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

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Message-ID: <e50a353c-94c4-1a47-92a4-5f41f4f64aa7@gmail.com>
Date:   Thu, 31 Jan 2019 20:11:29 +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 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.