netdev - Re: question about i2c_transfer() function (regarding mdio-i2c on RollBall SFPs)

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Message-ID: <20210107224211.4f01c055@nic.cz>
Date:   Thu, 7 Jan 2021 22:42:11 +0100
From:   Marek Behun <marek.behun@....cz>
To:     Wolfram Sang <wsa@...nel.org>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        Pali Rohár <pali@...nel.org>,
        linux-i2c@...r.kernel.org
Subject: Re: question about i2c_transfer() function (regarding mdio-i2c on
 RollBall SFPs)

On Thu, 7 Jan 2021 22:02:48 +0100
Wolfram Sang <wsa@...nel.org> wrote:

> > My question is whether this is allowed, whether the msgs array passed
> > to the i2c_transfer() function can have multiple msgs pointing to the
> > same buffer (the one into which the original page is first stored
> > with first i2c_msg and then restored from it in the last i2c_msg).  
> 
> Sending the messages is serialized, so the buffers won't interfere. At
> first glance, I think it would work this way. But it's late evening
> here, so I will have another look again tomorrow.
> 

I thought as much, but maybe there is some driver which can offload
whole i2c_transfer to HW, and has to pass the addresses of the buffers
to the HW, and the HW can have problems if the buffers overlap
somewhere...

Marek