iio: xilinx-xadc: Add basic support for Ultrascale System Monitor

The xilinx-xadc IIO driver currently has support for the XADC in the Xilinx
7 series FPGAs. The system-monitor is the equivalent to the XADC in the
Xilinx UltraScale and UltraScale+ FPGAs.

The IP designers did a good job at maintaining backwards compatibility and
only minor changes are required to add basic support for the system-monitor
core.

The non backwards compatible changes are:
  * Register map offset was moved from 0x200 to 0x400
  * Only one ADC compared to two in the XADC
  * 10 bit ADC instead of 12 bit ADC
  * Two of the channels monitor different supplies

Add the necessary logic to accommodate these changes to support the
system-monitor in the XADC driver.

Note that this patch does not include support for some new features found
in the system-monitor like additional alarms, user supply monitoring and
secondary system-monitor access. This might be added at a later time.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Tested-by: Anand Ashok Dumbre <anandash@xilinx.com>
Reviewed-by: Anand Ashok Dumbre <anandash@xilinx.com>
Link: https://lore.kernel.org/r/20200922134624.13191-2-lars@metafoo.deSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/Kconfig

@@ -1228,8 +1228,15 @@ config XILINX_XADC
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
 	help
-	  Say yes here to have support for the Xilinx XADC. The driver does support
-	  both the ZYNQ interface to the XADC as well as the AXI-XADC interface.
+	  Say yes here to have support for the Xilinx 7 Series XADC or
+	  UltraScale/UltraScale+ System Management Wizard.
+
+	  For the 7 Series the driver does support both the ZYNQ interface
+	  to the XADC as well as the AXI-XADC interface.
+
+	  The driver also support the Xilinx System Management Wizard IP core
+	  that can be used to access the System Monitor ADC on the Xilinx
+	  UltraScale and UltraScale+ FPGAs.
 
 	  The driver can also be build as a module. If so, the module will be called
 	  xilinx-xadc.

drivers/iio/adc/xilinx-xadc-events.c

@@ -155,9 +155,6 @@ int xadc_write_event_config(struct iio_dev *indio_dev,
 	return ret;
 }
 
-/* Register value is msb aligned, the lower 4 bits are ignored */
-#define XADC_THRESHOLD_VALUE_SHIFT 4
-
 int xadc_read_event_value(struct iio_dev *indio_dev,
 	const struct iio_chan_spec *chan, enum iio_event_type type,
 	enum iio_event_direction dir, enum iio_event_info info,
@@ -177,7 +174,8 @@ int xadc_read_event_value(struct iio_dev *indio_dev,
 		return -EINVAL;
 	}
 
-	*val >>= XADC_THRESHOLD_VALUE_SHIFT;
+	/* MSB aligned */
+	*val >>= 16 - chan->scan_type.realbits;
 
 	return IIO_VAL_INT;
 }
@@ -191,7 +189,8 @@ int xadc_write_event_value(struct iio_dev *indio_dev,
 	struct xadc *xadc = iio_priv(indio_dev);
 	int ret = 0;
 
-	val <<= XADC_THRESHOLD_VALUE_SHIFT;
+	/* MSB aligned */
+	val <<= 16 - chan->scan_type.realbits;
 
 	if (val < 0 || val > 0xffff)
 		return -EINVAL;

drivers/iio/adc/xilinx-xadc.h

@@ -70,6 +70,11 @@ struct xadc {
 	int irq;
 };
 
+enum xadc_type {
+	XADC_TYPE_S7, /* Series 7 */
+	XADC_TYPE_US, /* UltraScale and UltraScale+ */
+};
+
 struct xadc_ops {
 	int (*read)(struct xadc *xadc, unsigned int reg, uint16_t *val);
 	int (*write)(struct xadc *xadc, unsigned int reg, uint16_t val);
@@ -80,6 +85,7 @@ struct xadc_ops {
 	irqreturn_t (*interrupt_handler)(int irq, void *devid);
 
 	unsigned int flags;
+	enum xadc_type type;
 };
 
 static inline int _xadc_read_adc_reg(struct xadc *xadc, unsigned int reg,