soundwire: cadence: add parity error injection through debugfs

The Cadence IP can inject errors, let's make use of this capability to
test Slave parity error checks.

See e.g. example log where both the master and slave detect the parity
error injected on a dummy read command.

cd /sys/kernel/debug/soundwire/master-1/intel-sdw/
echo 1 > cdns-parity-error-injection

[ 44.756249] intel-master sdw-master-1: Parity error
[ 44.756313] intel-master sdw-master-1: Msg NACK received
[ 44.756366] intel-master sdw-master-1: Msg NACKed for Slave 15
[ 44.756375] intel-master sdw-master-1: trf on Slave 15 failed:-5
[ 44.756382] intel-master sdw-master-1: parity error injection, read: -5
[ 44.756649] rt1308 sdw:1:25d:1308:0: Parity error detected

The code makes sure the Master device is resumed, hence the clock
restarted, before sending a parity error.

Signed-off-by: Pierre-Louis Bossart <[e-mail]>
Signed-off-by: Bard Liao <[e-mail]>
Reviewed-by: Kai Vehmanen <[e-mail]>
Reviewed-by: Guennadi Liakhovetski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/soundwire/cadence_master.c

···
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/mod_devicetable.h>
+#include <linux/pm_runtime.h>
 #include <linux/soundwire/sdw_registers.h>
 #include <linux/soundwire/sdw.h>
 #include <sound/pcm_params.h>
···
 #define CDNS_MCP_CONTROL_BLOCK_WAKEUP		BIT(0)
 
 #define CDNS_MCP_CMDCTRL			0x8
+
+#define CDNS_MCP_CMDCTRL_INSERT_PARITY_ERR	BIT(2)
+
 #define CDNS_MCP_SSPSTAT			0xC
 #define CDNS_MCP_FRAME_SHAPE			0x10
 #define CDNS_MCP_FRAME_SHAPE_INIT		0x14
···
 
 DEFINE_DEBUGFS_ATTRIBUTE(cdns_hw_reset_fops, NULL, cdns_hw_reset, "%llu\n");
 
+static int cdns_parity_error_injection(void *data, u64 value)
+{
+	struct sdw_cdns *cdns = data;
+	struct sdw_bus *bus;
+	int ret;
+
+	if (value != 1)
+		return -EINVAL;
+
+	bus = &cdns->bus;
+
+	/*
+	 * Resume Master device. If this results in a bus reset, the
+	 * Slave devices will re-attach and be re-enumerated.
+	 */
+	ret = pm_runtime_get_sync(bus->dev);
+	if (ret < 0 && ret != -EACCES) {
+		dev_err_ratelimited(cdns->dev,
+				    "pm_runtime_get_sync failed in %s, ret %d\n",
+				    __func__, ret);
+		pm_runtime_put_noidle(bus->dev);
+		return ret;
+	}
+
+	/*
+	 * wait long enough for Slave(s) to be in steady state. This
+	 * does not need to be super precise.
+	 */
+	msleep(200);
+
+	/*
+	 * Take the bus lock here to make sure that any bus transactions
+	 * will be queued while we inject a parity error on a dummy read
+	 */
+	mutex_lock(&bus->bus_lock);
+
+	/* program hardware to inject parity error */
+	cdns_updatel(cdns, CDNS_MCP_CMDCTRL,
+		     CDNS_MCP_CMDCTRL_INSERT_PARITY_ERR,
+		     CDNS_MCP_CMDCTRL_INSERT_PARITY_ERR);
+
+	/* commit changes */
+	cdns_updatel(cdns, CDNS_MCP_CONFIG_UPDATE,
+		     CDNS_MCP_CONFIG_UPDATE_BIT,
+		     CDNS_MCP_CONFIG_UPDATE_BIT);
+
+	/* do a broadcast dummy read to avoid bus clashes */
+	ret = sdw_bread_no_pm_unlocked(&cdns->bus, 0xf, SDW_SCP_DEVID_0);
+	dev_info(cdns->dev, "parity error injection, read: %d\n", ret);
+
+	/* program hardware to disable parity error */
+	cdns_updatel(cdns, CDNS_MCP_CMDCTRL,
+		     CDNS_MCP_CMDCTRL_INSERT_PARITY_ERR,
+		     0);
+
+	/* commit changes */
+	cdns_updatel(cdns, CDNS_MCP_CONFIG_UPDATE,
+		     CDNS_MCP_CONFIG_UPDATE_BIT,
+		     CDNS_MCP_CONFIG_UPDATE_BIT);
+
+	/* Continue bus operation with parity error injection disabled */
+	mutex_unlock(&bus->bus_lock);
+
+	/* Userspace changed the hardware state behind the kernel's back */
+	add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+
+	/*
+	 * allow Master device to enter pm_runtime suspend. This may
+	 * also result in Slave devices suspending.
+	 */
+	pm_runtime_mark_last_busy(bus->dev);
+	pm_runtime_put_autosuspend(bus->dev);
+
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(cdns_parity_error_fops, NULL,
+			 cdns_parity_error_injection, "%llu\n");
+
 /**
  * sdw_cdns_debugfs_init() - Cadence debugfs init
  * @cdns: Cadence instance
···
 
 	debugfs_create_file("cdns-hw-reset", 0200, root, cdns,
 			    &cdns_hw_reset_fops);
+
+	debugfs_create_file("cdns-parity-error-injection", 0200, root, cdns,
+			    &cdns_parity_error_fops);
 }
 EXPORT_SYMBOL_GPL(sdw_cdns_debugfs_init);