[v3] i2c: designware: add reset interface

Some platforms like hi3660 need do reset first to allow accessing registers

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Ramiro Oliveira <ramiro.oliveira@synopsys.com>
---
 drivers/i2c/busses/i2c-designware-core.h    |  1 +
 drivers/i2c/busses/i2c-designware-platdrv.c | 28 ++++++++++++++++++++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

On Friday, December 23, 2016 9:40:51 PM CET Zhangfei Gao wrote:
> @@ -176,6 +177,14 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
>         dev->irq = irq;
>         platform_set_drvdata(pdev, dev);
>  
> +       dev->rst = devm_reset_control_get_optional_exclusive(&pdev->dev, NULL);
> +       if (IS_ERR(dev->rst)) {
> +               if (PTR_ERR(dev->rst) == -EPROBE_DEFER)
> +                       return -EPROBE_DEFER;
> +       } else {
> +               reset_control_deassert(dev->rst);
> +       }
> +

Sorry for the late reply, I only now stumbled over this. I think it's
generally wrong to ignore any error aside from -EPROBE_DEFER. It's
better to single-out the error conditions you want to ignore (e.g.
no reset specified) and ignore those but return an error for
all other problems.

> @@ -270,10 +280,18 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
>         }
>  
>         r = i2c_dw_probe(dev);
> -       if (r && !dev->pm_runtime_disabled)
> -               pm_runtime_disable(&pdev->dev);
> +       if (r)
> +               goto exit_probe;
>  
>         return r;
> +
> +exit_probe:
> +       if (!dev->pm_runtime_disabled)
> +               pm_runtime_disable(&pdev->dev);
> +exit_reset:
> +       if (!IS_ERR_OR_NULL(dev->rst))
> +               reset_control_assert(dev->rst);
> +       return r;
> 

try to avoid the IS_ERR_OR_NULL() check, it usually indicates either
a bad interface, or that the interface is used wrong.

In this case, I think we can't get here with a NULL dev->rst
pointer, so it's better to only check IS_ERR, or to explicitly
set the pointer to NULL in case there is no reset line.

	Arnd
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On Wed, 2017-01-04 at 15:55 +0100, Arnd Bergmann wrote:
> On Friday, December 23, 2016 9:40:51 PM CET Zhangfei Gao wrote:
> > @@ -176,6 +177,14 @@ static int dw_i2c_plat_probe(struct
> > platform_device *pdev)
> >         dev->irq = irq;
> >         platform_set_drvdata(pdev, dev);
> >  
> > +       dev->rst = devm_reset_control_get_optional_exclusive(&pdev-
> > >dev, NULL);
> > +       if (IS_ERR(dev->rst)) {
> > +               if (PTR_ERR(dev->rst) == -EPROBE_DEFER)
> > +                       return -EPROBE_DEFER;
> > +       } else {
> > +               reset_control_deassert(dev->rst);
> > +       }
> > +
> 
> Sorry for the late reply, I only now stumbled over this. I think it's
> generally wrong to ignore any error aside from -EPROBE_DEFER. It's
> better to single-out the error conditions you want to ignore (e.g.
> no reset specified) and ignore those but return an error for
> all other problems.

Which means that reset framework whenever work _optional is used should
return error iff (mind two f:s) there is a problem with existing
control.

> 
> > @@ -270,10 +280,18 @@ static int dw_i2c_plat_probe(struct
> > platform_device *pdev)
> >         }
> >  
> >         r = i2c_dw_probe(dev);
> > -       if (r && !dev->pm_runtime_disabled)
> > -               pm_runtime_disable(&pdev->dev);
> > +       if (r)
> > +               goto exit_probe;
> >  
> >         return r;
> > +
> > +exit_probe:
> > +       if (!dev->pm_runtime_disabled)
> > +               pm_runtime_disable(&pdev->dev);
> > +exit_reset:
> > +       if (!IS_ERR_OR_NULL(dev->rst))
> > +               reset_control_assert(dev->rst);
> > +       return r;
> > 
> 
> try to avoid the IS_ERR_OR_NULL() check, it usually indicates either
> a bad interface, or that the interface is used wrong.

Please, fix reset framework first than.

For my understanding:
It should return NULL for optional reset control.
It should not fail on NULL argument.


> In this case, I think we can't get here with a NULL dev->rst
> pointer, so it's better to only check IS_ERR, or to explicitly
> set the pointer to NULL in case there is no reset line.
> 
> 	Arnd

On Wednesday, January 4, 2017 5:35:19 PM CET Andy Shevchenko wrote:


> > > @@ -270,10 +280,18 @@ static int dw_i2c_plat_probe(struct
> > > platform_device *pdev)
> > >         }
> > >  
> > >         r = i2c_dw_probe(dev);
> > > -       if (r && !dev->pm_runtime_disabled)
> > > -               pm_runtime_disable(&pdev->dev);
> > > +       if (r)
> > > +               goto exit_probe;
> > >  
> > >         return r;
> > > +
> > > +exit_probe:
> > > +       if (!dev->pm_runtime_disabled)
> > > +               pm_runtime_disable(&pdev->dev);
> > > +exit_reset:
> > > +       if (!IS_ERR_OR_NULL(dev->rst))
> > > +               reset_control_assert(dev->rst);
> > > +       return r;
> > > 
> > 
> > try to avoid the IS_ERR_OR_NULL() check, it usually indicates either
> > a bad interface, or that the interface is used wrong.
> 
> Please, fix reset framework first than.
> 
> For my understanding:
> It should return NULL for optional reset control.
> It should not fail on NULL argument.

I think we discussed that a few times. Your suggestion makes sense
to me, but I don't know why we don't already do that, maybe there
is a good reason.

	Arnd
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