linux-kernel - Re: [RFC PATCH v5 2/6] i2c: add helpers to ease DMA handling

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Date:   Thu, 21 Sep 2017 16:15:28 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-input@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH v5 2/6] i2c: add helpers to ease DMA handling


> > > +/**
> > > + * i2c_release_dma_safe_msg_buf - release DMA safe buffer and sync with i2c_msg
> > > + * @msg: the message to be synced with
> > > + * @buf: the buffer obtained from i2c_get_dma_safe_msg_buf(). May be NULL.
> > > + */
> > > +void i2c_release_dma_safe_msg_buf(struct i2c_msg *msg, u8 *buf)
> > > +{
> > > +	if (!buf || buf == msg->buf)
> > > +		return;
> > > +
> > > +	if (msg->flags & I2C_M_RD)
> > > +		memcpy(msg->buf, buf, msg->len);
> > > +
> > > +	kfree(buf);
> 
> Only free when you actually allocated it.  Seems to me like you need
> to check if (!(msg->flags & I2C_M_DMA_SAFE)) before kfree.
> 
> Otherwise the logic to do this will be needed in every driver
> which will get irritating fast.

Well, I return early if (buf == msg->buf) which is only true for
I2C_M_DMA_SAFE. If not, I allocated the buffer. Am I missing something?
It would be very strange to call this function if the caller allocated
the buffer manually.

Thanks for the review!


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