Re: [PATCH 2/3] HID: valve-index: Reboot headset on system power transitions

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Incorrect buffer formatting and report ID targeting in `hid_hw_raw_request` fallback for an unnumbered HID report.
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commit 4526fbce2701e5a40089fba6ae186ded76bc0864
Author: Mario Limonciello [off-list ref]
Subject: HID: valve-index: Reboot headset on system power transitions

This commit introduces a new HID driver for the Valve Index headset to
reboot it on system power transitions. It sends a specific 64-byte report
to recover the EDID service after a DisplayPort link shutdown.

Link: https://github.com/ValveSoftware/SteamVR-for-Linux/issues/939

[ ... ]

+static void valve_index_reboot(struct hid_device *hdev, bool wake)
+{
+	u8 *report;
+	int ret;
+
+	if (!valve_index_has_reboot_report(hdev))
+		return;
+
+	/* USB transfer buffers must be DMA-able, so not on the stack. */
+	report = kzalloc(VALVE_INDEX_REPORT_SIZE, GFP_KERNEL);
+	if (!report)
+		return;
+	report[0] = VALVE_INDEX_REBOOT_REPORT_ID;

[Severity: Medium]
Is the report buffer sized correctly for an unnumbered report fallback?

The HID core and usbhid transport expect unnumbered report buffers to be
prefixed with a dummy 0x00 byte (so payload size + 1) for control transfers.
Allocating exactly 64 bytes and placing the payload command at index 0 might
break control transfer formatting in usbhid_set_raw_report if the fallback
path below is taken.

[ ... ]

+	/* Use the same interrupt-out then SET_REPORT fallback as hidraw. */
+	ret = hid_hw_output_report(hdev, report, VALVE_INDEX_REPORT_SIZE);
+	if (ret == -ENOSYS)
+		ret = hid_hw_raw_request(hdev, report[0], report,
+					 VALVE_INDEX_REPORT_SIZE,
+					 HID_OUTPUT_REPORT, HID_REQ_SET_REPORT);

[Severity: Medium]
Does this properly target the unnumbered report during the fallback?

By passing report[0] (which contains 0x16) as the reportnum argument, the
fallback control transfer will target Output Report ID 0x16 instead of the
required unnumbered report (ID 0). If hid_hw_output_report returns -ENOSYS
and this fallback is taken, the headset might reject the transfer, causing
the reboot command to fail.

+	if (ret < 0)
+		hid_warn(hdev, "failed to reboot headset: %d\n", ret);

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260910170254.833871-1-mario.limonciello@amd.com?part=2