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

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Date:   Wed, 25 Mar 2020 18:30:08 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Marek Vasut <marex@...x.de>
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 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.

Michal Kubecek