netdev - Re: [RFC PATCH V4 net-next 1/5] ethtool: Allow network drivers to dump arbitrary EEPROM data

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Date:   Tue, 23 Mar 2021 03:03:56 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Don Bollinger <don@...bollingers.org>
Cc:     'Moshe Shemesh' <moshe@...dia.com>,
        "'David S. Miller'" <davem@...emloft.net>,
        'Jakub Kicinski' <kuba@...nel.org>,
        'Adrian Pop' <pop.adrian61@...il.com>,
        'Michal Kubecek' <mkubecek@...e.cz>, netdev@...r.kernel.org,
        'Vladyslav Tarasiuk' <vladyslavt@...dia.com>
Subject: Re: [RFC PATCH V4 net-next 1/5] ethtool: Allow network drivers to
 dump arbitrary EEPROM data

> > I don't even see a need for this. The offset should be within one 1/2
> page, of
> > one bank. So offset >= 0 and <= 127. Length is also > 0 and
> > <- 127. And offset+length is <= 127.
> 
> I like the clean approach, but...   How do you request low memory?

Duh!

I got my conditions wrong. Too focused on 1/2 pages to think that two
of them makes one page!

Lets try again:

offset < 256
0 < len < 128

if (offset < 128)
   offset + len < 128
else
   offset + len < 256

Does that look better?

Reading bytes from the lower 1/2 of page 0 should give the same data
as reading data from the lower 1/2 of page 42. So we can allow that,
but don't be too surprised when an SFP gets it wrong and gives you
rubbish. I would suggest ethtool(1) never actually does read from the
lower 1/2 of any page other than 0.

And i agree about documentation. I would suggest a comment in
ethtool_netlink.h, and the RST documentation.

		   Andrew