[PATCH net 02/10] ice: fix VF queue configuration with low MTU values

[Tony Nguyen <anthony.l.nguyen@intel.com>]

From: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>

The ice driver's VF queue configuration validation rejects
databuffer_size values below 1024 bytes, which prevents VFs from
using MTU values below 871 bytes.

The iavf driver calculates databuffer_size based on the MTU using:
  databuffer_size = ALIGN(MTU + LIBETH_RX_LL_LEN, 128)

where LIBETH_RX_LL_LEN = 26 (ETH_HLEN + 2*VLAN_HLEN + ETH_FCS_LEN).

For MTU values below 871:
  MTU 870: 870 + 26 = 896, aligned to 128 = 896 (< 1024, rejected)
  MTU 871: 871 + 26 = 897, aligned to 128 = 1024 (>= 1024, accepted)

The 1024-byte minimum seems unnecessarily restrictive, because the hardware
supports databuffer_size as low as 128 bytes (the alignment boundary),
which should allow MTU values down to the standard minimum of 68 bytes.

I haven't found the reason why the limit was configured in the commit
9c7dd7566d18 ("ice: add validation in OP_CONFIG_VSI_QUEUES VF message"), so
with no more information and since it is working, change the minimum
databuffer_size validation from 1024 to 128 bytes to allow standard low
MTU values while still preventing invalid configurations.

Fixes: 9c7dd7566d18 ("ice: add validation in OP_CONFIG_VSI_QUEUES VF message")
cc: stable@vger.kernel.org
Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
---
 drivers/net/ethernet/intel/ice/virt/queues.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/ice/virt/queues.c b/drivers/net/ethernet/intel/ice/virt/queues.c
index f73d5a3e83d4..31be2f76181c 100644
--- a/drivers/net/ethernet/intel/ice/virt/queues.c
+++ b/drivers/net/ethernet/intel/ice/virt/queues.c
@@ -840,7 +840,7 @@ int ice_vc_cfg_qs_msg(struct ice_vf *vf, u8 *msg)
 
 			if (qpi->rxq.databuffer_size != 0 &&
 			    (qpi->rxq.databuffer_size > ((16 * 1024) - 128) ||
-			     qpi->rxq.databuffer_size < 1024))
+			     qpi->rxq.databuffer_size < 128))
 				goto error_param;
 
 			ring->rx_buf_len = qpi->rxq.databuffer_size;
-- 
2.47.1