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

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Date:   Thu, 31 Jan 2019 20:38:29 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.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

31.01.2019 20:25, Dmitry Osipenko пишет:
> 31.01.2019 20:11, Dmitry Osipenko пишет:
>> 31.01.2019 19:56, Sowjanya Komatineni пишет:
>>>
>>>>>>  drivers/i2c/busses/Kconfig     |   2 +-
>>>>>>  drivers/i2c/busses/i2c-tegra.c | 362 
>>>>>> ++++++++++++++++++++++++++++++++++++++---
>>>>>>  2 files changed, 339 insertions(+), 25 deletions(-)
>>>>>
>>>>> Tegra20 crashes because of this patch:
>>>>>
>>>> [snip]
>>>>> <4>[    3.395915] ------------[ cut here ]------------
>>>>> <2>[    3.395919] kernel BUG at drivers/i2c/busses/i2c-tegra.c:810!
>>>> The BUG line is from:
>>>>
>>>> 	if (status & I2C_INT_PACKET_XFER_COMPLETE) {
>>>> 		if (i2c_dev->is_curr_dma_xfer)
>>>> 			i2c_dev->msg_buf_remaining = 0;
>>>> 		BUG_ON(i2c_dev->msg_buf_remaining);
>>>> 		complete(&i2c_dev->msg_complete);
>>>> 	}
>>>>
>>> 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.
> 

Also, enforcing dma=true regardless of transfer size doesn't work as well.