Message-ID: <20160906210735.6wl5x2mdhnhdnh7y@pengutronix.de>
Date:   Tue, 6 Sep 2016 23:07:35 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Leo Li <pku.leo@...il.com>
Cc:     Li Yang <leoyang.li@....com>, Gao Pan <pandy.gao@....com>,
        Wolfram Sang <wsa@...-dreams.de>,
        lkml <linux-kernel@...r.kernel.org>, linux-gpio@...r.kernel.org,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5] i2c: imx: make bus recovery through pinctrl optional

On Tue, Sep 06, 2016 at 03:06:41PM -0500, Leo Li wrote:
> On Tue, Sep 6, 2016 at 1:58 PM, Uwe Kleine-König
> <u.kleine-koenig@...gutronix.de> wrote:
> > On Fri, Aug 19, 2016 at 05:05:22PM -0500, Li Yang wrote:
> >> Since commit 1c4b6c3bcf30 ("i2c: imx: implement bus recovery") the
> >> driver starts to use gpio/pinctrl to do i2c bus recovery.  But pinctrl
> >> is not always available for platforms with this controller such as ls1021a
> >> and ls1043a, and the device tree binding also mentioned this gpio based
> >> recovery mechanism as optional.  The patch makes it really optional that
> >> the probe function won't bailout but just disable the bus recovery function
> >> when pinctrl is not available.
> >>
> >> Signed-off-by: Li Yang <leoyang.li@....com>
> >> Cc: Gao Pan <pandy.gao@....com>
> >> Cc: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> >> Acked-by: Linus Walleij <linus.walleij@...aro.org>
> >> ---
> >> v5:
> >> Revert the last minute change of recovery info initialization timing, it
> >> will cause problem if initialized after i2c_add_numbered_adapter()
> >>
> >> v4:
> >> Remove the use of IS_ERR_OR_NULL
> >> Move the condition judgement to i2c_imx_init_recovery_info()
> >> Change the timing of recovery initialization to be after bus registration
> >>
> >> v3:
> >> Rebased to Wolfram's for-next branch
> >> Added acked-by from Linus Walleij
> >> Update to use new nxp email addresses due to company merge
> >>
> >>  drivers/i2c/busses/i2c-imx.c | 15 ++++++++++++++-
> >>  1 file changed, 14 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> >> index 1844bc9..7ae7992 100644
> >> --- a/drivers/i2c/busses/i2c-imx.c
> >> +++ b/drivers/i2c/busses/i2c-imx.c
> >> @@ -989,6 +989,15 @@ static void i2c_imx_init_recovery_info(struct imx_i2c_struct *i2c_imx,
> >>  {
> >>       struct i2c_bus_recovery_info *rinfo = &i2c_imx->rinfo;
> >>
> >> +     /* if pinctrl is not supported on the system */
> >> +     if (IS_ERR(i2c_imx->pinctrl))
> >> +             i2c_imx->pinctrl = NULL;
> >> +
> >> +     if (!i2c_imx->pinctrl) {
> >> +             dev_info(&pdev->dev, "can't get pinctrl, bus recovery not supported\n");
> >> +             return;
> >> +     }
> >> +
> >>       i2c_imx->pinctrl_pins_default = pinctrl_lookup_state(i2c_imx->pinctrl,
> >>                       PINCTRL_STATE_DEFAULT);
> >>       i2c_imx->pinctrl_pins_gpio = pinctrl_lookup_state(i2c_imx->pinctrl,
> >> @@ -1081,8 +1090,11 @@ static int i2c_imx_probe(struct platform_device *pdev)
> >>               return ret;
> >>       }
> >>
> >> +     /* optional bus recovery feature through pinctrl */
> >>       i2c_imx->pinctrl = devm_pinctrl_get(&pdev->dev);
> >> -     if (IS_ERR(i2c_imx->pinctrl)) {
> >> +     /* bailout on -ENOMEM or -EPROBE_DEFER, continue for other errors */
> >> +     if (PTR_ERR(i2c_imx->pinctrl) == -ENOMEM ||
> >> +                     PTR_ERR(i2c_imx->pinctrl) == -EPROBE_DEFER) {
> >>               ret = PTR_ERR(i2c_imx->pinctrl);
> >>               goto clk_disable;
> >>       }
> >
> > devm_pinctrl_get might return the following error-valued pointers:
> >  - -EINVAL
> >  - -ENOMEM
> >  - -ENODEV
> >  - -EPROBE_DEFER
> >
> > There are several error paths returning -EINVAL, one is when an invalid
> > phandle is used. Do you really want to ignore that?
> >
> > IMO error handling is better done with inverse logic, that is continue
> > on some explicit error, bail out on all unknown stuff. This tends to be
> > more robust. Also the comment should be improved to not explain that for
> > -ENOMEM and -EPROBE_DEFER we bail out (which should be obvious for
> > anyone who can read C) but to explain why.
> 
> What you said is true for normal error handling, but in this scenario
> it is intentional to ignore all pinctrl related errors except critical
> ones because failing to have pinctrl for an optional feature shouldn't
> impact the function of normal i2c.  We choose to catch -ENOMEM because
> the error could also cause problem for i2c probe, and -EPROBE_DEFER
> because it's possible that the pinctrl will be ready later and we want
> to give it a chance.  The i2c driver really don't care why the pinctrl
> was not usable.  I thought I added comment before the
> devm_pinctrl_get() to explain that the pinctrl is optional.  Hopefully
> you are not suggesting to explain what -ENOMEM and -EPROBE_DEFER mean
> in the comment. :)

You wrote

	/* optional bus recovery feature through pinctrl */

there. I'd expect to read something like:

	/*
	 * If pinctrl is available it might be possible to switch the
	 * SDA and SCL lines to their GPIO functions and do a recovery
	 * procedure in this mode. If there is anything wrong with
	 * pinctrl we cannot do this and simply skip it.
	 */
 
> > Also I'd put
> >
> >         i2c_imx->pinctrl = NULL;
> >
> > directly after devm_pinctrl_get() which I consider the more obvious
> > place for this.
> 
> On the other hand, put it together with the actually judgement can
> make it clear that it is catching both IS_ERR and NULL returns from
> devm_pinctrl_get()?

When you do it immediately, you have:

	if (i2c_imx->pinctrl)
		use_it();
	else
		ignore_it();

which looks clean. And if later another piece of code is added that
works on the pinctrl value, you don't have to care about the order (or
set it to NULL at two places). Instead you can consider the value const
in the complete driver apart from the little snippet that assigns to it
in .probe().

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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