ASoC: ti: davinci-mcasp: Fix race condition during probe

When using davinci-mcasp as CPU DAI with simple-card, there are some
conditions that cause simple-card to finish registering a sound card before
davinci-mcasp finishes registering all sound components. This creates a
non-working sound card from userspace with no problem indication apart
from not being able to play/record audio on a PCM stream. The issue
arises during simultaneous probe execution of both drivers. Specifically,
the simple-card driver, awaiting a CPU DAI, proceeds as soon as
davinci-mcasp registers its DAI. However, this process can lead to the
client mutex lock (client_mutex in soc-core.c) being held or davinci-mcasp
being preempted before PCM DMA registration on davinci-mcasp finishes.
This situation occurs when the probes of both drivers run concurrently.
Below is the code path for this condition. To solve the issue, defer
davinci-mcasp CPU DAI registration to the last step in the audio part of
it. This way, simple-card CPU DAI parsing will be deferred until all
audio components are registered.

Fail Code Path:

simple-card.c: probe starts
simple-card.c: simple_dai_link_of: simple_parse_node(..,cpu,..) returns EPROBE_DEFER, no CPU DAI yet
davinci-mcasp.c: probe starts
davinci-mcasp.c: devm_snd_soc_register_component() register CPU DAI
simple-card.c: probes again, finish CPU DAI parsing and call devm_snd_soc_register_card()
simple-card.c: finish probe
davinci-mcasp.c: *dma_pcm_platform_register() register PCM  DMA
davinci-mcasp.c: probe finish

Cc: [email protected]
Fixes: 9fbd58c ("ASoC: davinci-mcasp: Choose PCM driver based on configured DMA controller")
Signed-off-by: Joao Paulo Goncalves <[email protected]>
Acked-by: Peter Ujfalusi <[email protected]>
Reviewed-by: Jai Luthra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mark Brown <[email protected]>

Author: JPSGoncalves

sound/soc/ti/davinci-mcasp.c

@@ -2417,12 +2417,6 @@ static int davinci_mcasp_probe(struct platform_device *pdev)
 
 	mcasp_reparent_fck(pdev);
 
-	ret = devm_snd_soc_register_component(&pdev->dev, &davinci_mcasp_component,
-					      &davinci_mcasp_dai[mcasp->op_mode], 1);
-
-	if (ret != 0)
-		goto err;
-
 	ret = davinci_mcasp_get_dma_type(mcasp);
 	switch (ret) {
 	case PCM_EDMA:
@@ -2449,6 +2443,12 @@ static int davinci_mcasp_probe(struct platform_device *pdev)
 		goto err;
 	}
 
+	ret = devm_snd_soc_register_component(&pdev->dev, &davinci_mcasp_component,
+					      &davinci_mcasp_dai[mcasp->op_mode], 1);
+
+	if (ret != 0)
+		goto err;
+
 no_audio:
 	ret = davinci_mcasp_init_gpiochip(mcasp);
 	if (ret) {