linux-kernel - [PATCH v3 4/7] Input: synaptics-rmi4 - f55: handle zero electrode count

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Message-Id: <20250308-synaptics-rmi4-v3-4-215d3e7289a2@ixit.cz>
Date: Sat, 08 Mar 2025 15:08:40 +0100
From: David Heidelberg via B4 Relay <devnull+david.ixit.cz@...nel.org>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, "Jason A. Donenfeld" <Jason@...c4.com>, 
 Matthias Schiffer <matthias.schiffer@...tq-group.com>, 
 Vincent Huang <vincent.huang@...synaptics.com>
Cc: linux-input@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, phone-devel@...r.kernel.org, 
 ~postmarketos/upstreaming@...ts.sr.ht, methanal <baclofen@...a.io>, 
 Caleb Connolly <caleb.connolly@...aro.org>
Subject: [PATCH v3 4/7] Input: synaptics-rmi4 - f55: handle zero electrode
 count

From: methanal <baclofen@...a.io>

Some third party ICs claim to support f55 but report an electrode count
of 0. Catch this and bail out early so that we don't confuse the i2c bus
with 0 sized reads.

Signed-off-by: methanal <baclofen@...a.io>
[simplify code, adjust wording]
Signed-off-by: Caleb Connolly <caleb.connolly@...aro.org>
---
 drivers/input/rmi4/rmi_f55.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/input/rmi4/rmi_f55.c b/drivers/input/rmi4/rmi_f55.c
index 488adaca4dd00482cd1106d813b32871092c83a0..ad2ef14ae9f4e897473db43334792cc3de966d52 100644
--- a/drivers/input/rmi4/rmi_f55.c
+++ b/drivers/input/rmi4/rmi_f55.c
@@ -52,6 +52,11 @@ static int rmi_f55_detect(struct rmi_function *fn)

 	f55->num_rx_electrodes = f55->qry[F55_NUM_RX_OFFSET];
 	f55->num_tx_electrodes = f55->qry[F55_NUM_TX_OFFSET];
+	if (!f55->num_rx_electrodes || !f55->num_tx_electrodes) {
+		rmi_dbg(RMI_DEBUG_FN, &fn->dev,
+			"F55 query returned no electrodes, giving up\n");
+		return 0;
+	}

 	f55->cfg_num_rx_electrodes = f55->num_rx_electrodes;
 	f55->cfg_num_tx_electrodes = f55->num_rx_electrodes;

-- 
2.47.2