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From: Rob Herring <robh@kernel.org>
To: Eddie James <eajames@linux.ibm.com>
Cc: linux-i2c@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, peda@axentia.se
Subject: Re: [PATCH v2 2/2] i2c: mux: pca954x: Support multiple devices on a single reset line
Date: Mon, 2 Aug 2021 14:46:02 -0600	[thread overview]
Message-ID: <YQhZimPDbNJk5nbR@robh.at.kernel.org> (raw)
In-Reply-To: <20210727160315.15575-3-eajames@linux.ibm.com>

On Tue, Jul 27, 2021 at 11:03:15AM -0500, Eddie James wrote:
> Some systems connect several PCA954x devices to a single reset GPIO. For
> these devices to get out of reset and probe successfully, each device must
> defer the probe until the GPIO has been hogged. Accomplish this by
> attempting to grab a new "reset-shared-hogged" devicetree property, but
> expect it to fail with EPROBE_DEFER or EBUSY.
> 
> Signed-off-by: Eddie James <eajames@linux.ibm.com>
> ---
>  drivers/i2c/muxes/i2c-mux-pca954x.c | 46 +++++++++++++++++++++++------
>  1 file changed, 37 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 4ad665757dd8..376b54ffb590 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -434,15 +434,43 @@ static int pca954x_probe(struct i2c_client *client,
>  	i2c_set_clientdata(client, muxc);
>  	data->client = client;
>  
> -	/* Reset the mux if a reset GPIO is specified. */
> -	gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
> -	if (IS_ERR(gpio))
> -		return PTR_ERR(gpio);
> -	if (gpio) {
> -		udelay(1);
> -		gpiod_set_value_cansleep(gpio, 0);
> -		/* Give the chip some time to recover. */
> -		udelay(1);
> +	/*
> +	 * Grab the shared, hogged gpio that controls the mux reset. We expect
> +	 * this to fail with either EPROBE_DEFER or EBUSY. The only purpose of
> +	 * trying to get it is to make sure the gpio controller has probed up
> +	 * and hogged the line to take the mux out of reset, meaning that the
> +	 * mux is ready to be probed up. Don't try and set the line any way; in
> +	 * the event we actually successfully get the line (if it wasn't
> +	 * hogged) then we immediately release it, since there is no way to
> +	 * sync up the line between muxes.
> +	 */
> +	gpio = gpiod_get_optional(dev, "reset-shared-hogged", 0);
> +	if (IS_ERR(gpio)) {
> +		ret = PTR_ERR(gpio);
> +		if (ret != -EBUSY)
> +			return ret;

Why can't you just do this with the existing 'reset-gpios' property? 
What's the usecase where you'd want to fail probe because EBUSY other 
than an error in your DT.

> +	} else {
> +		if (gpio) {
> +			/* This is really a problem since now we don't know the
> +			 * state of the gpio. Log a warning and keep trying to
> +			 * probe the mux just in case it works.
> +			 */
> +			dev_warn(dev, "got hogged reset line, expect error\n");
> +			gpiod_put(gpio);
> +		} else {
> +			/* Reset the mux if a reset GPIO is specified. */
> +			gpio = devm_gpiod_get_optional(dev, "reset",
> +						       GPIOD_OUT_HIGH);
> +			if (IS_ERR(gpio))
> +				return PTR_ERR(gpio);
> +
> +			if (gpio) {
> +				udelay(1);
> +				gpiod_set_value_cansleep(gpio, 0);
> +				/* Give the chip some time to recover. */
> +				udelay(1);
> +			}
> +		}
>  	}
>  
>  	data->chip = device_get_match_data(dev);
> -- 
> 2.27.0
> 
> 

  reply	other threads:[~2021-08-02 20:46 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 16:03 [PATCH v2 0/2] " Eddie James
2021-07-27 16:03 ` [PATCH v2 1/2] dt-bindings: i2c: i2c-mux-pca954x: Define the reset-shared-hogged gpio Eddie James
2021-07-27 16:03 ` [PATCH v2 2/2] i2c: mux: pca954x: Support multiple devices on a single reset line Eddie James
2021-08-02 20:46   ` Rob Herring [this message]
2021-08-02 21:51     ` Eddie James
2021-08-02 22:35       ` Rob Herring
2021-08-04  7:50       ` Peter Rosin
2021-08-04 13:28         ` Rob Herring
2021-08-04 15:12           ` Eddie James
2021-08-04 16:35             ` Rob Herring

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