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[PATCH 0/3] Add 'external mode' for GPIO-based FSI master

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  [PATCH 0/3] Add 'external mode' for GPIO-based FSI master Jeremy Kerr <jk@ozlabs.org> - 2017-06-19 11:30 +0200
    [PATCH 2/3] fsi/master-gpio: Add locking around gpio operations during break & link enable Jeremy Kerr <jk@ozlabs.org> - 2017-06-19 11:30 +0200
    [PATCH 3/3] fsi/master-gpio: Add external mode Jeremy Kerr <jk@ozlabs.org> - 2017-06-19 11:30 +0200

#1668933 — [PATCH 0/3] Add 'external mode' for GPIO-based FSI master

This series (on top of current char-misc-next) implements "external
mode" (ie, support for FSI debug devices) for the GPIO-based FSI master
driver.

We implement this control in the GPIO master driver, as it has the
mapping of raw GPIO pins to fsi control signals, and provides a
mechanism for the kernel to retain exclusive access to those GPIOs.

Cheers,


Jeremy

---
Jeremy Kerr (3):
  fsi: Add fsi_master_rescan()
  fsi/master-gpio: Add locking around gpio operations during break &
    link enable
  fsi/master-gpio: Add external mode

 .../ABI/testing/sysfs-driver-fsi-master-gpio       | 10 +++
 drivers/fsi/fsi-core.c                             |  9 ++-
 drivers/fsi/fsi-master-gpio.c                      | 85 +++++++++++++++++++++-
 drivers/fsi/fsi-master.h                           |  2 +
 4 files changed, 102 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-driver-fsi-master-gpio

-- 
2.7.4

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#1668935 — [PATCH 2/3] fsi/master-gpio: Add locking around gpio operations during break & link enable

Currently, we perform GPIO accesses in fsi_master_gpio_break and
fsi_master_link_enable, without holding cmd_lock. This change adds the
appropriate locking.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Christopher Bostic <clbostic@linux.vnet.ibm.com>
---
 drivers/fsi/fsi-master-gpio.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/fsi/fsi-master-gpio.c b/drivers/fsi/fsi-master-gpio.c
index ae26187..a6d602e 100644
--- a/drivers/fsi/fsi-master-gpio.c
+++ b/drivers/fsi/fsi-master-gpio.c
@@ -461,12 +461,14 @@ static int fsi_master_gpio_term(struct fsi_master *_master,
 static int fsi_master_gpio_break(struct fsi_master *_master, int link)
 {
 	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
+	unsigned long flags;
 
 	if (link != 0)
 		return -ENODEV;
 
 	trace_fsi_master_gpio_break(master);
 
+	spin_lock_irqsave(&master->cmd_lock, flags);
 	set_sda_output(master, 1);
 	sda_out(master, 1);
 	clock_toggle(master, FSI_PRE_BREAK_CLOCKS);
@@ -475,6 +477,7 @@ static int fsi_master_gpio_break(struct fsi_master *_master, int link)
 	echo_delay(master);
 	sda_out(master, 1);
 	clock_toggle(master, FSI_POST_BREAK_CLOCKS);
+	spin_unlock_irqrestore(&master->cmd_lock, flags);
 
 	/* Wait for logic reset to take effect */
 	udelay(200);
@@ -497,10 +500,14 @@ static void fsi_master_gpio_init(struct fsi_master_gpio *master)
 static int fsi_master_gpio_link_enable(struct fsi_master *_master, int link)
 {
 	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
+	unsigned long flags;
 
 	if (link != 0)
 		return -ENODEV;
+
+	spin_lock_irqsave(&master->cmd_lock, flags);
 	gpiod_set_value(master->gpio_enable, 1);
+	spin_unlock_irqrestore(&master->cmd_lock, flags);
 
 	return 0;
 }
-- 
2.7.4

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#1668936 — [PATCH 3/3] fsi/master-gpio: Add external mode

This change introduces an 'external mode' for GPIO-based FSI masters,
allowing the clock and data lines to be driven by an external source.
For example, external mode is selected by a user when an external debug
device is attached to the FSI pins.

To do this, we need to set specific states for the trans, mux and enable
gpios, and prevent access to clk & data from the FSI core code (by
returning EBUSY).

External mode is controlled by a sysfs attribute, so add the relevent
information to Documentation/ABI/

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
---
 .../ABI/testing/sysfs-driver-fsi-master-gpio       | 10 +++
 drivers/fsi/fsi-master-gpio.c                      | 78 +++++++++++++++++++++-
 2 files changed, 86 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-driver-fsi-master-gpio

diff --git a/Documentation/ABI/testing/sysfs-driver-fsi-master-gpio b/Documentation/ABI/testing/sysfs-driver-fsi-master-gpio
new file mode 100644
index 0000000..9667bb4
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-fsi-master-gpio
@@ -0,0 +1,10 @@
+What:           /sys/bus/platform/devices/[..]/fsi-master-gpio/external_mode
+Date:           June 2017
+KernelVersion:  4.12
+Contact:        jk@ozlabs.org
+Description:
+                Controls access arbitration for GPIO-based FSI master. A
+		value of 0 (the default) sets normal mode, where the
+		driver performs FSI bus transactions, 1 sets external mode,
+		where the FSI bus is driven externally (for example, by
+		a debug device).
diff --git a/drivers/fsi/fsi-master-gpio.c b/drivers/fsi/fsi-master-gpio.c
index a6d602e..88d26fe 100644
--- a/drivers/fsi/fsi-master-gpio.c
+++ b/drivers/fsi/fsi-master-gpio.c
@@ -59,6 +59,7 @@ struct fsi_master_gpio {
 	struct gpio_desc	*gpio_trans;	/* Voltage translator */
 	struct gpio_desc	*gpio_enable;	/* FSI enable */
 	struct gpio_desc	*gpio_mux;	/* Mux control */
+	bool			external_mode;
 };
 
 #define CREATE_TRACE_POINTS
@@ -411,6 +412,12 @@ static int fsi_master_gpio_xfer(struct fsi_master_gpio *master, uint8_t slave,
 	int rc;
 
 	spin_lock_irqsave(&master->cmd_lock, flags);
+
+	if (master->external_mode) {
+		spin_unlock_irqrestore(&master->cmd_lock, flags);
+		return -EBUSY;
+	}
+
 	serial_out(master, cmd);
 	echo_delay(master);
 	rc = poll_for_response(master, slave, resp_len, resp);
@@ -469,6 +476,10 @@ static int fsi_master_gpio_break(struct fsi_master *_master, int link)
 	trace_fsi_master_gpio_break(master);
 
 	spin_lock_irqsave(&master->cmd_lock, flags);
+	if (master->external_mode) {
+		spin_unlock_irqrestore(&master->cmd_lock, flags);
+		return -EBUSY;
+	}
 	set_sda_output(master, 1);
 	sda_out(master, 1);
 	clock_toggle(master, FSI_PRE_BREAK_CLOCKS);
@@ -497,25 +508,84 @@ static void fsi_master_gpio_init(struct fsi_master_gpio *master)
 	clock_zeros(master, FSI_INIT_CLOCKS);
 }
 
+static void fsi_master_gpio_init_external(struct fsi_master_gpio *master)
+{
+	gpiod_direction_output(master->gpio_mux, 0);
+	gpiod_direction_output(master->gpio_trans, 0);
+	gpiod_direction_output(master->gpio_enable, 1);
+	gpiod_direction_input(master->gpio_clk);
+	gpiod_direction_input(master->gpio_data);
+}
+
 static int fsi_master_gpio_link_enable(struct fsi_master *_master, int link)
 {
 	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
 	unsigned long flags;
+	int rc = -EBUSY;
 
 	if (link != 0)
 		return -ENODEV;
 
 	spin_lock_irqsave(&master->cmd_lock, flags);
-	gpiod_set_value(master->gpio_enable, 1);
+	if (!master->external_mode) {
+		gpiod_set_value(master->gpio_enable, 1);
+		rc = 0;
+	}
 	spin_unlock_irqrestore(&master->cmd_lock, flags);
 
-	return 0;
+	return rc;
+}
+
+static ssize_t external_mode_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct fsi_master_gpio *master = dev_get_drvdata(dev);
+
+	return snprintf(buf, PAGE_SIZE - 1, "%u",
+			master->external_mode ? 1 : 0);
+}
+
+static ssize_t external_mode_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct fsi_master_gpio *master = dev_get_drvdata(dev);
+	unsigned long flags, val;
+	bool external_mode;
+	int err;
+
+	err = kstrtoul(buf, 0, &val);
+	if (err)
+		return err;
+
+	external_mode = !!val;
+
+	spin_lock_irqsave(&master->cmd_lock, flags);
+
+	if (external_mode == master->external_mode) {
+		spin_unlock_irqrestore(&master->cmd_lock, flags);
+		return count;
+	}
+
+	master->external_mode = external_mode;
+	if (master->external_mode)
+		fsi_master_gpio_init_external(master);
+	else
+		fsi_master_gpio_init(master);
+	spin_unlock_irqrestore(&master->cmd_lock, flags);
+
+	fsi_master_rescan(&master->master);
+
+	return count;
 }
 
+static DEVICE_ATTR(external_mode, 0664,
+		external_mode_show, external_mode_store);
+
 static int fsi_master_gpio_probe(struct platform_device *pdev)
 {
 	struct fsi_master_gpio *master;
 	struct gpio_desc *gpio;
+	int rc;
 
 	master = devm_kzalloc(&pdev->dev, sizeof(*master), GFP_KERNEL);
 	if (!master)
@@ -572,6 +642,10 @@ static int fsi_master_gpio_probe(struct platform_device *pdev)
 
 	fsi_master_gpio_init(master);
 
+	rc = device_create_file(&pdev->dev, &dev_attr_external_mode);
+	if (rc)
+		return rc;
+
 	return fsi_master_register(&master->master);
 }
 
-- 
2.7.4

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