>> +    do {
>> +            /* IPG_PC_MGMTDATA is a power of 2; compiler knows to shift */
>> +            u8 d = ((data >> --len) & 1) * IPG_PC_MGMTDATA;
>> +            /* + rather than | lets compiler microoptimize better */
>> +            ipg_drive_phy_ctl_low_high(ioaddr, d + otherbits);
>> +    } while (len);

> Imho something is not quite right when the code needs a comment every line
> and I am mildly convinced that we really want to honk an "optimizing mdio
> methods is ok" signal around.

Oh, but those are SPACE-saving optimiztions. :-)
I know it's not time-critical; it's really pure hack value, but is it
that evil?

> "while (len--) {" is probably more akpm-ish btw.

Well spotted.

[...]
>>  static int mdio_read(struct net_device * dev, int phy_id, int phy_reg)
>>  {
>>      void __iomem *ioaddr = ipg_ioaddr(dev);
>> +    u8 const polarity = ipg_r8(PHY_CTRL) &
>> +                    (IPG_PC_DUPLEX_POLARITY | IPG_PC_LINK_POLARITY);

> (IPG_PC_DUPLEX_POLARITY | IPG_PC_LINK_POLARITY) appears twice. I would not
> mind a #define for it.

I'm hardly going to go to war over over the matter, but actually I disagree.

There's a non-zero mental cost to keeping track of an additional name,
and when it's only used two times, and is pretty simple, I think reducing
the number of layers of #defines to understand is a positive advantage.
The above reads "the two polarity bits from the PHY_CTRL register"
to a person who's never read ipg.h.  Adding IPG_PC_POLARITY_BITS just
requires mentally dereferencing another layer of pointers.

Think of it as a function small enough that it can be inlined.

>> @@ -221,75 +240,30 @@ static int mdio_read(struct net_device * dev, int 
>> phy_id, int phy_reg)
>[...]
>> -    for (i = 0; i < p[6].len; i++) {
>> -            p[6].field |=
>> -                (read_phy_bit(ioaddr, polarity) << (p[6].len - 1 - i));
>> -    }
>> +    send_three_state(ioaddr, polarity);     /* TA first bit */
>> +    (void)read_phy_bit(ioaddr, polarity);           /* TA second bit */
>> +
>> +    for (i = 0; i < 16; i++)
>> +            data += data + read_phy_bit(ioaddr, polarity);
                ^^^^^^^^^^^^
> Huh ?

Okay, I guess you prefer
+               data = 2*data + read_phy_bit(ioaddr, polarity);

That's only one character longer and easier to understand.
Or even four characters:
+               data = (data<<1) + read_phy_bit(ioaddr, polarity);

That's just the synonym that happened to come out of my fingers at the
time.  There's no particular meaning to it.

>> @@ -299,11 +273,13 @@ static int mdio_read(struct net_device * dev, int 
>> phy_id, int phy_reg)
>>  static void mdio_write(struct net_device *dev, int phy_id, int phy_reg, int 
>> val)
[...]
>> +    mdio_write_bits(ioaddr, polarity, GMII_PREAMBLE, 32);
>> +    mdio_write_bits(ioaddr, polarity, GMII_ST << 14 | GMII_WRITE << 12 |
>> +                                      phy_id << 7 | phy_reg << 2 |
>> +                                      0x2, 16);

> Use the 80 cols luke:
>                                         phy_id << 7 | phy_reg << 2 | 0x2, 16);

Good spotting, thanks.

Here's a revised patch:

    drivers/net/ipg.c: Fixed style problems that AKPM noticed.
    
    (And a few more while at it.  Including an actual bug in enabling multicast
    due to & vs. && confusion.)

diff --git a/drivers/net/ipg.c b/drivers/net/ipg.c
index 3860fcd..fb69374 100644
--- a/drivers/net/ipg.c
+++ b/drivers/net/ipg.c
@@ -188,9 +188,9 @@ static void send_end(void __iomem *ioaddr, u8 
phyctrlpolarity)
                phyctrlpolarity) & IPG_PC_RSVD_MASK, PHY_CTRL);
 }
 
-static u16 read_phy_bit(void __iomem * ioaddr, u8 phyctrlpolarity)
+static unsigned read_phy_bit(void __iomem * ioaddr, u8 phyctrlpolarity)
 {
-       u16 bit_data;
+       unsigned bit_data;
 
        ipg_write_phy_ctl(ioaddr, IPG_PC_MGMTCLK_LO | phyctrlpolarity);
 
@@ -202,12 +202,31 @@ static u16 read_phy_bit(void __iomem * ioaddr, u8 
phyctrlpolarity)
 }
 
 /*
+ * Transmit the given bits, MSB-first, through the MgmtData bit (bit 1)
+ * of the PhyCtrl register. 1 <= len <= 32.  "ioaddr" is the register
+ * address, and "otherbits" are the values of the other bits.
+ */
+static void mdio_write_bits(void __iomem *ioaddr, u8 otherbits, u32 data, 
unsigned len)
+{
+       otherbits |= IPG_PC_MGMTDIR;
+       while (len--) {
+               /* IPG_PC_MGMTDATA is a power of 2; compiler knows to shift */
+               u8 d = ((data >> len) & 1) * IPG_PC_MGMTDATA;
+               /* + rather than | allows slight code size microoptimization */
+               ipg_drive_phy_ctl_low_high(ioaddr, d + otherbits);
+       }
+}
+
+/*
  * Read a register from the Physical Layer device located
  * on the IPG NIC, using the IPG PHYCTRL register.
  */
 static int mdio_read(struct net_device * dev, int phy_id, int phy_reg)
 {
        void __iomem *ioaddr = ipg_ioaddr(dev);
+       u8 const polarity = ipg_r8(PHY_CTRL) &
+                       (IPG_PC_DUPLEX_POLARITY | IPG_PC_LINK_POLARITY);
+       unsigned i, data = 0;
        /*
         * The GMII mangement frame structure for a read is as follows:
         *
@@ -218,78 +237,34 @@ static int mdio_read(struct net_device * dev, int phy_id, 
int phy_reg)
         * A = bit of Physical Layer device address (MSB first)
         * R = bit of register address (MSB first)
         * z = High impedance state
-        * D = bit of read data (MSB first)
+        * 0 = preamble bit sent by PHY
+        * D = bit of read data (MSB first), sent by PHY
         *
         * Transmission order is 'Preamble' field first, bits transmitted
-        * left to right (first to last).
+        * left to right (msbit-first).
         */
-       struct {
-               u32 field;
-               unsigned int len;
-       } p[] = {
-               { GMII_PREAMBLE,        32 },   /* Preamble */
-               { GMII_ST,              2  },   /* ST */
-               { GMII_READ,            2  },   /* OP */
-               { phy_id,               5  },   /* PHYAD */
-               { phy_reg,              5  },   /* REGAD */
-               { 0x0000,               2  },   /* TA */
-               { 0x0000,               16 },   /* DATA */
-               { 0x0000,               1  }    /* IDLE */
-       };
-       unsigned int i, j;
-       u8 polarity, data;
-
-       polarity  = ipg_r8(PHY_CTRL);
-       polarity &= (IPG_PC_DUPLEX_POLARITY | IPG_PC_LINK_POLARITY);
-
-       /* Create the Preamble, ST, OP, PHYAD, and REGAD field. */
-       for (j = 0; j < 5; j++) {
-               for (i = 0; i < p[j].len; i++) {
-                       /* For each variable length field, the MSB must be
-                        * transmitted first. Rotate through the field bits,
-                        * starting with the MSB, and move each bit into the
-                        * the 1st (2^1) bit position (this is the bit position
-                        * corresponding to the MgmtData bit of the PhyCtrl
-                        * register for the IPG).
-                        *
-                        * Example: ST = 01;
-                        *
-                        *          First write a '0' to bit 1 of the PhyCtrl
-                        *          register, then write a '1' to bit 1 of the
-                        *          PhyCtrl register.
-                        *
-                        * To do this, right shift the MSB of ST by the value:
-                        * [field length - 1 - #ST bits already written]
-                        * then left shift this result by 1.
-                        */
-                       data  = (p[j].field >> (p[j].len - 1 - i)) << 1;
-                       data &= IPG_PC_MGMTDATA;
-                       data |= polarity | IPG_PC_MGMTDIR;
-
-                       ipg_drive_phy_ctl_low_high(ioaddr, data);
-               }
-       }
-
-       send_three_state(ioaddr, polarity);
-
-       read_phy_bit(ioaddr, polarity);
+       mdio_write_bits(ioaddr, polarity, GMII_PREAMBLE, 32);
+       mdio_write_bits(ioaddr, polarity, GMII_ST<<12 | GMII_READ << 10 |
+                                         phy_id << 5 | phy_reg, 14);
 
        /*
         * For a read cycle, the bits for the next two fields (TA and
         * DATA) are driven by the PHY (the IPG reads these bits).
         */
-       for (i = 0; i < p[6].len; i++) {
-               p[6].field |=
-                   (read_phy_bit(ioaddr, polarity) << (p[6].len - 1 - i));
-       }
+       send_three_state(ioaddr, polarity);     /* TA first bit */
+       (void)read_phy_bit(ioaddr, polarity);           /* TA second bit */
+
+       for (i = 0; i < 16; i++)
+               data = 2*data + read_phy_bit(ioaddr, polarity);
 
+       /* Trailing idle */
        send_three_state(ioaddr, polarity);
        send_three_state(ioaddr, polarity);
        send_three_state(ioaddr, polarity);
        send_end(ioaddr, polarity);
 
        /* Return the value of the DATA field. */
-       return p[6].field;
+       return data;
 }
 
 /*
@@ -299,11 +274,13 @@ static int mdio_read(struct net_device * dev, int phy_id, 
int phy_reg)
 static void mdio_write(struct net_device *dev, int phy_id, int phy_reg, int 
val)
 {
        void __iomem *ioaddr = ipg_ioaddr(dev);
+       u8 const polarity = ipg_r8(PHY_CTRL) &
+                       (IPG_PC_DUPLEX_POLARITY | IPG_PC_LINK_POLARITY);
        /*
-        * The GMII mangement frame structure for a read is as follows:
+        * The GMII mangement frame structure for a write is as follows:
         *
         * |Preamble|st|op|phyad|regad|ta|      data      |idle|
-        * |< 32 1s>|01|10|AAAAA|RRRRR|z0|DDDDDDDDDDDDDDDD|z   |
+        * |< 32 1s>|01|01|AAAAA|RRRRR|10|DDDDDDDDDDDDDDDD|z   |
         *
         * <32 1s> = 32 consecutive logic 1 values
         * A = bit of Physical Layer device address (MSB first)
@@ -312,66 +289,17 @@ static void mdio_write(struct net_device *dev, int 
phy_id, int phy_reg, int val)
         * D = bit of write data (MSB first)
         *
         * Transmission order is 'Preamble' field first, bits transmitted
-        * left to right (first to last).
+        * left to right (msbit-first).
         */
-       struct {
-               u32 field;
-               unsigned int len;
-       } p[] = {
-               { GMII_PREAMBLE,        32 },   /* Preamble */
-               { GMII_ST,              2  },   /* ST */
-               { GMII_WRITE,           2  },   /* OP */
-               { phy_id,               5  },   /* PHYAD */
-               { phy_reg,              5  },   /* REGAD */
-               { 0x0002,               2  },   /* TA */
-               { val & 0xffff,         16 },   /* DATA */
-               { 0x0000,               1  }    /* IDLE */
-       };
-       unsigned int i, j;
-       u8 polarity, data;
-
-       polarity  = ipg_r8(PHY_CTRL);
-       polarity &= (IPG_PC_DUPLEX_POLARITY | IPG_PC_LINK_POLARITY);
-
-       /* Create the Preamble, ST, OP, PHYAD, and REGAD field. */
-       for (j = 0; j < 7; j++) {
-               for (i = 0; i < p[j].len; i++) {
-                       /* For each variable length field, the MSB must be
-                        * transmitted first. Rotate through the field bits,
-                        * starting with the MSB, and move each bit into the
-                        * the 1st (2^1) bit position (this is the bit position
-                        * corresponding to the MgmtData bit of the PhyCtrl
-                        * register for the IPG).
-                        *
-                        * Example: ST = 01;
-                        *
-                        *          First write a '0' to bit 1 of the PhyCtrl
-                        *          register, then write a '1' to bit 1 of the
-                        *          PhyCtrl register.
-                        *
-                        * To do this, right shift the MSB of ST by the value:
-                        * [field length - 1 - #ST bits already written]
-                        * then left shift this result by 1.
-                        */
-                       data  = (p[j].field >> (p[j].len - 1 - i)) << 1;
-                       data &= IPG_PC_MGMTDATA;
-                       data |= polarity | IPG_PC_MGMTDIR;
-
-                       ipg_drive_phy_ctl_low_high(ioaddr, data);
-               }
-       }
+       mdio_write_bits(ioaddr, polarity, GMII_PREAMBLE, 32);
+       mdio_write_bits(ioaddr, polarity, GMII_ST << 14 | GMII_WRITE << 12 |
+                                         phy_id << 7 | phy_reg << 2 | 0x2, 16);
+       mdio_write_bits(ioaddr, polarity, val, 16);     /* DATA */
 
        /* The last cycle is a tri-state, so read from the PHY. */
-       for (j = 7; j < 8; j++) {
-               for (i = 0; i < p[j].len; i++) {
-                       ipg_write_phy_ctl(ioaddr, IPG_PC_MGMTCLK_LO | polarity);
-
-                       p[j].field |= ((ipg_r8(PHY_CTRL) &
-                               IPG_PC_MGMTDATA) >> 1) << (p[j].len - 1 - i);
-
-                       ipg_write_phy_ctl(ioaddr, IPG_PC_MGMTCLK_HI | polarity);
-               }
-       }
+       ipg_write_phy_ctl(ioaddr, IPG_PC_MGMTCLK_LO | polarity);
+       (void)ipg_r8(PHY_CTRL);
+       ipg_write_phy_ctl(ioaddr, IPG_PC_MGMTCLK_HI | polarity);
 }
 
 /* Set LED_Mode JES20040127EEPROM */
@@ -379,18 +307,17 @@ static void ipg_set_led_mode(struct net_device *dev)
 {
        struct ipg_nic_private *sp = netdev_priv(dev);
        void __iomem *ioaddr = sp->ioaddr;
-       u32 mode;
+       u32 mode = ipg_r32(ASIC_CTRL);
 
-       mode = ipg_r32(ASIC_CTRL);
        mode &= ~(IPG_AC_LED_MODE_BIT_1 | IPG_AC_LED_MODE | IPG_AC_LED_SPEED);
 
-       if ((sp->LED_Mode & 0x03) > 1)
-               mode |= IPG_AC_LED_MODE_BIT_1;  /* Write Asic Control Bit 29 */
-
-       if ((sp->LED_Mode & 0x01) == 1)
+       if (sp->LED_Mode & 0x01)
                mode |= IPG_AC_LED_MODE;        /* Write Asic Control Bit 14 */
 
-       if ((sp->LED_Mode & 0x08) == 8)
+       if (sp->LED_Mode & 0x02)
+               mode |= IPG_AC_LED_MODE_BIT_1;  /* Write Asic Control Bit 29 */
+
+       if (sp->LED_Mode & 0x08)
                mode |= IPG_AC_LED_SPEED;       /* Write Asic Control Bit 27 */
 
        ipg_w32(mode, ASIC_CTRL);
@@ -401,11 +328,13 @@ static void ipg_set_phy_set(struct net_device *dev)
 {
        struct ipg_nic_private *sp = netdev_priv(dev);
        void __iomem *ioaddr = sp->ioaddr;
-       int physet;
+       u8 physet = ipg_r8(PHY_SET);
+       u8 newset = sp->LED_Mode >> 4;
 
-       physet = ipg_r8(PHY_SET);
-       physet &= ~(IPG_PS_MEM_LENB9B | IPG_PS_MEM_LEN9 | IPG_PS_NON_COMPDET);
-       physet |= ((sp->LED_Mode & 0x70) >> 4);
+       /* Change three bits of physet to values in newset */
+       newset ^= physet;
+       newset &= (IPG_PS_MEM_LENB9B | IPG_PS_MEM_LEN9 | IPG_PS_NON_COMPDET);
+       physet ^= newset;
        ipg_w8(physet, PHY_SET);
 }
 
@@ -444,7 +373,7 @@ static int ipg_find_phyaddr(struct net_device *dev)
        unsigned int phyaddr, i;
 
        for (i = 0; i < 32; i++) {
-               u32 status;
+               unsigned status;
 
                /* Search for the correct PHY address among 32 possible. */
                phyaddr = (IPG_NIC_PHY_ADDRESS + i) % 32;
@@ -470,10 +399,7 @@ static int ipg_config_autoneg(struct net_device *dev)
 {
        struct ipg_nic_private *sp = netdev_priv(dev);
        void __iomem *ioaddr = sp->ioaddr;
-       unsigned int txflowcontrol;
-       unsigned int rxflowcontrol;
-       unsigned int fullduplex;
-       unsigned int gig;
+       bool txflowcontrol, rxflowcontrol, fullduplex, gig;
        u32 mac_ctrl_val;
        u32 asicctrl;
        u8 phyctrl;
@@ -487,10 +413,10 @@ static int ipg_config_autoneg(struct net_device *dev)
        /* Set flags for use in resolving auto-negotation, assuming
         * non-1000Mbps, half duplex, no flow control.
         */
-       fullduplex = 0;
-       txflowcontrol = 0;
-       rxflowcontrol = 0;
-       gig = 0;
+       fullduplex = false;
+       txflowcontrol = false;
+       rxflowcontrol = false;
+       gig = false;
 
        /* To accomodate a problem in 10Mbps operation,
         * set a global flag if PHY running in 10Mbps mode.
@@ -512,7 +438,7 @@ static int ipg_config_autoneg(struct net_device *dev)
                break;
        case IPG_PC_LINK_SPEED_1000MBPS:
                printk("1000Mbps.\n");
-               gig = 1;
+               gig = true;
                break;
        default:
                printk("undefined!\n");
@@ -520,19 +446,20 @@ static int ipg_config_autoneg(struct net_device *dev)
        }
 
        if (phyctrl & IPG_PC_DUPLEX_STATUS) {
-               fullduplex = 1;
-               txflowcontrol = 1;
-               rxflowcontrol = 1;
+               fullduplex = true;
+               txflowcontrol = true;
+               rxflowcontrol = true;
        }
 
        /* Configure full duplex, and flow control. */
-       if (fullduplex == 1) {
+       if (fullduplex) {
                /* Configure IPG for full duplex operation. */
                printk(KERN_INFO "%s: setting full duplex, ", dev->name);
 
                mac_ctrl_val |= IPG_MC_DUPLEX_SELECT_FD;
 
-               if (txflowcontrol == 1) {
+               /* FIXME: Does this variable always equal fullduplex? */
+               if (txflowcontrol) {
                        printk("TX flow control");
                        mac_ctrl_val |= IPG_MC_TX_FLOW_CONTROL_ENABLE;
                } else {
@@ -540,7 +467,7 @@ static int ipg_config_autoneg(struct net_device *dev)
                        mac_ctrl_val &= ~IPG_MC_TX_FLOW_CONTROL_ENABLE;
                }
 
-               if (rxflowcontrol == 1) {
+               if (rxflowcontrol) {
                        printk(", RX flow control.");
                        mac_ctrl_val |= IPG_MC_RX_FLOW_CONTROL_ENABLE;
                } else {
@@ -568,9 +495,8 @@ static int ipg_config_autoneg(struct net_device *dev)
 static void ipg_nic_set_multicast_list(struct net_device *dev)
 {
        void __iomem *ioaddr = ipg_ioaddr(dev);
-       struct dev_mc_list *mc_list_ptr;
-       unsigned int hashindex;
-       u32 hashtable[2];
+       struct dev_mc_list *mc;
+       u32 hashtable[2] = { 0, 0 };
        u8 receivemode;
 
        IPG_DEBUG_MSG("_nic_set_multicast_list\n");
@@ -581,52 +507,34 @@ static void ipg_nic_set_multicast_list(struct net_device 
*dev)
                /* NIC to be configured in promiscuous mode. */
                receivemode = IPG_RM_RECEIVEALLFRAMES;
        } else if ((dev->flags & IFF_ALLMULTI) ||
-                  (dev->flags & IFF_MULTICAST &
-                   (dev->mc_count > IPG_MULTICAST_HASHTABLE_SIZE))) {
+                  (dev->flags & IFF_MULTICAST &&
+                   (dev->mc_count > 2*IPG_MULTICAST_HASHTABLE_SIZE))) {
                /* NIC to be configured to receive all multicast
                 * frames. */
                receivemode |= IPG_RM_RECEIVEMULTICAST;
-       } else if (dev->flags & IFF_MULTICAST & (dev->mc_count > 0)) {
+       } else if (dev->flags & IFF_MULTICAST && (dev->mc_count > 0)) {
                /* NIC to be configured to receive selected
                 * multicast addresses. */
                receivemode |= IPG_RM_RECEIVEMULTICASTHASH;
-       }
-
-       /* Calculate the bits to set for the 64 bit, IPG HASHTABLE.
-        * The IPG applies a cyclic-redundancy-check (the same CRC
-        * used to calculate the frame data FCS) to the destination
-        * address all incoming multicast frames whose destination
-        * address has the multicast bit set. The least significant
-        * 6 bits of the CRC result are used as an addressing index
-        * into the hash table. If the value of the bit addressed by
-        * this index is a 1, the frame is passed to the host system.
-        */
-
-       /* Clear hashtable. */
-       hashtable[0] = 0x00000000;
-       hashtable[1] = 0x00000000;
-
-       /* Cycle through all multicast addresses to filter. */
-       for (mc_list_ptr = dev->mc_list;
-            mc_list_ptr != NULL; mc_list_ptr = mc_list_ptr->next) {
-               /* Calculate CRC result for each multicast address. */
-               hashindex = crc32_le(0xffffffff, mc_list_ptr->dmi_addr,
-                                    ETH_ALEN);
 
-               /* Use only the least significant 6 bits. */
-               hashindex = hashindex & 0x3F;
-
-               /* Within "hashtable", set bit number "hashindex"
-                * to a logic 1.
+               /*
+                * The IPG uses the standard hash table technique to filter
+                * incoming multicast packets.  It computes the CRC of the
+                * incoming MAC address, and uses the low 6 bits of the
+                * result to select a hash table bit.  If set (and the address
+                * is a multicast address), the packet is received.
                 */
-               set_bit(hashindex, (void *)hashtable);
-       }
+               for (mc = dev->mc_list; mc; mv = mc->next) {
+                       /* Calculate CRC result for each multicast address. */
+                       u32 hashindex = crc32_le(0xffffffff, mc->dmi_addr,
+                                       ETH_ALEN);
 
-       /* Write the value of the hashtable, to the 4, 16 bit
-        * HASHTABLE IPG registers.
-        */
-       ipg_w32(hashtable[0], HASHTABLE_0);
-       ipg_w32(hashtable[1], HASHTABLE_1);
+                       /* Use low 6 bits to select hash table bit */
+                       set_bit(hashindex & 63, (void *)hashtable);
+               }
+               ipg_w32(hashtable[0], HASHTABLE_0);
+               ipg_w32(hashtable[1], HASHTABLE_1);
+       }
 
        ipg_w8(IPG_RM_RSVD_MASK & receivemode, RECEIVE_MODE);
 

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