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

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Date:   Thu, 31 Jan 2019 20:25:54 +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 20:11, 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.