linux-kernel - Re: [PATCH V2 6/6] i2c: tegra: remove BUG, BUG

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Message-ID: <8daef4be-f841-bb9a-3865-9cc6bf9c51c5@nvidia.com>
Date:   Sun, 9 Jun 2019 20:52:38 -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 V2 6/6] i2c: tegra: remove BUG, BUG_ON



On 6/7/19 12:47 PM, Dmitry Osipenko wrote:
> 07.06.2019 22:30, 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 | 16 +++++++++-------
>>   1 file changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>> index 4dfb4c1..c89d0ee 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 +877,8 @@ 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);
>> +		if (WARN_ON_ONCE(i2c_dev->msg_buf_remaining))
>> +			goto err;
>>   		complete(&i2c_dev->msg_complete);
>>   	}
>>   	goto done;
>>
> 
> Unfortunately that's not enough because the indicator of the error is
> the i2c_dev->msg_err and no error is set in yours case, hence no
> hardware reset will be performed. It should be at least somewhat like this:
> 
> 	if (WARN_ON_ONCE(i2c_dev->msg_buf_remaining)) {
> 		i2c_dev->msg_err |= I2C_ERR_UNKNOWN_INTERRUPT;
> 		goto err;
> 	}
> 
Fine. I shall set msg_err as I2C_ERR_UNKNOWN_INTERRUPT instead of 
I2C_ERR_UNEXPECTED_STATUS for condition of non-zero msg_bug_remaining in 
PIO mode with transfer complete interrupt.


-Thanks,
  Bitan