linux-kernel - Re: [PATCH v3 4/7] Input: synaptics-rmi4

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Message-ID: <Z882vDOOac0kMKg9@google.com>
Date: Mon, 10 Mar 2025 12:00:12 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: david@...t.cz
Cc: 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>,
	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: Re: [PATCH v3 4/7] Input: synaptics-rmi4 - f55: handle zero
 electrode count

On Sat, Mar 08, 2025 at 03:08:40PM +0100, David Heidelberg via B4 Relay wrote:
> 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;

0 here means "successfully detected" and will result in F55 probe
succeeding. I expect you want -EINVAL or -ENODEV here.

Thanks.

-- 
Dmitry