Re: [PATCH 2/2] i2c: i801: Replace waitqueue with completion API

[Heiner Kallweit <hkallweit1@gmail.com>]

On 25.05.2021 14:12, Jean Delvare wrote:
> Hi Heiner,
> 
> Adding Daniel Kurtz, who wrote the original wait queue-based code, to
> Cc. I'm not sure if Daniel is still into kernel code though.
> 
> On Sat, 22 May 2021 00:02:43 +0200, Heiner Kallweit wrote:
>> Using the completion API is more intuitive and it allows to simplify
>> the code. Note that we don't have to set priv->status = 0 any longer
>> with the completion API.
> 
> OK, but you need to call reinit_completion() instead, which has the
> same cost. So that's not a good argument ;-)
> 
Maybe my comment wasn't clear enough. I didn't want to say that we
save something but that it's safe from a functional point of view
to remove clearing priv->status.

>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>>  drivers/i2c/busses/i2c-i801.c | 48 ++++++++++++++---------------------
>>  1 file changed, 19 insertions(+), 29 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
>> index bfea94d02..738204d77 100644
>> --- a/drivers/i2c/busses/i2c-i801.c
>> +++ b/drivers/i2c/busses/i2c-i801.c
>> @@ -103,7 +103,7 @@
>>  #include <linux/dmi.h>
>>  #include <linux/slab.h>
>>  #include <linux/string.h>
>> -#include <linux/wait.h>
>> +#include <linux/completion.h>
>>  #include <linux/err.h>
>>  #include <linux/platform_device.h>
>>  #include <linux/platform_data/itco_wdt.h>
>> @@ -270,7 +270,7 @@ struct i801_priv {
>>  	unsigned int features;
>>  
>>  	/* isr processing */
>> -	wait_queue_head_t waitq;
>> +	struct completion done;
>>  	u8 status;
>>  
>>  	/* Command state used by isr for byte-by-byte block transactions */
>> @@ -496,24 +496,19 @@ static int i801_wait_byte_done(struct i801_priv *priv)
>>  static int i801_transaction(struct i801_priv *priv, int xact)
>>  {
>>  	int status;
>> -	int result;
>> +	unsigned long result;
>>  	const struct i2c_adapter *adap = &priv->adapter;
>>  
>> -	result = i801_check_pre(priv);
>> -	if (result < 0)
>> -		return result;
>> +	status = i801_check_pre(priv);
>> +	if (status < 0)
>> +		return status;
>>  
>>  	if (priv->features & FEATURE_IRQ) {
>> +		reinit_completion(&priv->done);
>>  		outb_p(xact | SMBHSTCNT_INTREN | SMBHSTCNT_START,
>>  		       SMBHSTCNT(priv));
>> -		result = wait_event_timeout(priv->waitq,
>> -					    (status = priv->status),
>> -					    adap->timeout);
>> -		if (!result)
>> -			status = -ETIMEDOUT;
>> -
>> -		priv->status = 0;
>> -		return i801_check_post(priv, status);
>> +		result = wait_for_completion_timeout(&priv->done, adap->timeout);
>> +		return i801_check_post(priv, result ? priv->status : -ETIMEDOUT);
>>  	}
>>  
>>  	/* the current contents of SMBHSTCNT can be overwritten, since PEC,
>> @@ -638,7 +633,7 @@ static irqreturn_t i801_host_notify_isr(struct i801_priv *priv)
>>   *      DEV_ERR - Invalid command, NAK or communication timeout
>>   *      BUS_ERR - SMI# transaction collision
>>   *      FAILED - transaction was canceled due to a KILL request
>> - *    When any of these occur, update ->status and wake up the waitq.
>> + *    When any of these occur, update ->status and signal completion.
>>   *    ->status must be cleared before kicking off the next transaction.
>>   *
>>   * 2) For byte-by-byte (I2C read/write) transactions, one BYTE_DONE interrupt
>> @@ -675,7 +670,7 @@ static irqreturn_t i801_isr(int irq, void *dev_id)
>>  	if (status) {
>>  		outb_p(status, SMBHSTSTS(priv));
>>  		priv->status = status;
>> -		wake_up(&priv->waitq);
>> +		complete(&priv->done);
>>  	}
>>  
>>  	return IRQ_HANDLED;
>> @@ -694,15 +689,15 @@ static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
>>  	int i, len;
>>  	int smbcmd;
>>  	int status;
>> -	int result;
>> +	unsigned long result;
>>  	const struct i2c_adapter *adap = &priv->adapter;
>>  
>>  	if (command == I2C_SMBUS_BLOCK_PROC_CALL)
>>  		return -EOPNOTSUPP;
>>  
>> -	result = i801_check_pre(priv);
>> -	if (result < 0)
>> -		return result;
>> +	status = i801_check_pre(priv);
>> +	if (status < 0)
>> +		return status;
>>  
>>  	len = data->block[0];
>>  
>> @@ -726,15 +721,10 @@ static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
>>  		priv->count = 0;
>>  		priv->data = &data->block[1];
>>  
>> +		reinit_completion(&priv->done);
>>  		outb_p(priv->cmd | SMBHSTCNT_START, SMBHSTCNT(priv));
>> -		result = wait_event_timeout(priv->waitq,
>> -					    (status = priv->status),
>> -					    adap->timeout);
>> -		if (!result)
>> -			status = -ETIMEDOUT;
>> -
>> -		priv->status = 0;
>> -		return i801_check_post(priv, status);
>> +		result = wait_for_completion_timeout(&priv->done, adap->timeout);
>> +		return i801_check_post(priv, result ? priv->status : -ETIMEDOUT);
>>  	}
>>  
>>  	for (i = 1; i <= len; i++) {
>> @@ -1889,7 +1879,7 @@ static int i801_probe(struct pci_dev *dev, const struct pci_device_id *id)
>>  	}
>>  
>>  	if (priv->features & FEATURE_IRQ) {
>> -		init_waitqueue_head(&priv->waitq);
>> +		init_completion(&priv->done);
>>  
>>  		err = devm_request_irq(&dev->dev, dev->irq, i801_isr,
>>  				       IRQF_SHARED,
> 
> The clean-up isn't massive but I agree the code is a bit more pleasant
> to read after the change, and I also see the binary size shrink a bit,
> so I vote for it.
> 
> Reviewed-by: Jean Delvare <jdelvare@suse.de>
> Tested-by: Jean Delvare <jdelvare@suse.de>
>