linux-kernel - [PATCH 2/3] HID: i2c-hid: Retry HID descriptor read to wake up STM devices

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Date: Mon, 15 Apr 2024 19:04:12 +0200
From: Kenny Levinsen <kl@...wtf>
To: Jiri Kosina <jikos@...nel.org>,
	Dmitry Torokhov <dtor@...omium.org>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Douglas Anderson <dianders@...omium.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Maxime Ripard <mripard@...nel.org>,
	Kai-Heng Feng <kai.heng.feng@...onical.com>,
	Johan Hovold <johan+linaro@...nel.org>,
	linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Radoslaw Biernacki <rad@...omium.org>,
	Lukasz Majczak <lma@...omium.org>
Cc: Kenny Levinsen <kl@...wtf>
Subject: [PATCH 2/3] HID: i2c-hid: Retry HID descriptor read to wake up STM devices

Some STM microcontrollers need some time after rising clock edge in
order to come out of their deep sleep state. This in turn means that the
first command send to them timeout and fail with EREMOTEIO.

Retry once on EREMOTEIO to see if the device came alive, otherwise treat
the error as if no device was present like before.

Link: https://lore.kernel.org/all/20240405102436.3479210-1-lma@chromium.org/#t
Signed-off-by: Kenny Levinsen <kl@...wtf>
---
 drivers/hid/i2c-hid/i2c-hid-core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 515a80dbf6c7..ac661199d2c8 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -1010,7 +1010,15 @@ static int __i2c_hid_core_probe(struct i2c_hid *ihid)
 	struct hid_device *hid = ihid->hid;
 	int ret;
 
+	/*
+	 * Some STM-based devices need some time after a rising clock edge to
+	 * wake from deep sleep, which in turn means that our first command
+	 * will fail EREMOTEIO. Retry the command in this case.
+	 */
 	ret = i2c_hid_fetch_hid_descriptor(ihid);
+	if (ret == -EREMOTEIO)
+		ret = i2c_hid_fetch_hid_descriptor(ihid);
+
 	if (ret == -EREMOTEIO) {
 		i2c_hid_dbg(ihid, "nothing at this address: %d\n", ret);
 		return -ENXIO;
-- 
2.44.0