netdev - Re: [PATCH V2 08/14] net: ks8851: Use 16-bit writes to program MAC address

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Date:   Fri, 27 Mar 2020 19:16:26 +0100
From:   Marek Vasut <marex@...x.de>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Lukas Wunner <lukas@...ner.de>, Petr Stetiar <ynezz@...e.cz>,
        YueHaibing <yuehaibing@...wei.com>
Subject: Re: [PATCH V2 08/14] net: ks8851: Use 16-bit writes to program MAC
 address

On 3/25/20 6:30 PM, Michal Kubecek wrote:
> On Wed, Mar 25, 2020 at 06:05:30PM +0100, Marek Vasut wrote:
>> On 3/25/20 5:56 PM, Michal Kubecek wrote:
>>> On Wed, Mar 25, 2020 at 04:05:37PM +0100, Marek Vasut wrote:
>>>> On the SPI variant of KS8851, the MAC address can be programmed with
>>>> either 8/16/32-bit writes. To make it easier to support the 16-bit
>>>> parallel option of KS8851 too, switch both the MAC address programming
>>>> and readout to 16-bit operations.
>>>>
>>>> Remove ks8851_wrreg8() as it is not used anywhere anymore.
>>>>
>>>> There should be no functional change.
>>>>
>>>> Signed-off-by: Marek Vasut <marex@...x.de>
>>>> Cc: David S. Miller <davem@...emloft.net>
>>>> Cc: Lukas Wunner <lukas@...ner.de>
>>>> Cc: Petr Stetiar <ynezz@...e.cz>
>>>> Cc: YueHaibing <yuehaibing@...wei.com>
>>>> ---
>>>> V2: Get rid of the KS_MAR(i + 1) by adjusting KS_MAR(x) macro
>>>> ---
>>> [...]
>>>> @@ -358,8 +329,12 @@ static int ks8851_write_mac_addr(struct net_device *dev)
>>>>  	 * the first write to the MAC address does not take effect.
>>>>  	 */
>>>>  	ks8851_set_powermode(ks, PMECR_PM_NORMAL);
>>>> -	for (i = 0; i < ETH_ALEN; i++)
>>>> -		ks8851_wrreg8(ks, KS_MAR(i), dev->dev_addr[i]);
>>>> +
>>>> +	for (i = 0; i < ETH_ALEN; i += 2) {
>>>> +		val = (dev->dev_addr[i] << 8) | dev->dev_addr[i + 1];
>>>> +		ks8851_wrreg16(ks, KS_MAR(i), val);
>>>> +	}
>>>> +
>>>>  	if (!netif_running(dev))
>>>>  		ks8851_set_powermode(ks, PMECR_PM_SOFTDOWN);
>>>>  
>>>> @@ -377,12 +352,16 @@ static int ks8851_write_mac_addr(struct net_device *dev)
>>>>  static void ks8851_read_mac_addr(struct net_device *dev)
>>>>  {
>>>>  	struct ks8851_net *ks = netdev_priv(dev);
>>>> +	u16 reg;
>>>>  	int i;
>>>>  
>>>>  	mutex_lock(&ks->lock);
>>>>  
>>>> -	for (i = 0; i < ETH_ALEN; i++)
>>>> -		dev->dev_addr[i] = ks8851_rdreg8(ks, KS_MAR(i));
>>>> +	for (i = 0; i < ETH_ALEN; i += 2) {
>>>> +		reg = ks8851_rdreg16(ks, KS_MAR(i));
>>>> +		dev->dev_addr[i] = reg & 0xff;
>>>> +		dev->dev_addr[i + 1] = reg >> 8;
>>>> +	}
>>>>  
>>>>  	mutex_unlock(&ks->lock);
>>>>  }
>>>
>>> It seems my question from v1 went unnoticed and the inconsistency still
>>> seems to be there so let me ask again: when writing, you put addr[i]
>>> into upper part of the 16-bit value and addr[i+1] into lower but when 
>>> reading, you do the opposite. Is it correct?
>>
>> I believe so, and it works at least on the hardware I have here.
>> I need to wait for Lukas to verify that on KS8851 SPI edition tomorrow
>> (that's also why I sent out the V2, so he can test it out)
> 
> That's a bit surprising (and counterintuitive) as it means that if you do
> 
>   ks8851_wrreg16(ks, a, val);
>   val = ks8851_rdreg16(ks, a);
> 
> you read a different value than you wrote. But I know nothing about the
> hardware (I only noticed the strange inconsistency) so I can't say where
> does it come from.

So this really does need fixing.