ASoC: SOF: core: remove DSP after unregistering machine driver

snd_sof_remove() disables the DSP and unmaps the DSP BAR.
Removing topology after disabling the DSP results in a
kernel panic while unloading the pipeline widget. This is
because pipeline widget unload attempts to power down
the core it is scheduled on by accessing the DSP registers.

So, the suggested fix here is to unregister the machine driver
first to remove the topology and then disable the DSP
to avoid the situation described above.

Note that the kernel panic only happens in cases where the
HDaudio link is not managed by the hdac library,
e.g. no codec or when HDMI is not supported.
When the hdac library is used, snd_sof_remove() calls
snd_hdac_ext_bus_device_remove() to remove the codec which
unregisters the component driver thereby also removing the
topology before the DSP is disabled.

Fixes: c16211d6 ("ASoC: SOF: Add Sound Open Firmware driver core")
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/core.c

@@ -484,7 +484,6 @@ int snd_sof_device_remove(struct device *dev)
 	snd_sof_ipc_free(sdev);
 	snd_sof_free_debug(sdev);
 	snd_sof_free_trace(sdev);
-	snd_sof_remove(sdev);
 
 	/*
 	 * Unregister machine driver. This will unbind the snd_card which
@@ -494,6 +493,14 @@ int snd_sof_device_remove(struct device *dev)
 	if (!IS_ERR_OR_NULL(pdata->pdev_mach))
 		platform_device_unregister(pdata->pdev_mach);
 
+	/*
+	 * Unregistering the machine driver results in unloading the topology.
+	 * Some widgets, ex: scheduler, attempt to power down the core they are
+	 * scheduled on, when they are unloaded. Therefore, the DSP must be
+	 * removed only after the topology has been unloaded.
+	 */
+	snd_sof_remove(sdev);
+
 	/* release firmware */
 	release_firmware(pdata->fw);
 	pdata->fw = NULL;