iio: dac: adi-axi-dac: support debugfs direct_reg_access

Make it possible to read/write registers on the backend using the
debugfs interface for it.
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240806-dev-backend-dac-direct-reg-access-v1-1-b84a6e8ee8a0@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/adi-axi-dac.c

@@ -507,6 +507,17 @@ static int axi_dac_set_sample_rate(struct iio_backend *back, unsigned int chan,
 	return 0;
 }
 
+static int axi_dac_reg_access(struct iio_backend *back, unsigned int reg,
+			      unsigned int writeval, unsigned int *readval)
+{
+	struct axi_dac_state *st = iio_backend_get_priv(back);
+
+	if (readval)
+		return regmap_read(st->regmap, reg, readval);
+
+	return regmap_write(st->regmap, reg, writeval);
+}
+
 static const struct iio_backend_ops axi_dac_generic_ops = {
 	.enable = axi_dac_enable,
 	.disable = axi_dac_disable,
@@ -517,6 +528,7 @@ static const struct iio_backend_ops axi_dac_generic_ops = {
 	.ext_info_get = axi_dac_ext_info_get,
 	.data_source_set = axi_dac_data_source_set,
 	.set_sample_rate = axi_dac_set_sample_rate,
+	.debugfs_reg_access = iio_backend_debugfs_ptr(axi_dac_reg_access),
 };
 
 static const struct iio_backend_info axi_dac_generic = {