On Mon, 2021-08-02 at 14:46 -0600, Rob Herring wrote:
> 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.
Hi, thanks for the reply.
Are you suggesting I use "reset-gpios" and change the driver to ignore
EBUSY? I don't know any other usecase, I just didn't think it would be
acceptable to ignore EBUSY on that, but perhaps it is a better
solution.
Thanks,
Eddie
>
> > + } 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
> >
> >
