Re: [PATCH v5] i2c: imx: make bus recovery through pinctrl optional

On Tue, Sep 6, 2016 at 1:58 PM, Uwe Kleine-König
[off-list ref] wrote:

On Fri, Aug 19, 2016 at 05:05:22PM -0500, Li Yang wrote:

quoted

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 <redacted>
Cc: Gao Pan <redacted>
Cc: Uwe Kleine-König <redacted>
Acked-by: Linus Walleij <redacted>
---
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. :)

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()?

-- 
- Leo