[DPDK/ethdev Bug 1789] vmxnet3_dev_start fails in vmxnet3_v4_rss_configure() for single queue in ESX8.0 causing application to exit

[DPDK/ethdev Bug 1789] vmxnet3_dev_start fails in vmxnet3_v4_rss_configure() for single queue in ESX8.0 causing application to exit

[bugzilla]

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https://bugs.dpdk.org/show_bug.cgi?id=1789

            Bug ID: 1789
           Summary: vmxnet3_dev_start fails in vmxnet3_v4_rss_configure()
                    for single queue in ESX8.0 causing application to exit
           Product: DPDK
           Version: 19.11
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: ethdev
          Assignee: dev@dpdk.org
          Reporter: amiyaranjan.mohakud@gmail.com
  Target Milestone: ---

DPDK Version: 19.11
ESX version: ESX8.0

We faced an exact similar issue as mentioned in
https://mails.dpdk.org/archives/users/2025-April/008236.html. 

Context Details:
-----------------
In ESXi 8.0 setup with dpdk-19.11, when the HW compatibility version is ESX8.0
and with single queue pair configuration, the RSS gets enabled. As a result,
vmxnet3_v4_rss_configure() gets called and fails while writing/reading from
BAR1 hw register. It looks to be some compatibility issue with dpdk-19.11 and
ESX8.0.

        if (VMXNET3_VERSION_GE_4(hw) &&                                         
            dev->data->dev_conf.rxmode.mq_mode == ETH_MQ_RX_RSS) {              
                /* Check for additional RSS  */                                 
                ret = vmxnet3_v4_rss_configure(dev);                            
                if (ret != VMXNET3_SUCCESS) {                                   
                        PMD_INIT_LOG(ERR, "Failed to configure v4 RSS");        
                        return ret;                                             
                }                                                               
        }  

As a result, it causes the application to exit.

Proposed fix:
I have a plausible fix for this. The fix is to disable RSS for such a case (
the fix should go only in 19.11). During dev_configure(),  we can set the
mq_mode  to ETH_MQ_RX_NONE if the num_rx_queues is 1. This would avoid calling
of vmxnet3_v4_rss_configure().


        /* Disabling RSS for single queue pair */                               
        if (dev->data->nb_rx_queues == 1) {                                     
                dev->data->dev_conf.rxmode.mq_mode = ETH_MQ_RX_NONE;            
                PMD_INIT_LOG(ERR, "WARN: Disabling RSS for single Rx queue");   
        }


Pls verify and let me know if it can be upstreamed. Once confirmed/approved, If
required, I can generate a main stream patch for it.

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