[RFC rtw-next 2/2] wifi: rtw89: usb: add sysfs write example

[Ping-Ke Shih <pkshih@realtek.com>]

From: Johnson Tsai <wenjie.tsai@realtek.com>

Add a simple echo_sum sysfs attribute on the USB interface device as
an RFC example for discussing whether a writable sysfs interface is
acceptable for this driver.

The attribute accepts two integers from userspace, stores their sum in
driver private data, and exposes the result.

Signed-off-by: Johnson Tsai <wenjie.tsai@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
---
 drivers/net/wireless/realtek/rtw89/usb.c | 38 ++++++++++++++++++++++++
 drivers/net/wireless/realtek/rtw89/usb.h |  2 ++
 2 files changed, 40 insertions(+)

diff --git a/drivers/net/wireless/realtek/rtw89/usb.c b/drivers/net/wireless/realtek/rtw89/usb.c
index 53dcb84af5c0..566618e9f3b8 100644
--- a/drivers/net/wireless/realtek/rtw89/usb.c
+++ b/drivers/net/wireless/realtek/rtw89/usb.c
@@ -1059,6 +1059,43 @@ static void rtw89_usb_intf_deinit(struct rtw89_dev *rtwdev,
 	usb_set_intfdata(intf, NULL);
 }
 
+static ssize_t echo_sum_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct ieee80211_hw *hw = usb_get_intfdata(intf);
+	struct rtw89_usb *rtwusb;
+
+	if (!hw)
+		return -ENODEV;
+
+	rtwusb = rtw89_usb_priv(hw->priv);
+
+	return sysfs_emit(buf, "%u\n", rtwusb->echo_sum);
+}
+
+static ssize_t echo_sum_store(struct device *dev,
+			      struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct ieee80211_hw *hw = usb_get_intfdata(intf);
+	struct rtw89_usb *rtwusb;
+	int a, b;
+
+	if (!hw)
+		return -ENODEV;
+
+	if (sscanf(buf, "%d %d", &a, &b) != 2)
+		return -EINVAL;
+
+	rtwusb = rtw89_usb_priv(hw->priv);
+	rtwusb->echo_sum = a + b;
+
+	return count;
+}
+static DEVICE_ATTR_ADMIN_RW(echo_sum);
+
 static ssize_t hw_info_show(struct device *dev,
 			    struct device_attribute *attr, char *buf)
 {
@@ -1089,6 +1126,7 @@ static ssize_t hw_info_show(struct device *dev,
 static DEVICE_ATTR_RO(hw_info);
 
 static struct attribute *rtw89_usb_attrs[] = {
+	&dev_attr_echo_sum.attr,
 	&dev_attr_hw_info.attr,
 	NULL,
 };
diff --git a/drivers/net/wireless/realtek/rtw89/usb.h b/drivers/net/wireless/realtek/rtw89/usb.h
index bdf312559743..9eba6264a9a2 100644
--- a/drivers/net/wireless/realtek/rtw89/usb.h
+++ b/drivers/net/wireless/realtek/rtw89/usb.h
@@ -87,6 +87,8 @@ struct rtw89_usb {
 
 	struct sk_buff_head tx_queue[RTW89_TXCH_NUM];
 	atomic_t tx_inflight[RTW89_TXCH_NUM];
+
+	u32 echo_sum;
 };
 
 static inline struct rtw89_usb *rtw89_usb_priv(struct rtw89_dev *rtwdev)
-- 
2.25.1