[PATCH v3 05/16] HID: ft260: fix sysfs store failure notice for big numbers

[Michael Zaidman <michael.zaidman@gmail.com>]

FT260_ATTR_STORE returned the feature-report transfer length from
ft260_hid_feature_report_set() instead of the sysfs write size. For
values like 1000, userspace writes more bytes than the HID report
length, so the VFS retries the remainder and reports "Invalid argument"
even though the attribute was applied correctly:

  $ echo 1000 > .../clock
  bash: line 1: echo: write error: Invalid argument
  $ cat .../clock
  1000

Return count when the feature report succeeds, so the full write is
consumed, and the error when it fails.

Parse a 16-bit attribute, such as clock, into a u16 and convert it with
cpu_to_le16(), because the report field is little endian. Before, the
value was parsed straight into the __le16 field, which is wrong on a
big-endian CPU.

Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>

---
v2:
Fixes for the issues reported by Sashiko:
- A failed feature report is not reported as success.
- A 16-bit attribute is converted with cpu_to_le16(), so it is correct
  on a big-endian CPU.

v3:
Subject reworded after the original out-of-tree commit, "Get rid of
sysfs store big numbers failure notice". The v2 subject read as if the
patch hid big values. No i2c: prefix, because FT260_ATTR_STORE serves
all store attributes, not only the I2C ones.
---
 drivers/hid/hid-ft260.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index 50389b3e79d8..13dbff661fab 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -1484,56 +1484,60 @@ static void ft260_attr_dummy_func(struct hid_device *hdev, u8 req, u16 value)
 	}
 
 #define FT260_SSTAT_ATTR_SHOW(name)					       \
 		FT260_ATTR_SHOW(name, ft260_get_system_status_report,	       \
 				FT260_SYSTEM_SETTINGS, u8, ft260_byte_show)
 
 #define FT260_I2CST_ATTR_SHOW(name)					       \
 		FT260_ATTR_SHOW(name, ft260_get_i2c_status_report,	       \
 				FT260_I2C_STATUS, __le16, ft260_word_show)
 
-#define FT260_ATTR_STORE(name, reptype, id, req, type, ctype, strtou, func)    \
+#define FT260_STORE_NATIVE(v) (v)
+
+#define FT260_ATTR_STORE(name, reptype, id, req, type, strtou, func, conv)     \
 	static ssize_t name##_store(struct device *kdev,		       \
 				    struct device_attribute *attr,	       \
 				    const char *buf, size_t count)	       \
 	{								       \
 		struct reptype rep;					       \
 		struct hid_device *hdev = to_hid_device(kdev);		       \
 		struct ft260_device *dev = hid_get_drvdata(hdev);	       \
 		type name;						       \
 		int ret;						       \
 									       \
-		if (!strtou(buf, 10, (ctype *)&name)) {			       \
-			rep.name = name;				       \
+		if (!strtou(buf, 10, &name)) {				       \
+			rep.name = conv(name);				       \
 			rep.report = id;				       \
 			rep.request = req;				       \
 			mutex_lock(&dev->lock);				       \
 			ret = ft260_hid_feature_report_set(hdev, (u8 *)&rep,   \
 							   sizeof(rep));       \
 			if (ret < 0)					       \
 				hid_err(hdev, "%s: failed!\n", __func__);      \
-			else						       \
+			else {						       \
 				func(hdev, req, name);			       \
+				ret = count;				       \
+			}						       \
 			mutex_unlock(&dev->lock);			       \
 		} else {						       \
 			ret = -EINVAL;					       \
 		}							       \
 		return ret;						       \
 	}
 
 #define FT260_BYTE_ATTR_STORE(name, reptype, req, func)			       \
 		FT260_ATTR_STORE(name, reptype, FT260_SYSTEM_SETTINGS, req,    \
-				 u8, u8, kstrtou8, func)
+				 u8, kstrtou8, func, FT260_STORE_NATIVE)
 
 #define FT260_WORD_ATTR_STORE(name, reptype, req, func)			       \
 		FT260_ATTR_STORE(name, reptype, FT260_SYSTEM_SETTINGS, req,    \
-				 __le16, u16, kstrtou16, func)
+				 u16, kstrtou16, func, cpu_to_le16)
 
 FT260_SSTAT_ATTR_SHOW(chip_mode);
 static DEVICE_ATTR_RO(chip_mode);
 
 FT260_SSTAT_ATTR_SHOW(pwren_status);
 static DEVICE_ATTR_RO(pwren_status);
 
 FT260_SSTAT_ATTR_SHOW(suspend_status);
 static DEVICE_ATTR_RO(suspend_status);
 
-- 
2.43.0