netdev - Re: [PATCH net-next v8 2/6] net: pcs: xpcs: re-initiate clause 37 Auto-negotiation

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Message-ID: <55ddacb9-dc00-4477-aeab-9b8861563194@linux.intel.com>
Date: Thu, 27 Feb 2025 19:18:02 +0800
From: Choong Yong Liang <yong.liang.choong@...ux.intel.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Simon Horman <horms@...nel.org>, Jose Abreu <joabreu@...opsys.com>,
 Jose Abreu <Jose.Abreu@...opsys.com>,
 David E Box <david.e.box@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H . Peter Anvin" <hpa@...or.com>,
 Rajneesh Bhardwaj <irenic.rajneesh@...il.com>,
 David E Box <david.e.box@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Maxime Coquelin
 <mcoquelin.stm32@...il.com>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>, Jiawen Wu <jiawenwu@...stnetic.com>,
 Mengyuan Lou <mengyuanlou@...-swift.com>,
 Heiner Kallweit <hkallweit1@...il.com>, Hans de Goede <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Richard Cochran <richardcochran@...il.com>,
 Serge Semin <fancer.lancer@...il.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 platform-driver-x86@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net-next v8 2/6] net: pcs: xpcs: re-initiate clause 37
 Auto-negotiation

On 26/2/2025 11:40 pm, Russell King (Oracle) wrote:
> On Wed, Feb 26, 2025 at 03:48:33PM +0800, Choong Yong Liang wrote:
>> diff --git a/drivers/net/pcs/pcs-xpcs-wx.c b/drivers/net/pcs/pcs-xpcs-wx.c
>> index fc52f7aa5f59..f73ab04d09f0 100644
>> --- a/drivers/net/pcs/pcs-xpcs-wx.c
>> +++ b/drivers/net/pcs/pcs-xpcs-wx.c
>> @@ -172,11 +172,9 @@ int txgbe_xpcs_switch_mode(struct dw_xpcs *xpcs, phy_interface_t interface)
>>   		return 0;
>>   	}
>>   
>> -	if (xpcs->interface == interface && !txgbe_xpcs_mode_quirk(xpcs))
>> +	if (!txgbe_xpcs_mode_quirk(xpcs))
>>   		return 0;
>>   
>> -	xpcs->interface = interface;
>> -
> 
> ...
> 
>> --- a/drivers/net/pcs/pcs-xpcs.c
>> +++ b/drivers/net/pcs/pcs-xpcs.c
>> @@ -602,12 +602,37 @@ static void xpcs_get_interfaces(struct dw_xpcs *xpcs, unsigned long *interfaces)
>>   		__set_bit(compat->interface, interfaces);
>>   }
>>   
>> +static int xpcs_switch_interface_mode(struct dw_xpcs *xpcs,
>> +				      phy_interface_t interface)
>> +{
>> +	int ret = 0;
>> +
>> +	if (xpcs->interface != interface) {
>> +		if (xpcs->info.pma == WX_TXGBE_XPCS_PMA_10G_ID) {
>> +			ret = txgbe_xpcs_switch_mode(xpcs, interface);
>> +			if (ret)
>> +				return ret;
> 
> The above modification changes the functionality.
> 
> In the old code, txgbe_xpcs_switch_mode() does its work when
> xpcs->interface is not the same as interface OR txgbe_xpcs_mode_quirk()
> is true.
> 
> Your replacement code calls txgbe_xpcs_switch_mode() when
> xpcs->interface is not the same as interface, *and* it can do its
> work when txgbe_xpcs_mode_quirk() returns true.
> 
> So, e.g. when txgbe_xpcs_mode_quirk() returns false, but the interface
> changes, txgbe_xpcs_mode_quirk() used to do its work, but as a result
> if your changes, it becomes a no-op.
> 
> The point of txgbe_xpcs_mode_quirk() is to always do the work if it
> returns true, even if the interface mode doesn't change.
> 
> Therefore, this patch is logically incorrect, and likely breaks TXGBE.
> 
Thank you for pointing out the oversight. I will review the logic and make 
the necessary corrections to ensure the patch does not disrupt the expected 
behavior.