Input: goodix-berlin - add sysfs interface for reading and writing touch IC registers

Export a sysfs interface that would allow reading and writing touchscreen
IC registers. With this interface many things can be done in usersapce
such as firmware updates. An example tool that utilizes this interface
for performing firmware updates can be found at [1].

[1] https://github.com/goodix/fwupdate_for_berlin_linux

Signed-off-by: Charles Wang <charles.goodix@gmail.com>
Link: https://lore.kernel.org/r/20240514115135.21410-1-charles.goodix@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/goodix_berlin.h

@@ -20,5 +20,6 @@ int goodix_berlin_probe(struct device *dev, int irq, const struct input_id *id,
 			struct regmap *regmap);
 
 extern const struct dev_pm_ops goodix_berlin_pm_ops;
+extern const struct attribute_group *goodix_berlin_groups[];
 
 #endif

drivers/input/touchscreen/goodix_berlin_core.c

@@ -672,6 +672,49 @@ static void goodix_berlin_power_off_act(void *data)
 	goodix_berlin_power_off(cd);
 }
 
+static ssize_t registers_read(struct file *filp, struct kobject *kobj,
+			      struct bin_attribute *bin_attr,
+			      char *buf, loff_t off, size_t count)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct goodix_berlin_core *cd = dev_get_drvdata(dev);
+	int error;
+
+	error = regmap_raw_read(cd->regmap, off, buf, count);
+
+	return error ? error : count;
+}
+
+static ssize_t registers_write(struct file *filp, struct kobject *kobj,
+			       struct bin_attribute *bin_attr,
+			       char *buf, loff_t off, size_t count)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct goodix_berlin_core *cd = dev_get_drvdata(dev);
+	int error;
+
+	error = regmap_raw_write(cd->regmap, off, buf, count);
+
+	return error ? error : count;
+}
+
+static BIN_ATTR_ADMIN_RW(registers, 0);
+
+static struct bin_attribute *goodix_berlin_bin_attrs[] = {
+	&bin_attr_registers,
+	NULL,
+};
+
+static const struct attribute_group goodix_berlin_attr_group = {
+	.bin_attrs = goodix_berlin_bin_attrs,
+};
+
+const struct attribute_group *goodix_berlin_groups[] = {
+	&goodix_berlin_attr_group,
+	NULL,
+};
+EXPORT_SYMBOL_GPL(goodix_berlin_groups);
+
 int goodix_berlin_probe(struct device *dev, int irq, const struct input_id *id,
 			struct regmap *regmap)
 {

drivers/input/touchscreen/goodix_berlin_i2c.c

@@ -64,6 +64,7 @@ static struct i2c_driver goodix_berlin_i2c_driver = {
 		.name = "goodix-berlin-i2c",
 		.of_match_table = goodix_berlin_i2c_of_match,
 		.pm = pm_sleep_ptr(&goodix_berlin_pm_ops),
+		.dev_groups = goodix_berlin_groups,
 	},
 	.probe = goodix_berlin_i2c_probe,
 	.id_table = goodix_berlin_i2c_id,

drivers/input/touchscreen/goodix_berlin_spi.c

@@ -169,6 +169,7 @@ static struct spi_driver goodix_berlin_spi_driver = {
 		.name = "goodix-berlin-spi",
 		.of_match_table = goodix_berlin_spi_of_match,
 		.pm = pm_sleep_ptr(&goodix_berlin_pm_ops),
+		.dev_groups = goodix_berlin_groups,
 	},
 	.probe = goodix_berlin_spi_probe,
 	.id_table = goodix_berlin_spi_ids,