec *codec)
 	snd_array_free(&codec->cvt_setups);
 	snd_array_free(&codec->spdif_out);
 	snd_array_free(&codec->verbs);
-	codec->preset = NULL;
 	codec->follower_dig_outs = NULL;
 	codec->spdif_status_reset = 0;
 	snd_array_free(&codec->mixers);
-- 
2.25.1