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SubjectRe: [PATCH V9 3/5] i2c: tegra: Add DMA support
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01.02.2019 22:22, Dmitry Osipenko пишет:
> 01.02.2019 22:20, Sowjanya Komatineni пишет:
>>
>>>> +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.
>>
>
> Ah, sorry. I missed that, seems good then.
>

BTW, it may be worthwhile to move out the error code handling into tegra_i2c_init_dma() for clarity. It also won't hurt to not ignore errors other than -ENODEV.

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 32d5744bce45..684a0689ac8d 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -397,7 +397,7 @@ static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev)
int err = 0;

if (!IS_ENABLED(CONFIG_TEGRA20_APB_DMA))
- return -ENODEV;
+ return 0;

dma_chan = dma_request_slave_channel_reason(i2c_dev->dev, "rx");
if (IS_ERR(dma_chan))
@@ -434,6 +434,13 @@ static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev)
if (i2c_dev->rx_dma_chan)
dma_release_channel(i2c_dev->rx_dma_chan);

+ /*
+ * -ENODEV is likely due to a missing "dmas" property, driver falls
+ * back to PIO in this case.
+ */
+ if (err == -ENODEV)
+ return 0;
+
return err;
}

@@ -1553,7 +1560,7 @@ static int tegra_i2c_probe(struct platform_device *pdev)
}

ret = tegra_i2c_init_dma(i2c_dev);
- if (ret == -EPROBE_DEFER)
+ if (ret)
goto disable_div_clk;

ret = tegra_i2c_init(i2c_dev, false);
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