linux-kernel - Re: [PATCH v11 1/5] can: m_can: Create a m

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Message-ID: <35d179a7-2682-111e-638b-903559f0974a@ti.com>
Date:   Wed, 8 May 2019 14:54:56 -0500
From:   Dan Murphy <dmurphy@...com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>, <wg@...ndegger.com>,
        <davem@...emloft.net>
CC:     <linux-can@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 1/5] can: m_can: Create a m_can platform framework

Marc

Thanks for the comments

On 5/8/19 9:35 AM, Marc Kleine-Budde wrote:
> On 3/19/19 6:26 PM, Dan Murphy wrote:
>> Create a m_can platform framework that peripheral
>> devices can register to and use common code and register sets.
>> The peripheral devices may provide read/write and configuration
>> support of the IP.
>>
>> Acked-by: Wolfgang Grandegger <wg@...ndegger.com>
>> Signed-off-by: Dan Murphy <dmurphy@...com>
> 
> [...]
> 
>> -/* m_can private data structure */
>> -struct m_can_priv {
>> -	struct can_priv can;	/* must be the first member */
>> -	struct napi_struct napi;
>> -	struct net_device *dev;
>> -	struct device *device;
>> -	struct clk *hclk;
>> -	struct clk *cclk;
>> -	void __iomem *base;
>> -	u32 irqstatus;
>> -	int version;
>> -
>> -	/* message ram configuration */
>> -	void __iomem *mram_base;
>> -	struct mram_cfg mcfg[MRAM_CFG_NUM];
>> -};
>> +static u32 m_can_read(struct m_can_priv *priv, enum m_can_reg reg)
>> +{
>> +	if (priv->ops->read_reg)
>> +		return priv->ops->read_reg(priv, reg);
>> +	else
>> +		return -EINVAL;
>> +}
> 
> How do you plan to check the return value here?
> What's the difference between a register value of 0xffffffe9 and
> returning -EINVAL?
> 

Good point.  I could just inline this and return whatever is sent from the callback
and as you said allow a backtrace to happen if read_reg is invalid.

>>  
>> -static inline u32 m_can_read(const struct m_can_priv *priv, enum m_can_reg reg)
>> +static int m_can_write(struct m_can_priv *priv, enum m_can_reg reg, u32 val)
>>  {
>> -	return readl(priv->base + reg);
>> +	if (priv->ops->write_reg)
>> +		return priv->ops->write_reg(priv, reg, val);
>> +	else
>> +		return -EINVAL;
>>  }
> 
> I don't see anyone checking the return value. Better just dereference
> the pointer and the kernel will produce a nice backtrace.
> 
> Same should be done for all read and write variants.
> 

I will need to go through this and see if there is any caller checking the return.  But
I think you are correct.  If thats true I will just change this to a void, inline the function
and allow a backtrace if the callback is null

Dan



> Marc
>