net: ethtool: fix ethtool_ringparam_get_cfg() returns a hds_thresh value always as 0.

JIRA: https://issues.redhat.com/browse/RHEL-75603

commit 216a61d
Author: Taehee Yoo <ap420073@gmail.com>
Date:   Fri Apr 4 12:21:25 2025 +0000

    net: ethtool: fix ethtool_ringparam_get_cfg() returns a hds_thresh value always as 0.

    When hds-thresh is configured, ethnl_set_rings() is called, and it calls
    ethtool_ringparam_get_cfg() to get ringparameters from .get_ringparam()
    callback and dev->cfg.
    Both hds_config and hds_thresh values should be set from dev->cfg, not
    from .get_ringparam().
    But ethtool_ringparam_get_cfg() sets only hds_config from dev->cfg.
    So, ethtool_ringparam_get_cfg() returns always a hds_thresh as 0.

    If an input value of hds-thresh is 0, a hds_thresh value from
    ethtool_ringparam_get_cfg() are same. So ethnl_set_rings() does
    nothing and returns immediately.
    It causes a bug that setting a hds-thresh value to 0 is not working.

    Reproducer:
        modprobe netdevsim
        echo 1 > /sys/bus/netdevsim/new_device
        ethtool -G eth0 hds-thresh 100
        ethtool -G eth0 hds-thresh 0
        ethtool -g eth0
        #hds-thresh value should be 0, but it shows 100.

    The tools/testing/selftests/drivers/net/hds.py can test it too with
    applying a following patch for hds.py.

    Fixes: 928459b ("net: ethtool: populate the default HDS params in the core")
    Signed-off-by: Taehee Yoo <ap420073@gmail.com>
    Link: https://patch.msgid.link/20250404122126.1555648-2-ap420073@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Mohammad Heib <mheib@redhat.com>

Author: mohammadheib

net/ethtool/common.c

@@ -828,6 +828,7 @@ void ethtool_ringparam_get_cfg(struct net_device *dev,
 
 	/* Driver gives us current state, we want to return current config */
 	kparam->tcp_data_split = dev->cfg->hds_config;
+	kparam->hds_thresh = dev->cfg->hds_thresh;
 }
 
 static void ethtool_init_tsinfo(struct kernel_ethtool_ts_info *info)