linux-kernel - Re: [PATCH v11 18/33] counter: Return error code on invalid modes

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Message-ID: <YOA+456Ns2PKdKa8@shinobu>
Date:   Sat, 3 Jul 2021 19:41:39 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     linux-stm32@...md-mailman.stormreply.com, kernel@...gutronix.de,
        a.fatoum@...gutronix.de, kamel.bouhara@...tlin.com,
        gwendal@...omium.org, alexandre.belloni@...tlin.com,
        david@...hnology.com, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        syednwaris@...il.com, patrick.havelange@...ensium.com,
        fabrice.gasnier@...com, mcoquelin.stm32@...il.com,
        alexandre.torgue@...com, o.rempel@...gutronix.de,
        jarkko.nikula@...ux.intel.com,
        Fabrice Gasnier <fabrice.gasnier@...s.st.com>
Subject: Re: [PATCH v11 18/33] counter: Return error code on invalid modes

On Wed, Jun 09, 2021 at 04:47:31PM +0100, Jonathan Cameron wrote:
> On Wed,  9 Jun 2021 10:31:21 +0900
> William Breathitt Gray <vilhelm.gray@...il.com> wrote:
> > diff --git a/drivers/counter/stm32-lptimer-cnt.c b/drivers/counter/stm32-lptimer-cnt.c
> > index c19d998df5ba..78f383b77bd2 100644
> > --- a/drivers/counter/stm32-lptimer-cnt.c
> > +++ b/drivers/counter/stm32-lptimer-cnt.c
> > @@ -206,9 +206,10 @@ static int stm32_lptim_cnt_function_set(struct counter_device *counter,
> >  		priv->quadrature_mode = 1;
> >  		priv->polarity = STM32_LPTIM_SYNAPSE_ACTION_BOTH_EDGES;
> >  		return 0;
> > +	default:
> > +		/* should never reach this path */
> > +		return -EINVAL;
> 
> In this particular case we are already exhaustive.  So we should have neither default
> nor ideally the return below.  
> 
> If we have a local variable of the relevant enum type, then I think the compiler
> should be able to tell this is exhaustive and usefully it will then issue
> a warning should the enum gain more entries in future.

I tried using a local variable of type enum stm32_lptim_cnt_function,
but unfortunately the compiler is not able to tell this is exhaustive --
I think it's because 'function' is of type enum counter_function which
can theoretically have a value outside enum stm32_lptim_cnt_function.

> 
> >  	}
> > -
> > -	return -EINVAL;
> >  }
> >  
> >  static ssize_t stm32_lptim_cnt_enable_read(struct counter_device *counter,
> > @@ -326,9 +327,10 @@ static int stm32_lptim_cnt_action_get(struct counter_device *counter,
> >  	case STM32_LPTIM_ENCODER_BOTH_EDGE:
> >  		*action = priv->polarity;
> >  		return 0;
> > +	default:
> 
> Same in this path.
> 
> > +		/* should never reach this path */
> > +		return -EINVAL;
> >  	}
> > -
> > -	return -EINVAL;
> >  }
> >  
> >  static int stm32_lptim_cnt_action_set(struct counter_device *counter,
> > diff --git a/drivers/counter/ti-eqep.c b/drivers/counter/ti-eqep.c
> > index 65df9ef5b5bc..878725c2f010 100644
> > --- a/drivers/counter/ti-eqep.c
> > +++ b/drivers/counter/ti-eqep.c
> > @@ -157,44 +157,39 @@ static int ti_eqep_action_get(struct counter_device *counter,
> >  		 * QEPA and QEPB trigger QCLK.
> >  		 */
> >  		*action = TI_EQEP_SYNAPSE_ACTION_BOTH_EDGES;
> > -		break;
> > +		return 0;
> >  	case TI_EQEP_COUNT_FUNC_DIR_COUNT:
> >  		/* In direction-count mode only rising edge of QEPA is counted
> >  		 * and QEPB gives direction.
> >  		 */
> > -		switch (synapse->signal->id) {
> I'd rather see this as
> 
> case TI_EQEP_SIGNAL_QEPA:
> caes TI_EQEP_SIGNAL_QEPB:
> 
> To make it clear what the two cases are.  Then we don't need the default
> assuming the type is right so the compiler should be able to see
> that we have been exhaustive.

I can refactor this back to a switch statement as you suggest, but we'll
need the default case for the same reason as mentioned above.

William Breathitt Gray

> 
> > -		case TI_EQEP_SIGNAL_QEPA:
> > -			*action = TI_EQEP_SYNAPSE_ACTION_RISING_EDGE;
> > -			break;
> > -		default:
> > +		if (synapse->signal->id == TI_EQEP_SIGNAL_QEPB)
> >  			*action = TI_EQEP_SYNAPSE_ACTION_NONE;
> > -			break;
> > -		}
> > -		break;
> > +		else
> > +			*action = TI_EQEP_SYNAPSE_ACTION_RISING_EDGE;
> > +		return 0;
> >  	case TI_EQEP_COUNT_FUNC_UP_COUNT:
> >  	case TI_EQEP_COUNT_FUNC_DOWN_COUNT:
> >  		/* In up/down-count modes only QEPA is counted and QEPB is not
> >  		 * used.
> >  		 */
> > -		switch (synapse->signal->id) {
> > -		case TI_EQEP_SIGNAL_QEPA:
> > -			err = regmap_read(priv->regmap16, QDECCTL, &qdecctl);
> > -			if (err)
> > -				return err;
> > -
> > -			if (qdecctl & QDECCTL_XCR)
> > -				*action = TI_EQEP_SYNAPSE_ACTION_BOTH_EDGES;
> > -			else
> > -				*action = TI_EQEP_SYNAPSE_ACTION_RISING_EDGE;
> > -			break;
> > -		default:
> > +		if (synapse->signal->id == TI_EQEP_SIGNAL_QEPB) {
> >  			*action = TI_EQEP_SYNAPSE_ACTION_NONE;
> 
> Same as above
> 
> > -			break;
> > +			return 0;
> >  		}
> > -		break;
> > -	}
> >  
> > -	return 0;
> > +		err = regmap_read(priv->regmap16, QDECCTL, &qdecctl);
> > +		if (err)
> > +			return err;
> > +
> > +		if (qdecctl & QDECCTL_XCR)
> > +			*action = TI_EQEP_SYNAPSE_ACTION_BOTH_EDGES;
> > +		else
> > +			*action = TI_EQEP_SYNAPSE_ACTION_RISING_EDGE;
> > +		return 0;
> > +	default:
> > +		/* should never reach this path */
> > +		return -EINVAL;
> > +	}
> >  }
> >  
> >  static const struct counter_ops ti_eqep_counter_ops = {
> 

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