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Date:   Fri, 1 Dec 2017 17:52:03 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Vinod Koul <vinod.koul@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        ALSA <alsa-devel@...a-project.org>, Mark <broonie@...nel.org>,
        Takashi <tiwai@...e.de>, patches.audio@...el.com,
        alan@...ux.intel.com,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Sagar Dharia <sdharia@...eaurora.org>,
        srinivas.kandagatla@...aro.org, plai@...eaurora.org,
        Sudheer Papothi <spapothi@...eaurora.org>
Subject: Re: [alsa-devel] [PATCH v4 09/15] soundwire: Add slave status
 handling

On 12/1/17 3:56 AM, Vinod Koul wrote:
> Add status handling API sdw_handle_slave_status() to handle
> Slave status changes.
> 
> Signed-off-by: Hardik T Shah <hardik.t.shah@...el.com>
> Signed-off-by: Sanyog Kale <sanyog.r.kale@...el.com>
> Signed-off-by: Vinod Koul <vinod.koul@...el.com>
> ---
>   drivers/soundwire/bus.c       | 351 ++++++++++++++++++++++++++++++++++++++++++
>   drivers/soundwire/bus.h       |   2 +
>   include/linux/soundwire/sdw.h |  20 +++
>   3 files changed, 373 insertions(+)
> 
> diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
> index 09126ddd3cdd..c6a59a7a1306 100644
> --- a/drivers/soundwire/bus.c
> +++ b/drivers/soundwire/bus.c
> @@ -602,3 +602,354 @@ static int sdw_initialize_slave(struct sdw_slave *slave)
>   
>   	return 0;
>   }
> +
> +static int sdw_handle_dp0_interrupt(struct sdw_slave *slave, u8 *slave_status)
> +{
> +	u8 clear = 0, impl_int_mask;
> +	int status, ret, count = 0;
> +
> +	status = sdw_read(slave, SDW_DP0_INT);
> +	if (status < 0) {
> +		dev_err(slave->bus->dev,
> +				"SDW_DP0_INT read failed:%d", status);
> +		return status;
> +	}
> +
> +	do {
> +
> +		if (status & SDW_DP0_INT_TEST_FAIL) {
> +			dev_err(&slave->dev, "Test fail for port 0");
> +			clear |= SDW_DP0_INT_TEST_FAIL;
> +		}
> +
> +		/*
> +		 * Assumption: PORT_READY interrupt will be received only for
> +		 * ports implementing Channel Prepare state machine (CP_SM)
> +		 */
> +
> +		if (status & SDW_DP0_INT_PORT_READY) {
> +			complete(&slave->port_ready[0]);
> +			clear |= SDW_DP0_INT_PORT_READY;
> +		}
> +
> +		if (status & SDW_DP0_INT_BRA_FAILURE) {
> +			dev_err(&slave->dev, "BRA failed");
> +			clear |= SDW_DP0_INT_BRA_FAILURE;
> +		}
> +
> +		impl_int_mask = SDW_DP0_INT_IMPDEF1 |
> +			SDW_DP0_INT_IMPDEF2 | SDW_DP0_INT_IMPDEF3;
> +
> +		if (status & impl_int_mask) {
> +			clear |= impl_int_mask;
> +			*slave_status = clear;
> +		}
> +
> +		/* clear the interrupt */
> +		ret = sdw_write(slave, SDW_DP0_INT, clear);
> +		if (ret < 0) {
> +			dev_err(slave->bus->dev,
> +				"SDW_DP0_INT write failed:%d", ret);
> +			return ret;
> +		}
> +
> +		/* Read DP0 interrupt again */
> +		status = sdw_read(slave, SDW_DP0_INT);
> +		if (status < 0) {
> +			dev_err(slave->bus->dev,
> +				"SDW_DP0_INT read failed:%d", status);
> +			return status;
> +		}
> +
> +		count++;
> +
> +		/* we can get alerts while processing so keep retrying */

This is not incorrect, but this goes beyond what the spec requires.

The additional read is to make sure some interrupts are not lost due to 
a known race condition. It would be enough to mask the status read the 
second time to only check if the interrupts sources which were cleared 
are still signaling something.

With the code as it is, you may catch *new* interrupt sources, which 
could impact the arbitration/priority/policy in handling interrupts. 
It's not necessarily bad, but you'd need to document whether you want to 
deal with the race condition described in the MIPI spec or try to be 
smarter.


> +	} while (status != 0 && count < SDW_READ_INTR_CLEAR_RETRY);
> +
> +	if (count == SDW_READ_INTR_CLEAR_RETRY)
> +		dev_warn(slave->bus->dev, "Reached MAX_RETRY on DP0 read");
> +
> +	return ret;
> +}
> +
> +static int sdw_handle_port_interrupt(struct sdw_slave *slave,
> +		int port, u8 *slave_status)
> +{
> +	u8 clear = 0, impl_int_mask;
> +	int status, ret, count = 0;
> +	u32 addr;
> +
> +	if (port == 0)
> +		return sdw_handle_dp0_interrupt(slave, slave_status);
> +
> +	addr = SDW_DPN_INT(port);
> +	status = sdw_read(slave, addr);
> +	if (status < 0) {
> +		dev_err(slave->bus->dev,
> +				"SDW_DPN_INT read failed:%d", status);
> +
> +		return status;
> +	}
> +
> +	do {
> +
> +		if (status & SDW_DPN_INT_TEST_FAIL) {
> +			dev_err(&slave->dev, "Test fail for port:%d", port);
> +			clear |= SDW_DPN_INT_TEST_FAIL;
> +		}
> +
> +		/*
> +		 * Assumption: PORT_READY interrupt will be received only
> +		 * for ports implementing CP_SM.
> +		 */
> +		if (status & SDW_DPN_INT_PORT_READY) {
> +			complete(&slave->port_ready[port]);
> +			clear |= SDW_DPN_INT_PORT_READY;
> +		}
> +
> +		impl_int_mask = SDW_DPN_INT_IMPDEF1 |
> +			SDW_DPN_INT_IMPDEF2 | SDW_DPN_INT_IMPDEF3;
> +
> +
> +		if (status & impl_int_mask) {
> +			clear |= impl_int_mask;
> +			*slave_status = clear;
> +		}
> +
> +		/* clear the interrupt */
> +		ret = sdw_write(slave, addr, clear);
> +		if (ret < 0) {
> +			dev_err(slave->bus->dev,
> +					"SDW_DPN_INT write failed:%d", ret);
> +			return ret;
> +		}
> +
> +		/* Read DPN interrupt again */
> +		status = sdw_read(slave, addr);
> +		if (status < 0) {
> +			dev_err(slave->bus->dev,
> +					"SDW_DPN_INT read failed:%d", status);
> +			return status;
> +		}
> +
> +		count++;
> +
> +		/* we can get alerts while processing so keep retrying */
> +	} while (status != 0 && count < SDW_READ_INTR_CLEAR_RETRY);
> +
> +	if (count == SDW_READ_INTR_CLEAR_RETRY)
> +		dev_warn(slave->bus->dev, "Reached MAX_RETRY on port read");
> +
> +	return ret;
> +}
> +
> +static int sdw_handle_slave_alerts(struct sdw_slave *slave)
> +{
> +	u8 clear = 0, bit, port_status[15];
> +	int port_num, stat, ret, count = 0;
> +	unsigned long port;
> +	bool slave_notify = false;
> +	u8 buf[3];
> +
> +	sdw_modify_slave_status(slave, SDW_SLAVE_ALERT);
> +
> +	/* Read Instat 1, Instat 2 and Instat 3 registers */
> +	ret = sdw_nread(slave, SDW_SCP_INT1, 3, buf);
> +	if (ret < 0) {
> +		dev_err(slave->bus->dev,
> +					"SDW_SCP_INT1 read failed:%d", ret);
> +		return ret;
> +	}
> +
> +	do {
> +		/*
> +		 * Check parity, bus clash and Slave (impl defined)
> +		 * interrupt
> +		 */
> +		if (buf[0] & SDW_SCP_INT1_PARITY) {
> +			dev_err(&slave->dev, "Parity error detected");
> +			clear |= SDW_SCP_INT1_PARITY;
> +		}
> +
> +		if (buf[0] & SDW_SCP_INT1_BUS_CLASH) {
> +			dev_err(&slave->dev, "Bus clash error detected");
> +			clear |= SDW_SCP_INT1_BUS_CLASH;
> +		}
> +
> +		/*
> +		 * When bus clash or parity errors are detected, such errors
> +		 * are unlikely to be recoverable errors.
> +		 * TODO: In such scenario, reset bus. Make this configurable
> +		 * via sysfs property with bus reset being the default.
> +		 */
> +
> +		if (buf[0] & SDW_SCP_INT1_IMPL_DEF) {
> +			dev_dbg(&slave->dev, "Slave impl defined interrupt\n");
> +			clear |= SDW_SCP_INT1_IMPL_DEF;
> +			slave_notify = true;
> +		}
> +
> +		/* Check port 0 - 4 interrupts */
> +		port = buf[0] & SDW_SCP_INT1_PORT0_3;
> +
> +		/* To get port number corresponding to bits, shift it */
> +		port = port >> SDW_REG_SHIFT(SDW_SCP_INT1_PORT0_3);
> +		for_each_set_bit(bit, &port, 8) {
> +			sdw_handle_port_interrupt(slave, bit,
> +						&port_status[bit]);
> +
> +		}
> +
> +		/* Check if cascade 2 interrupt is present */
> +		if (buf[0] & SDW_SCP_INT1_SCP2_CASCADE) {
> +			port = buf[1] & SDW_SCP_INTSTAT2_PORT4_10;
> +			for_each_set_bit(bit, &port, 8) {
> +				/* scp2 ports start from 4 */
> +				port_num = bit + 3;
> +				sdw_handle_port_interrupt(slave,
> +						port_num,
> +						&port_status[port_num]);
> +			}
> +		}
> +
> +		/* now check last cascade */
> +		if (buf[1] & SDW_SCP_INTSTAT2_SCP3_CASCADE) {
> +			port = buf[2] & SDW_SCP_INTSTAT3_PORT11_14;
> +			for_each_set_bit(bit, &port, 8) {
> +				/* scp3 ports start from 11 */
> +				port_num = bit + 10;
> +				sdw_handle_port_interrupt(slave,
> +						port_num,
> +						&port_status[port_num]);
> +			}
> +		}
> +
> +		/* Update the Slave driver */
> +		if (slave_notify && (slave->ops) &&
> +					(slave->ops->interrupt_callback)) {
> +			struct sdw_slave_intr_status slave_intr;
> +
> +			slave_intr.control_port = clear;
> +			memcpy(slave_intr.port, &port_status,
> +						sizeof(slave_intr.port));
> +
> +			slave->ops->interrupt_callback(slave, &slave_intr);
> +		}
> +
> +		/* Ack interrupt */
> +		ret = sdw_write(slave, SDW_SCP_INT1, clear);
> +		if (ret < 0) {
> +			dev_err(slave->bus->dev,
> +					"SDW_SCP_INT1 write failed:%d", ret);
> +			return ret;
> +		}
> +
> +		/*
> +		 * Read status again to ensure no new interrupts arrived
> +		 * while servicing interrupts
> +		 */
> +		ret = sdw_nread(slave, SDW_SCP_INT1, 3, buf);
> +		if (ret < 0) {
> +			dev_err(slave->bus->dev,
> +					"SDW_SCP_INT1 read failed:%d", ret);
> +			return ret;
> +		}
> +
> +		/* Make sure no interrupts are pending */
> +		stat = buf[0] || buf[1] || buf[2];
> +
> +		/*
> +		 * Exit loop if Slave is continuously in ALERT state even
> +		 * after servicing the interrupt multiple times.
> +		 */
> +		count++;
> +
> +		/* we can get alerts while processing so keep retrying */
> +	} while (stat != 0 && count < SDW_READ_INTR_CLEAR_RETRY);

so that's a different case from what is done above, here you are making 
a conscious decision to re-read the interrupt status, it's got nothing 
to do with the spec requirements and you'd probably want a different 
RETRY value.

> +
> +	if (count == SDW_READ_INTR_CLEAR_RETRY)
> +		dev_warn(slave->bus->dev, "Reached MAX_RETRY on alert read");
> +
> +	return ret;
> +}
> +
> +static int sdw_update_slave_status(struct sdw_slave *slave,
> +				enum sdw_slave_status status)
> +{
> +	if ((slave->ops) && (slave->ops->update_status))
> +		return slave->ops->update_status(slave, status);
> +
> +	return 0;
> +}
> +
> +/**
> + * sdw_handle_slave_status() - Handle Slave status
> + * @bus: SDW bus instance
> + * @status: Status for all Slave(s)
> + */
> +int sdw_handle_slave_status(struct sdw_bus *bus,
> +			enum sdw_slave_status status[])
> +{
> +	struct sdw_slave *slave;
> +	int i, ret = 0;
> +
> +	if (status[0] == SDW_SLAVE_ATTACHED) {
> +		ret = sdw_program_device_num(bus);
> +		if (ret)
> +			dev_err(bus->dev, "Slave attach failed: %d", ret);
> +	}
> +
> +	/* Continue to check other slave statuses */
> +	for (i = 1; i <= SDW_MAX_DEVICES; i++) {
> +		mutex_lock(&bus->bus_lock);
> +		if (test_bit(i, bus->assigned) == false) {
> +			mutex_unlock(&bus->bus_lock);
> +			continue;
> +		}
> +		mutex_unlock(&bus->bus_lock);
> +
> +		slave = sdw_get_slave(bus, i);
> +		if (!slave)
> +			continue;
> +
> +		switch (status[i]) {
> +		case SDW_SLAVE_UNATTACHED:
> +			if (slave->status == SDW_SLAVE_UNATTACHED)
> +				break;
> +
> +			sdw_modify_slave_status(slave, SDW_SLAVE_UNATTACHED);
> +			break;
> +
> +		case SDW_SLAVE_ALERT:
> +			ret = sdw_handle_slave_alerts(slave);
> +			if (ret)
> +				dev_err(bus->dev,
> +					"Slave %d alert handling failed: %d",
> +					i, ret);
> +			break;
> +
> +		case SDW_SLAVE_ATTACHED:
> +			if (slave->status == SDW_SLAVE_ATTACHED)
> +				break;
> +
> +			sdw_initialize_slave(slave);
> +			sdw_modify_slave_status(slave, SDW_SLAVE_ATTACHED);
> +
> +			break;
> +
> +		default:
> +			dev_err(bus->dev, "Invalid slave %d status:%d",
> +							i, status[i]);
> +			break;
> +		}
> +
> +		ret = sdw_update_slave_status(slave, status[i]);
> +		if (ret)
> +			dev_err(slave->bus->dev,
> +				"Update Slave status failed:%d", ret);
> +
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(sdw_handle_slave_status);
> diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
> index b491e86f2c4c..463fecb02563 100644
> --- a/drivers/soundwire/bus.h
> +++ b/drivers/soundwire/bus.h
> @@ -45,6 +45,8 @@ struct sdw_msg {
>   	bool page;
>   };
>   
> +#define SDW_READ_INTR_CLEAR_RETRY	10
> +
>   int sdw_transfer(struct sdw_bus *bus, struct sdw_slave *slave,
>   			struct sdw_msg *msg);
>   int sdw_transfer_defer(struct sdw_bus *bus, struct sdw_slave *slave,
> diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
> index 09619d042909..861a910911b6 100644
> --- a/include/linux/soundwire/sdw.h
> +++ b/include/linux/soundwire/sdw.h
> @@ -323,11 +323,28 @@ struct sdw_slave_id {
>   };
>   
>   /**
> + * struct sdw_slave_intr_status - Slave interrupt status
> + * @control_port: control port status
> + * @port: data port status
> + */
> +struct sdw_slave_intr_status {
> +	u8 control_port;
> +	u8 port[14];
> +};
> +
> +/**
>    * struct sdw_slave_ops - Slave driver callback ops
>    * @read_prop: Read Slave properties
> + * @interrupt_callback: Device interrupt notification (invoked in thread
> + * context)
> + * @update_status: Update Slave status
>    */
>   struct sdw_slave_ops {
>   	int (*read_prop)(struct sdw_slave *sdw);
> +	int (*interrupt_callback)(struct sdw_slave *slave,
> +			struct sdw_slave_intr_status *status);
> +	int (*update_status)(struct sdw_slave *slave,
> +			enum sdw_slave_status status);
>   };
>   
>   /**
> @@ -377,6 +394,9 @@ struct sdw_driver {
>   int sdw_handle_slave_status(struct sdw_bus *bus,
>   			enum sdw_slave_status status[]);
>   
> +int sdw_handle_slave_status(struct sdw_bus *bus,
> +			enum sdw_slave_status status[]);
> +
>   /*
>    * SDW master structures and APIs
>    */
> 

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