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@xxxxxxxxxxxxx>
> ---
> 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
>
>
