linux-kernel - Re: [PATCH v8 03/22] counter: 104-quad-8: Return error when invalid mode during ceiling

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Date:   Sat, 20 Feb 2021 10:30:03 -0600
From:   David Lechner <david@...hnology.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>, jic23@...nel.org
Cc:     kernel@...gutronix.de, linux-stm32@...md-mailman.stormreply.com,
        a.fatoum@...gutronix.de, kamel.bouhara@...tlin.com,
        gwendal@...omium.org, alexandre.belloni@...tlin.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
Subject: Re: [PATCH v8 03/22] counter: 104-quad-8: Return error when invalid
 mode during ceiling_write

On 2/12/21 6:13 AM, William Breathitt Gray wrote:
> The 104-QUAD-8 only has two count modes where a ceiling value makes
> sense: Range Limit and Modulo-N. Outside of these two modes, setting a
> ceiling value is an invalid operation -- so let's report it as such by
> returning -EINVAL.
> 
> Fixes: fc069262261c ("counter: 104-quad-8: Add lock guards - generic interface")
> Cc: Syed Nayyar Waris <syednwaris@...il.com>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
> ---
>   drivers/counter/104-quad-8.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
> index 9691f8612be8..f0608b21196a 100644
> --- a/drivers/counter/104-quad-8.c
> +++ b/drivers/counter/104-quad-8.c
> @@ -714,13 +714,14 @@ static ssize_t quad8_count_ceiling_write(struct counter_device *counter,
>   	switch (priv->count_mode[count->id]) {
>   	case 1:
>   	case 3:
> +		mutex_unlock(&priv->lock);
>   		quad8_preset_register_set(priv, count->id, ceiling);
> -		break;
> +		return len;
>   	}
>   
>   	mutex_unlock(&priv->lock);
>   
> -	return len;
> +	return -EINVAL;
>   }
>   
>   static ssize_t quad8_count_preset_enable_read(struct counter_device *counter,
> 

What happens if the register is written to when in the wrong mode?

If it doesn't hurt anything, I would suggest always writing the register
instead so that users don't have to know worry about the fact that the mode
has to be set first.