linux-kernel - Re: [PATCH 09/12] i2c: qup: fix buffer overflow for multiple msg of maximum xfer len

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Message-ID: <20180227231559.GJ20901@hector.attlocal.net>
Date:   Tue, 27 Feb 2018 17:15:59 -0600
From:   Andy Gross <andy.gross@...aro.org>
To:     Abhishek Sahu <absahu@...eaurora.org>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        David Brown <david.brown@...aro.org>,
        Sricharan R <sricharan@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/12] i2c: qup: fix buffer overflow for multiple msg of
 maximum xfer len

On Sat, Feb 03, 2018 at 01:28:14PM +0530, Abhishek Sahu wrote:
> The BAM mode requires buffer for start tag data and tx, rx SG
> list. Currently, this is being taken for maximum transfer length
> (65K). But an I2C transfer can have multiple messages and each
> message can be of this maximum length so the buffer overflow will
> happen in this case. Since increasing buffer length won’t be
> feasible since an I2C transfer can contain any number of messages
> so this patch does following changes to make i2c transfers working
> for multiple messages case.
> 
> 1. Calculate the required buffers for 2 maximum length messages
>    (65K * 2).
> 2. Split the descriptor formation and descriptor scheduling.
>    The idea is to fit as many messages in one DMA transfers for 65K
>    threshold value (max_xfer_sg_len). Whenever the sg_cnt is
>    crossing this, then schedule the BAM transfer and subsequent
>    transfer will again start from zero.
> 
> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>

I'm ok with this patch.  I find the idea of a > 64k size message to be something
that usually wouldn't be encountered, but... with some eeproms and maybe TPMs
perhaps this could happen?

Reviewed-by: Andy Gross <andy.gross@...aro.org>