linux-kernel - Re: [PATCH V1 6/6] i2c: tegra: remove BUG, BUG

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Message-ID: <40f730a0-d602-fe94-8e20-3e209b1c9eda@nvidia.com>
Date:   Fri, 7 Jun 2019 12:24:12 -0700
From:   Bitan Biswas <bbiswas@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        <linux-i2c@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Peter Rosin <peda@...ntia.se>,
        Wolfram Sang <wsa@...-dreams.de>
CC:     Shardar Mohammed <smohammed@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>
Subject: Re: [PATCH V1 6/6] i2c: tegra: remove BUG, BUG_ON



On 6/7/19 11:55 AM, Bitan Biswas wrote:
> 
> 
> On 6/7/19 5:18 AM, Dmitry Osipenko wrote:
>> 07.06.2019 15:12, Dmitry Osipenko пишет:
>>> 07.06.2019 15:08, Dmitry Osipenko пишет:
>>>> 07.06.2019 14:55, Bitan Biswas пишет:
>>>>> Remove redundant BUG_ON calls or replace with WARN_ON_ONCE
>>>>> as needed. Replace BUG() with error handling code.
>>>>> Define I2C_ERR_UNEXPECTED_STATUS for error handling.
>>>>>
>>>>> Signed-off-by: Bitan Biswas <bbiswas@...dia.com>
>>>>> ---
>>>>>   drivers/i2c/busses/i2c-tegra.c | 15 ++++++++-------
>>>>>   1 file changed, 8 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/drivers/i2c/busses/i2c-tegra.c 
>>>>> b/drivers/i2c/busses/i2c-tegra.c
>>>>> index 4dfb4c1..c407bd7 100644
>>>>> --- a/drivers/i2c/busses/i2c-tegra.c
>>>>> +++ b/drivers/i2c/busses/i2c-tegra.c
>>>>> @@ -73,6 +73,7 @@
>>>>>   #define I2C_ERR_NO_ACK                BIT(0)
>>>>>   #define I2C_ERR_ARBITRATION_LOST        BIT(1)
>>>>>   #define I2C_ERR_UNKNOWN_INTERRUPT        BIT(2)
>>>>> +#define I2C_ERR_UNEXPECTED_STATUS        BIT(3)
>>>>>   #define PACKET_HEADER0_HEADER_SIZE_SHIFT    28
>>>>>   #define PACKET_HEADER0_PACKET_ID_SHIFT        16
>>>>> @@ -515,7 +516,6 @@ static int tegra_i2c_empty_rx_fifo(struct 
>>>>> tegra_i2c_dev *i2c_dev)
>>>>>        * prevent overwriting past the end of buf
>>>>>        */
>>>>>       if (rx_fifo_avail > 0 && buf_remaining > 0) {
>>>>> -        BUG_ON(buf_remaining > 3);
>>>>>           val = i2c_readl(i2c_dev, I2C_RX_FIFO);
>>>>>           val = cpu_to_le32(val);
>>>>>           memcpy(buf, &val, buf_remaining);
>>>>> @@ -523,7 +523,6 @@ static int tegra_i2c_empty_rx_fifo(struct 
>>>>> tegra_i2c_dev *i2c_dev)
>>>>>           rx_fifo_avail--;
>>>>>       }
>>>>> -    BUG_ON(rx_fifo_avail > 0 && buf_remaining > 0);
>>>>>       i2c_dev->msg_buf_remaining = buf_remaining;
>>>>>       i2c_dev->msg_buf = buf;
>>>>> @@ -581,7 +580,6 @@ static int tegra_i2c_fill_tx_fifo(struct 
>>>>> tegra_i2c_dev *i2c_dev)
>>>>>        * boundary and fault.
>>>>>        */
>>>>>       if (tx_fifo_avail > 0 && buf_remaining > 0) {
>>>>> -        BUG_ON(buf_remaining > 3);
>>>>>           memcpy(&val, buf, buf_remaining);
>>>>>           val = le32_to_cpu(val);
>>>>> @@ -847,10 +845,13 @@ static irqreturn_t tegra_i2c_isr(int irq, 
>>>>> void *dev_id)
>>>>>       if (!i2c_dev->is_curr_dma_xfer) {
>>>>>           if (i2c_dev->msg_read && (status & 
>>>>> I2C_INT_RX_FIFO_DATA_REQ)) {
>>>>> -            if (i2c_dev->msg_buf_remaining)
>>>>> +            if (i2c_dev->msg_buf_remaining) {
>>>>>                   tegra_i2c_empty_rx_fifo(i2c_dev);
>>>>> -            else
>>>>> -                BUG();
>>>>> +            } else {
>>>>> +                dev_err(i2c_dev->dev, "unexpected rx data 
>>>>> request\n");
>>>>> +                i2c_dev->msg_err |= I2C_ERR_UNEXPECTED_STATUS;
>>>>> +                goto err;
>>>>> +            }
>>>>>           }
>>>>>           if (!i2c_dev->msg_read && (status & 
>>>>> I2C_INT_TX_FIFO_DATA_REQ)) {
>>>>> @@ -876,7 +877,7 @@ static irqreturn_t tegra_i2c_isr(int irq, void 
>>>>> *dev_id)
>>>>>       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);
>>>>> +        WARN_ON_ONCE(i2c_dev->msg_buf_remaining);
>>>>>           complete(&i2c_dev->msg_complete);
>>>>>       }
>>>>>       goto done;
>>>>>
>>>>
>>>> Very nice, thank you very much! BTW, I think it may worth to add 
>>>> another
>>>> patch that will reset hardware state in a case of the warning since we
>>>> know that something gone wrong.
>>>>
>>>> Reviewed-by: Dmitry Osipenko <digetx@...il.com>
>>>>
>>>
>>> Something like that:
>>>
>>>       complete(&i2c_dev->msg_complete);
>>>
>>>     if (WARN_ON_ONCE(i2c_dev->msg_buf_remaining))
>>>         goto err;
>>>
>>
>> Ah, that's inside the ISR, so maybe will make sense to just not complete
>> the transfer and let it timeout:
>>
>>     if (!WARN_ON_ONCE(i2c_dev->msg_buf_remaining))
>>         complete(&i2c_dev->msg_complete);
> OK. I shall send the updated patch.
I see that there is already err label in the ISR that could be jumped 
into. Hence, planning to share updated patch with the error handling.

-regards,
  Bitan