[PATCH RESEND] natsemi: fix timing issue for reading mac from eeprom via dp8381x

[PATCH RESEND] natsemi: fix timing issue for reading mac from eeprom via dp8381x

[Roland Kletzing]

Natsemi driver does not read MAC correctly from eeprom, while natsemi-diag
from nictools-pci does. Apparently, it`s a timing issue in the kernel driver.

According to ftp://ftp.gwdg.de/pub/linux/misc/donald.becker/diag/natsemi-diag.c
, eeprom_delay(ee_addr) is defined as follows:

/* Delay between EEPROM clock transitions.
This flushes the write buffer to prevent quick double-writes.
*/
#define eeprom_delay(ee_addr) inl(ee_addr); inl(ee_addr)

while in the natsemi linux kernel driver, the delay is done this way :

#define eeprom_delay(ee_addr) readl(ee_addr)

, which results in the MAC being all zero`s on my systems (old Geode GX1 board 
like being used in Compaq Evo T20 or Wyse WT3235LE Thin Clients).

So i simply added a second readl() to increase delay (instead of turning into 
inl() as proposed before). This may look a little bit ugly, but it`s fixing the
problem for me.

I´m not sure how many natsemi users being left on this planet (probably few),
but i guess this change does not do any harm on platforms where the driver does
not behave buggy, so please consider adding it to mainline/stable/longterm.


BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=51791
Reported-by: Roland Kletzing <devzero@web.de>
Signed-off-by: Roland Kletzing <devzero@web.de>

---
drivers/net/ethernet/natsemi/natsemi.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/natsemi/natsemi.c b/drivers/net/ethernet/natsemi/natsemi.c
index b83f7c0..96f0029 100644
--- a/drivers/net/ethernet/natsemi/natsemi.c
+++ b/drivers/net/ethernet/natsemi/natsemi.c
@@ -987,7 +987,7 @@ static int natsemi_probe1(struct pci_dev *pdev, const struct pci_device_id *ent)
    The old method of using an ISA access as a delay, __SLOW_DOWN_IO__, is
    deprecated.
 */
-#define eeprom_delay(ee_addr)  readl(ee_addr)
+#define eeprom_delay(ee_addr)  readl(ee_addr);  readl(ee_addr)

 #define EE_Write0 (EE_ChipSelect)
 #define EE_Write1 (EE_ChipSelect | EE_DataIn)
--

Re: [PATCH RESEND] natsemi: fix timing issue for reading mac from eeprom via dp8381x

[David Miller]

From: "Roland Kletzing" <devzero@web.de>
Date: Wed, 19 Nov 2014 23:26:11 +0100

> diff --git a/drivers/net/ethernet/natsemi/natsemi.c b/drivers/net/ethernet/natsemi/natsemi.c
> index b83f7c0..96f0029 100644
> --- a/drivers/net/ethernet/natsemi/natsemi.c
> +++ b/drivers/net/ethernet/natsemi/natsemi.c
> @@ -987,7 +987,7 @@ static int natsemi_probe1(struct pci_dev *pdev, const struct pci_device_id *ent)
>     The old method of using an ISA access as a delay, __SLOW_DOWN_IO__, is
>     deprecated.
>  */
> -#define eeprom_delay(ee_addr)  readl(ee_addr)
> +#define eeprom_delay(ee_addr)  readl(ee_addr);  readl(ee_addr)

Your email client has corrupted this patch, changing TAB characters
into sequences of spaces.

Also, you should not just have a macro expanding to two statements,
because now things like:

	if (x)
		eeprom_delay(addr);

doesn't do what you intended.

Either make this an inline function, or enclose the two readl()
statements inside of a "do { } while (0)"