netdev - Re: RE: [Intel-wired-lan] [PATCH v1 iwl-net] igc: power up PHY before link test

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Message-ID: <20250906040340.87510-1-enjuk@amazon.com>
Date: Sat, 6 Sep 2025 13:03:38 +0900
From: Kohei Enju <enjuk@...zon.com>
To: <aleksandr.loktionov@...el.com>
CC: <andrew+netdev@...n.ch>, <anthony.l.nguyen@...el.com>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <enjuk@...zon.com>,
	<intel-wired-lan@...ts.osuosl.org>, <kohei.enju@...il.com>,
	<kuba@...nel.org>, <netdev@...r.kernel.org>, <pabeni@...hat.com>,
	<przemyslaw.kitszel@...el.com>, <vitaly.lifshits@...el.com>
Subject: Re: RE: [Intel-wired-lan] [PATCH v1 iwl-net] igc: power up PHY before link test

On Mon, 1 Sep 2025 07:03:34 +0000, Loktionov, Aleksandr wrote:

[...]
>>  drivers/net/ethernet/intel/igc/igc_ethtool.c | 3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c
>> b/drivers/net/ethernet/intel/igc/igc_ethtool.c
>> index f3e7218ba6f3..ca93629b1d3a 100644
>> --- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
>> +++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c
>> @@ -2094,6 +2094,9 @@ static void igc_ethtool_diag_test(struct
>> net_device *netdev,
>>  		netdev_info(adapter->netdev, "Offline testing
>> starting");
>>  		set_bit(__IGC_TESTING, &adapter->state);
>> 
>> +		/* power up PHY for link test */
>> +		igc_power_up_phy_copper(&adapter->hw);
>> +
>1.You unconditionally power the PHY up but you don't restore the previous power state at the end of the test.

You're right about the concern, but it's already handled by the existing 
code flow:
    /* power up PHY for link test */
	igc_power_up_phy_copper(&adapter->hw);

    /* doing link test */

    if (if_running)
        igc_close(netdev);
    else
        igc_reset(adapter);
        
    /* other tests */
    igc_reset(adapter);

igc_reset() calls igc_power_down_phy_copper_base() when !netif_running(), 
so the PHY is properly powered down again.

>2. igc_power_up_phy_copper() returns a status, but you ignore it. If the MDIO access fails (e.g., bus issue), you should mark the link test as failed and continue with the rest...

Hmm, indeed I didn't check the status, but should I tweak `void
igc_power_up_phy_copper(struct igc_hw *hw)` itself?

My intention was to try to power up PHY if possible, but give it up when
not possible (e.g., bus issue). When powering up is not successful, that
is, PHY is still powered down, igc_link_test() should fail as it does so
now.

>n. igc is predominantly copper, but it's still best practice to guard with: 	if (hw->phy.media_type == igc_media_type_copper) or or check that hw->phy.type != igc_phy_none

Got it. I'll do that in v2.

>
>>  		/* Link test performed before hardware reset so autoneg
>> doesn't
>>  		 * interfere with test result
>>  		 */
>> --
>> 2.48.1