Subject: Re: [PATCH 2/6] ibmvscsi: Add and use enums for valid CRQ header values

From: Tyrel Datwyler <[email-masked]>
Date: Thu, 4 Feb 2016 13:25:21 -0800

On 02/04/2016 11:55 AM, Manoj Kumar wrote:
> On 2/3/2016 5:28 PM, Tyrel Datwyler wrote:
>> The PAPR defines four valid header values for the first byte of a
>> CRQ message. Namely, an unused/empty message (0x00), a valid
>> command/response entry (0x80), a valid initialization entry (0xC0),
>> and a transport event (0xFF). Define these values as enums and use
>> them in the code in place of their magic number equivalents.
>>
>> Signed-off-by: Tyrel Datwyler <[email-masked]>
>> ---
>>   drivers/scsi/ibmvscsi/ibmvscsi.c | 14 +++++++-------
>>   drivers/scsi/ibmvscsi/viosrp.h   |  7 +++++++
>>   2 files changed, 14 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/scsi/ibmvscsi/ibmvscsi.c b/drivers/scsi/ibmvscsi/ibmvscsi.c
>> index adfef9d..176260d 100644
>> --- a/drivers/scsi/ibmvscsi/ibmvscsi.c
>> +++ b/drivers/scsi/ibmvscsi/ibmvscsi.c
>> @@ -182,7 +182,7 @@ static struct viosrp_crq *crq_queue_next_crq(struct crq_queue *queue)
>>
>>   	spin_lock_irqsave(&queue->lock, flags);
>>   	crq = &queue->msgs[queue->cur];
>> -	if (crq->valid & 0x80) {
>> +	if (crq->valid & VIOSRP_CRQ_VALID) {
> 
> After the switch to enums, bitwise operators are a bit misleading.
> Especially in this case since multiple values would satisfy this
> condition: VIOSRP_CRQ_VALID, VIOSRP_CRQ_INIT and
> VIOSRP_CRQ_TRANSPORT.

Yeah, I can see how that is confusing. Since, all three possible valid
crq message types have the first bit set I think this was originally a
cute hack to grab anything that was likely valid. Then in
ibmvscsi_handle_crq() we explicitly match the full header value in a
switch statement logging anything that turned out actually invalid.

> 
> If 'valid' will only have one of these four enums defined, would
> this be better written as:
> 
> 	if (crq->valid != VIOSRP_CRQ_FREE)

This definitely would make the logic easier to read and follow. Also,
this would make sure any crq with an invalid header that doesn't have
its first bit set will also be logged by the ibmvscsi_handle_crq()
switch statement default block and not silently ignored.

-Tyrel

> 
>>   		if (++queue->cur == queue->size)
>>   			queue->cur = 0;
>>
>> @@ -231,7 +231,7 @@ static void ibmvscsi_task(void *data)
>>   		/* Pull all the valid messages off the CRQ */
>>   		while ((crq = crq_queue_next_crq(&hostdata->queue)) != NULL) {
>>   			ibmvscsi_handle_crq(crq, hostdata);
>> -			crq->valid = 0x00;
>> +			crq->valid = VIOSRP_CRQ_FREE;
>>   		}
>>
>>   		vio_enable_interrupts(vdev);
>> @@ -239,7 +239,7 @@ static void ibmvscsi_task(void *data)
>>   		if (crq != NULL) {
>>   			vio_disable_interrupts(vdev);
>>   			ibmvscsi_handle_crq(crq, hostdata);
>> -			crq->valid = 0x00;
>> +			crq->valid = VIOSRP_CRQ_FREE;
>>   		} else {
>>   			done = 1;
>>   		}
>> @@ -474,7 +474,7 @@ static int initialize_event_pool(struct event_pool *pool,
>>   		struct srp_event_struct *evt = &pool->events[i];
>>   		memset(&evt->crq, 0x00, sizeof(evt->crq));
>>   		atomic_set(&evt->free, 1);
>> -		evt->crq.valid = 0x80;
>> +		evt->crq.valid = VIOSRP_CRQ_VALID;
>>   		evt->crq.IU_length = cpu_to_be16(sizeof(*evt->xfer_iu));
>>   		evt->crq.IU_data_ptr = cpu_to_be64(pool->iu_token +
>>   			sizeof(*evt->xfer_iu) * i);
>> @@ -1767,7 +1767,7 @@ static void ibmvscsi_handle_crq(struct viosrp_crq *crq,
>>   	struct srp_event_struct *evt_struct =
>>   			(__force struct srp_event_struct *)crq->IU_data_ptr;
>>   	switch (crq->valid) {
>> -	case 0xC0:		/* initialization */
>> +	case VIOSRP_CRQ_INIT:		/* initialization */
>>   		switch (crq->format) {
>>   		case 0x01:	/* Initialization message */
>>   			dev_info(hostdata->dev, "partner initialized\n");
>> @@ -1791,7 +1791,7 @@ static void ibmvscsi_handle_crq(struct viosrp_crq *crq,
>>   			dev_err(hostdata->dev, "unknown crq message type: %d\n", crq->format);
>>   		}
>>   		return;
>> -	case 0xFF:	/* Hypervisor telling us the connection is closed */
>> +	case VIOSRP_CRQ_TRANSPORT:	/* Hypervisor telling us the connection is closed */
>>   		scsi_block_requests(hostdata->host);
>>   		atomic_set(&hostdata->request_limit, 0);
>>   		if (crq->format == 0x06) {
>> @@ -1807,7 +1807,7 @@ static void ibmvscsi_handle_crq(struct viosrp_crq *crq,
>>   			ibmvscsi_reset_host(hostdata);
>>   		}
>>   		return;
>> -	case 0x80:		/* real payload */
>> +	case VIOSRP_CRQ_VALID:		/* real payload */
>>   		break;
>>   	default:
>>   		dev_err(hostdata->dev, "got an invalid message type 0x%02x\n",
>> diff --git a/drivers/scsi/ibmvscsi/viosrp.h b/drivers/scsi/ibmvscsi/viosrp.h
>> index d1044e9..17f2de0 100644
>> --- a/drivers/scsi/ibmvscsi/viosrp.h
>> +++ b/drivers/scsi/ibmvscsi/viosrp.h
>> @@ -51,6 +51,13 @@ union srp_iu {
>>   	u8 reserved[SRP_MAX_IU_LEN];
>>   };
>>
>> +enum viosrp_crq_headers {
>> +	VIOSRP_CRQ_FREE = 0x00,
>> +	VIOSRP_CRQ_VALID = 0x80,
>> +	VIOSRP_CRQ_INIT = 0xC0,
>> +	VIOSRP_CRQ_TRANSPORT = 0xFF
>> +};
>> +
>>   enum viosrp_crq_formats {
>>   	VIOSRP_SRP_FORMAT = 0x01,
>>   	VIOSRP_MAD_FORMAT = 0x02,
>>
> 
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