linux-kernel - RE: [PATCH V8 3/5] i2c: tegra: Add DMA Support

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Date:   Thu, 31 Jan 2019 17:38:50 +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 V8 3/5] i2c: tegra: Add DMA Support



>>>
>> BUG_ON line is not part of this change. It was already there in existing driver.
>> Based on log, I see DMA transfer is done for 224 bytes followed by 1 successful PIO transfer and then on next PIO transfer it received packet xfer complete interrupt with incomplete transfer bytes and that where it hit BUG_ON condition.
>>
>>
> 
> Yes, that BUG_ON is caused by the DMA transferring. Everything works fine be setting dma=false in the code, hence it's likely not a bug in the code (at least for now it looks fine), but likely that HW is not programmed correctly.
> 

> It works with this change:
>
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c index fe5b89abc576..8e059e94b94e 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -1170,10 +1170,11 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
>                 time_left, completion_done(&i2c_dev->msg_complete),
>                 i2c_dev->msg_err);
>
> +       tegra_i2c_init(i2c_dev, true);
> +
>         if (likely(i2c_dev->msg_err == I2C_ERR_NONE))
>                 return 0;
>  
> -       tegra_i2c_init(i2c_dev, true);
>         /* start recovery upon arbitration loss in single master mode */
>         if (i2c_dev->msg_err == I2C_ERR_ARBITRATION_LOST) {
>                 if (!i2c_dev->is_multimaster_mode)
>
>
> Which means that HW state is kept dirty after DMA transfer. Please check everything carefully.

FIFO trigger levels are diff for PIO Vs DMA so it need to be moved to xfer function. Will fix that.