On Wed, 21 Feb 2024 13:37:10 +0100,
Richard Fitzgerald wrote:
>
> 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@xxxxxxxxxxxxxxxxxxxxx>
> Fixes: 209c6cdfd283 ("ASoC: soc-card: move snd_soc_card_get_kcontrol() to soc-card")
> ---
> It would be great if people could test the fsl/, qcom/, ti/rx51 and ak4418
> drivers.
This fix itself looks correct, and I merged Mark's PR now.
But in general, it'd be better to use snd_ctl_find_id() and
snd_ctl_find_id_unlocked() if possible. Those standard APIs can use
the fast Xarray lookup, and especially for the case like many ASoC
drivers that expose hundreds of kcontrols, the performance gain
becomes significant.
I see that there is no snd_ctl_find_mixer_id_unlocked() variant, but
it should be trivial to add.
thanks,
Takashi
