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

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Message-ID: <BYAPR12MB33984FB81B8BB1EC8C0C4908C2920@BYAPR12MB3398.namprd12.prod.outlook.com>
Date:   Fri, 1 Feb 2019 19:20:01 +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


> > +static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev) {
> > +	struct dma_chan *dma_chan;
> > +	u32 *dma_buf;
> > +	dma_addr_t dma_phys;
> > +	int err = 0;
> > +
> > +	if (!IS_ENABLED(CONFIG_TEGRA20_APB_DMA))
> > +		return -ENODEV;
>
> Driver shall not fail to probe if DMA driver is disabled, but to continue with the PIO-only mode available.
>
> Should be:
>
>	if (!IS_ENABLED(CONFIG_TEGRA20_APB_DMA))
>		return 0;
>
Except EPROBE_DEFER, anything else returned from tegra_i2c_init_dma (ENODEV/ENOMEM) is ignored in i2c_probe
DMA mode decision is based on xfer size and availability of dma channel or can be changed based on valid dma buf to shorten the line.