netdev - Re: [PATCH try#2] Blackfin ethernet driver: on chip ethernet MAC controller driver

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Date:	Sun, 15 Jul 2007 12:27:26 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	bryan.wu@...log.com
Cc:	Michael Buesch <mb@...sch.de>,
	Mike Frysinger <vapier.adi@...il.com>,
	Jeff Garzik <jeff@...zik.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH try#2] Blackfin ethernet driver: on chip ethernet MAC
 controller driver

Bryan Wu wrote:
> On Sun, 2007-07-15 at 14:17 +0200, Michael Buesch wrote:
>> On Sunday 15 July 2007 14:07:44 Bryan Wu wrote:
>>> @@ -483,9 +487,12 @@
>>>  
>>>  void setup_mac_addr(u8 * mac_addr)
>>>  {
>>> +	u32 addr_low = le32_to_cpu(*(u32 *) & mac_addr[0]);
>>> +	u16 addr_hi = le16_to_cpu(*(u16 *) & mac_addr[4]);
>>> +
>>>  	/* this depends on a little-endian machine */
>>> -	bfin_write_EMAC_ADDRLO(*(u32 *) & mac_addr[0]);
>>> -	bfin_write_EMAC_ADDRHI(*(u16 *) & mac_addr[4]);
>>> +	bfin_write_EMAC_ADDRLO(addr_low);
>>> +	bfin_write_EMAC_ADDRHI(addr_hi);
>>>  }
>>>  
>>>  static void adjust_tx_list(void)
>>> @@ -866,10 +873,10 @@
>>>  	int retval;
>>>  
>>>  	/* Grab the MAC address in the MAC */
>>> -	*(u32 *) (&(dev->dev_addr[0])) = bfin_read_EMAC_ADDRLO();
>>> -	*(u16 *) (&(dev->dev_addr[4])) = (u16) bfin_read_EMAC_ADDRHI();
>>> +	*(u32 *) (&(dev->dev_addr[0])) = cpu_to_le32(bfin_read_EMAC_ADDRLO());
>>> +	*(u16 *) (&(dev->dev_addr[4])) = cpu_to_le16((u16) bfin_read_EMAC_ADDRHI());
>> Try something like this:
>>
>> @@ -483,9 +487,12 @@
>>  
>>  void setup_mac_addr(u8 * mac_addr)
>>  {
>> +       u32 addr_low = le32_to_cpu(*(__le32 *) & mac_addr[0]);
>> +       u16 addr_hi = le16_to_cpu(*(__le16 *) & mac_addr[4]);
>> +
>> -       /* this depends on a little-endian machine */
>> -       bfin_write_EMAC_ADDRLO(*(u32 *) & mac_addr[0]);
>> -       bfin_write_EMAC_ADDRHI(*(u16 *) & mac_addr[4]);
>> +       bfin_write_EMAC_ADDRLO(addr_low);
>> +       bfin_write_EMAC_ADDRHI(addr_hi);
>>  }
>>  
>>  static void adjust_tx_list(void)
>> @@ -866,10 +873,10 @@
>>         int retval;
>>  
>>         /* Grab the MAC address in the MAC */
>> -       *(u32 *) (&(dev->dev_addr[0])) = bfin_read_EMAC_ADDRLO();
>> -       *(u16 *) (&(dev->dev_addr[4])) = (u16) bfin_read_EMAC_ADDRHI();
>> +       *(__le32 *) (&(dev->dev_addr[0])) = cpu_to_le32(bfin_read_EMAC_ADDRLO());
>> +       *(__le16 *) (&(dev->dev_addr[4])) = cpu_to_le16((u16) bfin_read_EMAC_ADDRHI());
>>
> 
> Thanks a lot, Michael. 
> 
> I got a generic question about this endianess check. When should use it
> in a driver or something else? I grep it in the driver/net/
> 
> ---
> drivers/net/e100.c:             ns->tx_window_errors += le32_to_cpu(s->tx_late_collisions);
> drivers/net/e100.c:             ns->tx_carrier_errors += le32_to_cpu(s->tx_lost_crs);
> drivers/net/e100.c:             ns->tx_fifo_errors += le32_to_cpu(s->tx_underruns);
> drivers/net/e100.c:             ns->tx_errors += le32_to_cpu(s->tx_max_collisions) +
> drivers/net/e100.c:                     le32_to_cpu(s->tx_lost_crs);
> drivers/net/e100.c:             ns->rx_length_errors += le32_to_cpu(s->rx_short_frame_errors) +
> drivers/net/e100.c:             ns->rx_crc_errors += le32_to_cpu(s->rx_crc_errors);
> drivers/net/e100.c:             ns->rx_frame_errors += le32_to_cpu(s->rx_alignment_errors);
> drivers/net/e100.c:             ns->rx_over_errors += le32_to_cpu(s->rx_overrun_errors);
> drivers/net/e100.c:             ns->rx_fifo_errors += le32_to_cpu(s->rx_overrun_errors);
> drivers/net/e100.c:             ns->rx_missed_errors += le32_to_cpu(s->rx_resource_errors);
> drivers/net/e100.c:             ns->rx_errors += le32_to_cpu(s->rx_crc_errors) +
> drivers/net/e100.c:                     le32_to_cpu(s->rx_alignment_errors) +
> drivers/net/e100.c:                     le32_to_cpu(s->rx_short_frame_errors) +
> drivers/net/e100.c:                     le32_to_cpu(s->rx_cdt_errors);
> drivers/net/e100.c:             nic->tx_deferred += le32_to_cpu(s->tx_deferred);
> drivers/net/e100.c:                     le32_to_cpu(s->tx_single_collisions);
> drivers/net/e100.c:                     le32_to_cpu(s->tx_multiple_collisions);
> drivers/net/e100.c:                     nic->tx_fc_pause += le32_to_cpu(s->fc_xmt_pause);
> drivers/net/e100.c:                     nic->rx_fc_pause += le32_to_cpu(s->fc_rcv_pause);
> drivers/net/e100.c:                             le32_to_cpu(s->fc_rcv_unsupported);
> drivers/net/e100.c:                             le32_to_cpu(cb->u.tcb.tbd.buf_addr),
> drivers/net/e100.c:                                     le32_to_cpu(cb->u.tcb.tbd.buf_addr),
> ---
> 
> Normally, it is used to protect some rx/tx status flags or dma buf addr.
> 
> Any guide line for this leXX_to_cpu usage?

It has to be used when accessing any data structure stored in RAM that 
the device will access and where byte order is significant. cpu_to_le32 
when writing to the RAM, le32_to_cpu when reading it. (or le16, etc. if 
needed).

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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