linux-kernel - Re: [PATCH v2] i2c: rcar: add SMBus block read support

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Message-ID: <Ykcod/XOYvGfUsga@ninjato>
Date:   Fri, 1 Apr 2022 18:29:43 +0200
From:   Wolfram Sang <wsa+renesas@...g-engineering.com>
To:     "Gabbasov, Andrew" <Andrew_Gabbasov@...tor.com>
Cc:     "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "Surachari, Bhuvanesh" <Bhuvanesh_Surachari@...tor.com>
Subject: Re: [PATCH v2] i2c: rcar: add SMBus block read support

> >  	/* If next received data is the _LAST_, go to new phase. */
> > -	if (priv->pos + 1 == msg->len) {
> > +	if (priv->pos + 1 == msg->len && !recv_len_init) {
> 
> If a message contains a single byte after the length byte,
> when we come here after processing the length (in the same function call),
> "pos" is 1, "len" is 2, and we indeed are going to process the last byte.
> However, "recv_len_init" is still "true", and we skip these corresponding
> register writes, which is probably incorrect.
> The flag in this case should be re-set back to "false" after length
> processing and "pos" moving, but I think the variant in my patch

Confirmed. Tests fail with only one extra byte and clearing
'recv_len_init' fixes the issue. I don't think this is the proper
solution, though. I think it will create more readable code if we update
the checks. So people will understand what we are aiming for. The
current code is already implicit enough.


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