Re: [PATCH for-next v4 05/12] RDMA/erdma: Add cmdq implementation

[Cheng Xu <chengyou@linux.alibaba.com>]

On 3/18/22 8:57 PM, Wenpeng Liang wrote:
> On 2022/3/14 14:47, Cheng Xu wrote:
>> Cmdq is the main control plane channel between erdma driver and hardware.
>> After erdma device is initialized, the cmdq channel will be active in the
>> whole lifecycle of this driver.
> 
> <...>
> 
>> +static int erdma_poll_cmd_completion(struct erdma_comp_wait *comp_ctx,
>> +				     struct erdma_cmdq *cmdq, u32 timeout)
>> +{
>> +	unsigned long comp_timeout = jiffies + msecs_to_jiffies(timeout);
>> +
>> +	while (1) {
>> +		erdma_polling_cmd_completions(cmdq);
>> +		if (comp_ctx->cmd_status != ERDMA_CMD_STATUS_ISSUED)
>> +			break;
>> +
>> +		if (time_is_before_jiffies(comp_timeout))
>> +			return -ETIME;
>> +
>> +		msleep(20);
>> +	}
> 
> Here I feel confused, why not use time_after as an exit condition?
> I would be grateful if you explain this timeout exit mechanism.
> 

They are the same, You can review the definition in <linux/jiffies.h> :

/* time_is_before_jiffies(a) return true if a is before jiffies */
#define time_is_before_jiffies(a) time_after(jiffies, a)


Thanks,
Cheng Xu

> Thanks,
> Wenpeng