netdev - Re: [PATCH 1/1] net: Add Aeroflex Gaisler GRETH 10/100/1G Ethernet MAC driver

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Message-ID: <4B4B4FFA.8070805@gaisler.com>
Date:	Mon, 11 Jan 2010 17:21:14 +0100
From:	Kristoffer Glembo <kristoffer@...sler.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] net: Add Aeroflex Gaisler GRETH 10/100/1G Ethernet
 MAC driver

Hi Ben,

Thanks for the feedback.

Ben Hutchings wrote:
> On Fri, 2010-01-08 at 16:45 +0100, Kristoffer Glembo wrote:
> [...]
>> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
>> index dd9a09c..806c127 100644
>> --- a/drivers/net/Kconfig
>> +++ b/drivers/net/Kconfig
> 
> This is just about the worst possible way to configure the MAC address.
> You should be getting it from EEPROM/flash or OpenFirmware properties.

Yes sorry for that ugliness. I will change this to OF properties.

> Is this driver really so good that we should configure it twice?
> 

Maybe not :) .. but I wanted it to show up both in 10/100 and
1000 Mbps since it supports two different devices. But I read in
Kconfig now that it then should be only in 10/100. That's fine.

> [...] 
>> diff --git a/drivers/net/greth.c b/drivers/net/greth.c

>> +#define GRETH_REGLOAD(a)	    (__raw_readl(&(a)))
>> +#define GRETH_REGSAVE(a, v)         (__raw_writel(v, &(a)))
>> +#define GRETH_REGORIN(a, v)         (GRETH_REGSAVE(a, (GRETH_REGLOAD(a) | (v))))
>> +#define GRETH_REGANDIN(a, v)        (GRETH_REGSAVE(a, (GRETH_REGLOAD(a) & (v))))
> 
> I think you need an mmiowb() after the __raw_writel().
> Also, are you sure the registers are going to match host byte order?

I'm working on a CPU with strong ordering so I'm not so confident in these matters,
but as I understand it I should in that case not put mmiowb() after each __raw_writel()
but only before unlocks where mmio has been done in the critical section.

I have not put a single explicit memory barrier in the code, I was under the 
impression that each architecture that needs it has it in the __raw_writel. 
I only used the __raw versions since I wanted native byte ordering. I should add
cpu_to_be32 and be32_to_cpu however as you point out. Questions is do I need to add
wmb/mb when I use __raw as well?

> Use print_hex_dump().
> 

Ah nice, thanks!

>> +
>> +			pr_debug(" %.2x", *((unsigned char *)
>> +					    (phys_to_virt
>> +					     (skb_shinfo(skb)->frags[i].page) +
>> +					     skb_shinfo(skb)->frags[i].page_offset + j)));
> 
> WTF?  phys_to_virt() does not work on pointers to struct page.

Oops. Some untested code crept in here. Adding page_to_phys.

I will fix the other issues you mentioned and resend the patch.

Best regards,
Kristoffer Glembo

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