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[PATCH v2 13/14] usb: host: ehci-st: simplify optional reset handling

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  [PATCH v2 13/14] usb: host: ehci-st: simplify optional reset handling Philipp Zabel <p.zabel@pengutronix.de> - 2017-03-15 12:40 +0100
    Re: [PATCH v2 13/14] usb: host: ehci-st: simplify optional reset  handling Alan Stern <stern@rowland.harvard.edu> - 2017-03-15 15:40 +0100
      Re: [PATCH v2 13/14] usb: host: ehci-st: simplify optional reset  handling Philipp Zabel <p.zabel@pengutronix.de> - 2017-03-15 16:30 +0100

#1601321 — [PATCH v2 13/14] usb: host: ehci-st: simplify optional reset handling

As of commit bb475230b8e5 ("reset: make optional functions really
optional"), the reset framework API calls use NULL pointers to describe
optional, non-present reset controls.

This allows to return errors from devm_reset_control_get_optional_shared
unconditionally.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
---
 drivers/usb/host/ehci-st.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/host/ehci-st.c b/drivers/usb/host/ehci-st.c
index be4a2788fc582..12e803d2c98df 100644
--- a/drivers/usb/host/ehci-st.c
+++ b/drivers/usb/host/ehci-st.c
@@ -210,18 +210,14 @@ static int st_ehci_platform_probe(struct platform_device *dev)
 		devm_reset_control_get_optional_shared(&dev->dev, "power");
 	if (IS_ERR(priv->pwr)) {
 		err = PTR_ERR(priv->pwr);
-		if (err == -EPROBE_DEFER)
-			goto err_put_clks;
-		priv->pwr = NULL;
+		goto err_put_clks;
 	}
 
 	priv->rst =
 		devm_reset_control_get_optional_shared(&dev->dev, "softreset");
 	if (IS_ERR(priv->rst)) {
 		err = PTR_ERR(priv->rst);
-		if (err == -EPROBE_DEFER)
-			goto err_put_clks;
-		priv->rst = NULL;
+		goto err_put_clks;
 	}
 
 	if (pdata->power_on) {
-- 
2.11.0

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#1601445 — Re: [PATCH v2 13/14] usb: host: ehci-st: simplify optional reset handling

On Wed, 15 Mar 2017, Philipp Zabel wrote:

> As of commit bb475230b8e5 ("reset: make optional functions really
> optional"), the reset framework API calls use NULL pointers to describe
> optional, non-present reset controls.

What does it use to describe genuine errors?

> This allows to return errors from devm_reset_control_get_optional_shared
> unconditionally.
> 
> Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> ---
>  drivers/usb/host/ehci-st.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/usb/host/ehci-st.c b/drivers/usb/host/ehci-st.c
> index be4a2788fc582..12e803d2c98df 100644
> --- a/drivers/usb/host/ehci-st.c
> +++ b/drivers/usb/host/ehci-st.c
> @@ -210,18 +210,14 @@ static int st_ehci_platform_probe(struct platform_device *dev)
>  		devm_reset_control_get_optional_shared(&dev->dev, "power");
>  	if (IS_ERR(priv->pwr)) {
>  		err = PTR_ERR(priv->pwr);
> -		if (err == -EPROBE_DEFER)
> -			goto err_put_clks;
> -		priv->pwr = NULL;
> +		goto err_put_clks;
>  	}
>  
>  	priv->rst =
>  		devm_reset_control_get_optional_shared(&dev->dev, "softreset");
>  	if (IS_ERR(priv->rst)) {
>  		err = PTR_ERR(priv->rst);
> -		if (err == -EPROBE_DEFER)
> -			goto err_put_clks;
> -		priv->rst = NULL;
> +		goto err_put_clks;
>  	}
>  
>  	if (pdata->power_on) {

These changes do not agree with the patch description.  If any sort of 
error besides EPROBE_DEFER occurs then:

	the old code sets priv->pwr or priv->rst to NULL and continues;

	the new code returns with an error.

The only way the patch could be equivalent to the existing code would
be if devm_reset_control_get_optional_shared() returns no errors other
than EPROBE_DEFER.  But the patch description doesn't say this.

Alan Stern

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#1601485 — Re: [PATCH v2 13/14] usb: host: ehci-st: simplify optional reset handling

Hi Alan,

On Wed, 2017-03-15 at 10:35 -0400, Alan Stern wrote:
> On Wed, 15 Mar 2017, Philipp Zabel wrote:
> 
> > As of commit bb475230b8e5 ("reset: make optional functions really
> > optional"), the reset framework API calls use NULL pointers to describe
> > optional, non-present reset controls.
> 
> What does it use to describe genuine errors?

Negative error pointers, as before. The only difference is that instead
of returning -ENOENT if no resets are specified in the device tree, the
optional reset_control_get variants now return NULL.

> > This allows to return errors from devm_reset_control_get_optional_shared
> > unconditionally.
> > 
> > Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> > ---
> >  drivers/usb/host/ehci-st.c | 8 ++------
> >  1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/usb/host/ehci-st.c b/drivers/usb/host/ehci-st.c
> > index be4a2788fc582..12e803d2c98df 100644
> > --- a/drivers/usb/host/ehci-st.c
> > +++ b/drivers/usb/host/ehci-st.c
> > @@ -210,18 +210,14 @@ static int st_ehci_platform_probe(struct platform_device *dev)
> >  		devm_reset_control_get_optional_shared(&dev->dev, "power");
> >  	if (IS_ERR(priv->pwr)) {
> >  		err = PTR_ERR(priv->pwr);
> > -		if (err == -EPROBE_DEFER)
> > -			goto err_put_clks;
> > -		priv->pwr = NULL;
> > +		goto err_put_clks;
> >  	}
> >  
> >  	priv->rst =
> >  		devm_reset_control_get_optional_shared(&dev->dev, "softreset");
> >  	if (IS_ERR(priv->rst)) {
> >  		err = PTR_ERR(priv->rst);
> > -		if (err == -EPROBE_DEFER)
> > -			goto err_put_clks;
> > -		priv->rst = NULL;
> > +		goto err_put_clks;
> >  	}
> >  
> >  	if (pdata->power_on) {
> 
> These changes do not agree with the patch description.  If any sort of 
> error besides EPROBE_DEFER occurs then:
>
> 	the old code sets priv->pwr or priv->rst to NULL and continues;
> 
> 	the new code returns with an error.
> 
> The only way the patch could be equivalent to the existing code would
> be if devm_reset_control_get_optional_shared() returns no errors other
> than EPROBE_DEFER.  But the patch description doesn't say this.
> 
> Alan Stern

You are right, devm_reset_control_get_optional_shared can return:

-ENOMEM, returned by devres_alloc in __devm_reset_control_get,

-EILSEQ, returned by of_property_match_string in __of_reset_control_get
if the "reset-names" DT property is broken,

-EINVAL, returned by of_parse_phandle_with_args in
__of_reset_control_get, if there is a reset phandle specified in the
device tree but it is pointing to an invalid reset controller node
(missing "#reset-cells" property or number of phandle arguments does not
match).

-EINVAL, returned by the reset controller driver's choice of of_xlate,
also if the reset is specified but somehow invalid.

So yes, if there was a genuine error in the device tree, we would now
return the error instead of silently ignoring it as before. I assume
that these errors were never intended to be ignored, it just happened to
be a hassle to separate them from the -ENOENT condition with the old
API.

regards
Philipp

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