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    SubjectRe: [PATCH V19 5/7] i2c: tegra: Add DMA support
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    On 12/02/2019 19:06, Sowjanya Komatineni wrote:
    > This patch adds DMA support for Tegra I2C.
    >
    > Tegra I2C TX and RX FIFO depth is 8 words. PIO mode is used for
    > transfer size of the max FIFO depth and DMA mode is used for
    > transfer size higher than max FIFO depth to save CPU overhead.
    >
    > PIO mode needs full intervention of CPU to fill or empty FIFO's
    > and also need to service multiple data requests interrupt for the
    > same transaction. This adds delay between data bytes of the same
    > transfer when CPU is fully loaded and some slave devices has
    > internal timeout for no bus activity and stops transaction to
    > avoid bus hang. DMA mode is helpful in such cases.
    >
    > DMA mode is also helpful for Large transfers during downloading or
    > uploading FW over I2C to some external devices.
    >
    > Tegra210 and prior Tegra chips use APBDMA driver which is replaced
    > with GPCDMA on Tegra186 and Tegra194.
    > This patch uses has_apb_dma flag in hw_feature to differentiate
    > DMA driver change between Tegra chipset.
    >
    > APBDMA driver is registered from module-init level and this patch
    > also has a change to register I2C driver at module-init level
    > rather than subsys-init to avoid deferring I2C probe till APBDMA
    > driver is registered.
    >
    > Acked-by: Thierry Reding <treding@nvidia.com>
    > Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
    > Tested-by: Dmitry Osipenko <digetx@gmail.com>
    > Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>

    ...

    > +static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev)
    > +{
    > + struct dma_chan *chan;
    > + u32 *dma_buf;
    > + dma_addr_t dma_phys;
    > + int err;
    > +
    > + if (!IS_ENABLED(CONFIG_TEGRA20_APB_DMA) ||
    > + !i2c_dev->hw->has_apb_dma) {
    > + err = -ENODEV;
    > + goto err_out;
    > + }
    > +
    > + chan = dma_request_slave_channel_reason(i2c_dev->dev, "rx");
    > + if (IS_ERR(chan)) {
    > + err = PTR_ERR(chan);
    > + goto err_out;
    > + }
    > +
    > + i2c_dev->rx_dma_chan = chan;
    > +
    > + chan = dma_request_slave_channel_reason(i2c_dev->dev, "tx");
    > + if (IS_ERR(chan)) {
    > + err = PTR_ERR(chan);
    > + goto err_out;
    > + }
    > +
    > + i2c_dev->tx_dma_chan = 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 err_out;
    > + }
    > +
    > + i2c_dev->dma_buf = dma_buf;
    > + i2c_dev->dma_phys = dma_phys;
    > + return 0;
    > +
    > +err_out:
    > + tegra_i2c_release_dma(i2c_dev);
    > + if (err != -EPROBE_DEFER) {
    > + dev_err(i2c_dev->dev, "cannot use DMA: %d\n", err);
    > + dev_err(i2c_dev->dev, "fallbacking to PIO\n");
    > + return 0;
    > + }
    I think that the above should be a dev_dbg print or re-worked in someway
    because now for Tegra194 which does not have an APB DMA I see ...

    [ 6.093234] ERR KERN tegra-i2c 31c0000.i2c: cannot use DMA: -19
    [ 6.096847] ERR KERN tegra-i2c 31c0000.i2c: falling back to PIO

    Given that the APB DMA is not supported for Tegra186/Tegra194, there is
    no point in printing these error messages. Now it looks like something
    is wrong but really it is not :-(

    Cheers
    Jon

    --
    nvpublic

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