linux-kernel - RE: [PATCH V9 3/5] i2c: tegra: Add DMA support

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Message-ID: <BYAPR12MB339865C0876E1BF7278DC7C8C2920@BYAPR12MB3398.namprd12.prod.outlook.com>
Date:   Fri, 1 Feb 2019 20:21:39 +0000
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>,
        Shardar Mohammed <smohammed@...dia.com>,
        Timo Alho <talho@...dia.com>
CC:     "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: RE: [PATCH V9 3/5] i2c: tegra: Add DMA support


>	rx_chan = dma_request_slave_channel_reason(i2c_dev->dev, "rx");
>	if (IS_ERR(rx_chan))
>		return PTR_ERR(rx_chan);
>
>
> > +
> > +	dma_chan = dma_request_slave_channel_reason(i2c_dev->dev, "tx");
> > +	if (IS_ERR(dma_chan)) {
> > +		err = PTR_ERR(dma_chan);
> > +		goto error;
>
> It's a good practice to release resources in opposite order to the allocation. Hence better to write this as:
>
>		goto err_release_rx;
>
> > +	}
> > +
> > +	i2c_dev->tx_dma_chan = dma_chan;
> > +
> > +	dma_buf = dma_alloc_coherent(i2c_dev->dev,
> > +				     i2c_dev->dma_buf_size, &dma_phys,
> > +				     GFP_KERNEL | __GFP_NOWARN);
> > +
> > +	if (!dma_buf) {
> > +		dev_err(i2c_dev->dev, "failed to allocate the DMA buffer\n");
> > +		err = -ENOMEM;
> > +		goto error;
>
>		goto err_release_tx;
>
> > +	}
> > +
> > +	i2c_dev->dma_buf = dma_buf;
> > +	i2c_dev->dma_phys = dma_phys;	i2c_dev->rx_dma_chan = rx_chan;
>	i2c_dev->tx_dma_chan = tx_chan;
>
> > +	return 0;
> > +
> > +error:
> > +	if (i2c_dev->tx_dma_chan)
> > +		dma_release_channel(i2c_dev->tx_dma_chan);
> > +
> > +	if (i2c_dev->rx_dma_chan)
> > +		dma_release_channel(i2c_dev->rx_dma_chan);
>
> error_release_tx:
>	dma_release_channel(tx_chan);
> error_release_rx:
>	dma_release_channel(rx_chan);
>
> > +
> > +	return err;

I am releasing resources in reverse order to allocation.
Trying for rx allocation followed by tx allocation
During release releasing tx and then rx.
In case if tx allocation fails, doesn’t go thru release. If rx or buf allocation fails, releases tx first and then rx