On Wed, Feb 28, 2018 at 8:43 PM, Rodrigo Rivas Costa
[off-list ref] wrote:

This device has a feature report to send and receive commands.
Use it to get the serial number and set the device's uniq value.

 #include <linux/module.h>
 #include <linux/workqueue.h>
 #include <linux/rcupdate.h>

+#include <linux/delay.h>

Better to keep it somehow sorted (yes, I see it's not originally, but
better to squeeze new header to the most ordered part).

+       char serial_no[11];

11 is a magic.

 };

+static int steam_recv_report(struct steam_device *steam,
+               u8 *data, int size)
+{
+       struct hid_report *r;
+       u8 *buf;
+       int ret;
+
+       r = steam->hdev->report_enum[HID_FEATURE_REPORT].report_id_hash[0];
+       if (hid_report_len(r) < 64)
+               return -EINVAL;

+ empty line.

+       buf = hid_alloc_report_buf(r, GFP_KERNEL);
+       if (!buf)
+               return -ENOMEM;
+
+       /*
+        * The report ID is always 0, so strip the first byte from the output.
+        * hid_report_len() is not counting the report ID, so +1 to the length
+        * or else we get a EOVERFLOW. We are safe from a buffer overflow
+        * because hid_alloc_report_buf() allocates +7 bytes.
+        */
+       ret = hid_hw_raw_request(steam->hdev, 0x00,
+                       buf, hid_report_len(r) + 1,
+                       HID_FEATURE_REPORT, HID_REQ_GET_REPORT);
+       if (ret > 0)
+               memcpy(data, buf + 1, min(size, ret - 1));
+       kfree(buf);
+       return ret;
+}
+
+static int steam_send_report(struct steam_device *steam,
+               u8 *cmd, int size)
+{
+       struct hid_report *r;
+       u8 *buf;
+       int retry;
+       int ret;
+
+       r = steam->hdev->report_enum[HID_FEATURE_REPORT].report_id_hash[0];
+       if (hid_report_len(r) < 64)
+               return -EINVAL;

+empty line.

+       buf = hid_alloc_report_buf(r, GFP_KERNEL);
+       if (!buf)
+               return -ENOMEM;
+
+       /* The report ID is always 0 */
+       memcpy(buf + 1, cmd, size);
+
+       /*
+        * Sometimes the wireless controller fails with EPIPE
+        * when sending a feature report.
+        * Doing a HID_REQ_GET_REPORT and waiting for a while
+        * seems to fix that.
+        */

+       for (retry = 0; retry < 10; ++retry) {
+               ret = hid_hw_raw_request(steam->hdev, 0,
+                               buf, size + 1,
+                               HID_FEATURE_REPORT, HID_REQ_SET_REPORT);
+               if (ret != -EPIPE)
+                       break;
+               steam_recv_report(steam, NULL, 0);
+               msleep(50);
+       }

Personally I consider do{}while in case of "timeout loops" much easier to parse.

unsigned int retry = 10;
...

do {
...
} while (--retry);

+       kfree(buf);
+       if (ret < 0)
+               hid_err(steam->hdev, "%s: error %d (%*ph)\n", __func__,
+                               ret, size, cmd);
+       return ret;
+}
+
+static int steam_get_serial(struct steam_device *steam)
+{
+       /*
+        * Send: 0xae 0x15 0x01
+        * Recv: 0xae 0x15 0x01 serialnumber (10 chars)
+        */
+       int ret;
+       u8 cmd[] = {0xae, 0x15, 0x01};

+       u8 reply[14];
+
+       ret = steam_send_report(steam, cmd, sizeof(cmd));
+       if (ret < 0)
+               return ret;
+       ret = steam_recv_report(steam, reply, sizeof(reply));
+       if (ret < 0)
+               return ret;

+       reply[13] = 0;
+       strcpy(steam->serial_no, reply + 3);

strlcpy()

+       return 0;
+}

-- 
With Best Regards,
Andy Shevchenko