ASoC: soc-card: Fix missing locking in snd_soc_card_get_kcontrol()

ASoC: soc-card: Fix missing locking in snd_soc_card_get_kcontrol()

snd_soc_card_get_kcontrol() must be holding a read lock on
card->controls_rwsem while walking the controls list.

Compare with snd_ctl_find_numid().

The existing function is renamed snd_soc_card_get_kcontrol_locked()
so that it can be called from contexts that are already holding
card->controls_rwsem (for example, control get/put functions).

There are few direct or indirect callers of
snd_soc_card_get_kcontrol(), and most are safe. Three require
changes, which have been included in this patch:

codecs/cs35l45.c:
  cs35l45_activate_ctl() is called from a control put() function so
  is changed to call snd_soc_card_get_kcontrol_locked().

codecs/cs35l56.c:
  cs35l56_sync_asp1_mixer_widgets_with_firmware() is called from
  control get()/put() functions so is changed to call
  snd_soc_card_get_kcontrol_locked().

fsl/fsl_xcvr.c:
  fsl_xcvr_activate_ctl() is called from three places, one of which
  already holds card->controls_rwsem:
  1. fsl_xcvr_mode_put(), a control put function, which will
     already be holding card->controls_rwsem.
  2. fsl_xcvr_startup(), a DAI startup function.
  3. fsl_xcvr_shutdown(), a DAI shutdown function.

  To fix this, fsl_xcvr_activate_ctl() has been changed to call
  snd_soc_card_get_kcontrol_locked() so that it is safe to call
  directly from fsl_xcvr_mode_put().
  The fsl_xcvr_startup() and fsl_xcvr_shutdown() functions have been
  changed to take a read lock on card->controls_rsem() around calls
  to fsl_xcvr_activate_ctl(). While this is not very elegant, it
  keeps the change small, to avoid this patch creating a large
  collateral churn in fsl/fsl_xcvr.c.

Analysis of other callers of snd_soc_card_get_kcontrol() is that
they do not need any changes, they are not holding card->controls_rwsem
when they call snd_soc_card_get_kcontrol().

Direct callers of snd_soc_card_get_kcontrol():
  fsl/fsl_spdif.c: fsl_spdif_dai_probe() - DAI probe function
  fsl/fsl_micfil.c: voice_detected_fn() - IRQ handler

Indirect callers via soc_component_notify_control():
  codecs/cs42l43: cs42l43_mic_shutter() - IRQ handler
  codecs/cs42l43: cs42l43_spk_shutter() - IRQ handler
  codecs/ak4118.c: ak4118_irq_handler() - IRQ handler
  codecs/wm_adsp.c: wm_adsp_write_ctl() - not currently used

Indirect callers via snd_soc_limit_volume():
  qcom/sc8280xp.c: sc8280xp_snd_init() - DAIlink init function
  ti/rx51.c: rx51_aic34_init() - DAI init function

I don't have hardware to test the fsl/*, qcom/sc828xp.c, ti/rx51.c
and ak4118.c changes.

Backport note:
The fsl/, qcom/, cs35l45, cs35l56 and cs42l43 callers were added
since the Fixes commit so won't all be present on older kernels.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: 209c6cdfd283 ("ASoC: soc-card: move snd_soc_card_get_kcontrol() to soc-card")
Link: https://lore.kernel.org/r/20240221123710.690224-1-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>