Re: [PATCH 07/14] net: ks8851: Use 16-bit writes to program MAC address
From: Lukas Wunner <lukas@wunner.de>
Date: 2020-03-24 08:13:15
On Tue, Mar 24, 2020 at 12:42:56AM +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.
[...]
quoted hunk ↗ jump to hunk
static int ks8851_write_mac_addr(struct net_device *dev) { struct ks8851_net *ks = netdev_priv(dev); + u16 val; int i; mutex_lock(&ks->lock);@@ -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 + 1), val); + } +
This looks like it won't work on little-endian machines: The MAC bytes
are stored in dev->dev_addr as 012345, but in the EEPROM they're stored
as 543210. The first 16-bit value that you write is 10 on big-endian
and 01 on little-endian if I'm not mistaken.
By only writing 8-bit values, the original author elegantly sidestepped
this issue.
Maybe the simplest and most readable solution is something like:
u8 val[2];
...
val[0] = dev->dev_addr[i+1];
val[1] = dev->dev_addr;
Then cast val to a u16 when passing it to ks8851_wrreg16().
Alternatively, use cpu_to_be16().
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 + 1));
+ dev->dev_addr[i] = reg & 0xff;
+ dev->dev_addr[i + 1] = reg >> 8;
+ }Same here. These seem to be the only two places where KS_MAR() is used. You may want to adjust that macro so that you don't have to add 1 in each of the two places. Thanks, Lukas