RE: [PATCH v2] IGC: Remove I225_I_PHY_ID checking

["Mah, Yock Gen" <yock.gen.mah@intel.com>]

-----Original Message-----
From: Kevin Traynor <ktraynor@redhat.com> 
Sent: Tuesday, 18 October, 2022 8:54 PM
To: Mah, Yock Gen <yock.gen.mah@intel.com>; IOTG DPDK Ref App <iotg.dpdk.ref.app@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>
Cc: dev@dpdk.org
Subject: Re: [PATCH v2] IGC: Remove I225_I_PHY_ID checking

On 12/10/2022 09:39, Kevin Traynor wrote:
> On 12/10/2022 08:45, Mah, Yock Gen wrote:
>>
>>
>> -----Original Message-----
>> From: Kevin Traynor <ktraynor@redhat.com>
>> Sent: Tuesday, 11 October, 2022 7:05 PM
>> To: IOTG DPDK Ref App <iotg.dpdk.ref.app@intel.com>; Zhang, Qi Z 
>> <qi.z.zhang@intel.com>
>> Cc: dev@dpdk.org
>> Subject: Re: [PATCH v2] IGC: Remove I225_I_PHY_ID checking
>>
>> On 31/08/2022 23:51, iotg.dpdk.ref.app@intel.com wrote:
>>> From: NSWE SWS DPDK Dev <iotg.dpdk.ref.app@intel.com>
>>>
>>> i225 devices have only one PHY vendor. There is unnecessary to check 
>>> _I_PHY_ID during the link establishment and auto-negotiation 
>>> process, the checking also caused devices like i225-IT failed. This 
>>> patch is to remove the mentioned unnecessary checking.
>>>
>>> Cc: stable@dpdk.org
>>> Signed-off-by: NSWE SWS DPDK Dev <iotg.dpdk.ref.app@intel.com>
>>> ---
>>>     drivers/net/igc/base/igc_i225.c | 15 ++-------------
>>>     drivers/net/igc/base/igc_phy.c  |  6 ++----
>>>     2 files changed, 4 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/net/igc/base/igc_i225.c 
>>> b/drivers/net/igc/base/igc_i225.c index 5f3d535490..af26602afb 
>>> 100644
>>> --- a/drivers/net/igc/base/igc_i225.c
>>> +++ b/drivers/net/igc/base/igc_i225.c
>>> @@ -173,19 +173,8 @@ static s32 igc_init_phy_params_i225(struct igc_hw *hw)
>>>     	phy->ops.write_reg = igc_write_phy_reg_gpy;
>>>     
>>>     	ret_val = igc_get_phy_id(hw);
>>> -	/* Verify phy id and set remaining function pointers */
>>> -	switch (phy->id) {
>>> -	case I225_I_PHY_ID:
>>> -	case I226_LM_PHY_ID:
>>> -		phy->type		= igc_phy_i225;
>>> -		phy->ops.set_d0_lplu_state = igc_set_d0_lplu_state_i225;
>>> -		phy->ops.set_d3_lplu_state = igc_set_d3_lplu_state_i225;
>>
>>> - The commit log says it is removing a check on the ID, but it does not say why these function pointers are being removed.
>>
>>> - Why are they removed, were they not needed?
>>
>>
>> i225 devices have only one PHY vendor. There is no point checking _I_PHY_ID during the link establishment and auto-negotiation process.
>>
> 
> Right, that's clear about the vendor ID check. But it's not clear to 
> me why the the resulting code like this:
> 
> phy->type = igc_phy_i225;
> 
>    and not like this:
> 
> phy->type = igc_phy_i225;
> phy->ops.set_d0_lplu_state = igc_set_d0_lplu_state_i225; 
> phy->ops.set_d3_lplu_state = igc_set_d3_lplu_state_i225;
> 
> So it is using dummy null functions instead:
> https://git.dpdk.org/dpdk/tree/drivers/net/igc/base/igc_phy.c#n61
> 
> Do the device registers not need to be set anymore?
> 

> For main branch, it would be nice to have an answer to above.

> It only adds a small readability benefit by removing some code branches, but does change functionality which adds risk, so I don't think it's a good candidate for stable branches.

This is not only added readability, but to fix real world issue, we were experiencing i225-IT not runnable issue without patching another case checking as below:

+++ b/drivers/net/igc/base/igc_phy.c
@@ -1881,6 +1881,7 @@ s32 igc_phy_force_speed_duplex_m88(struct igc_hw *hw)
                                case I210_I_PHY_ID:
                                /* fall-through */
                                case I225_I_PHY_ID:
+                              case I225_IT_PHY_ID:

However, cleaner solution is to remove those unnecessary checking completely as it does in kernel also https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c496de538eebd8212dc2a3c9a468386b264d0d4

>>> -		/* TODO - complete with GPY PHY information */
>>> -		break;
>>> -	default:
>>> -		ret_val = -IGC_ERR_PHY;
>>> -		goto out;
>>> -	}
>>> +        phy->type = igc_phy_i225;
>>> +
>>>     
>>>     out:
>>>     	return ret_val;
>>> diff --git a/drivers/net/igc/base/igc_phy.c 
>>> b/drivers/net/igc/base/igc_phy.c index 43bbe69bca..2906bae21a 100644
>>> --- a/drivers/net/igc/base/igc_phy.c
>>> +++ b/drivers/net/igc/base/igc_phy.c
>>> @@ -1474,8 +1474,7 @@ s32 igc_phy_setup_autoneg(struct igc_hw *hw)
>>>     			return ret_val;
>>>     	}
>>>     
>>> -	if ((phy->autoneg_mask & ADVERTISE_2500_FULL) &&
>>> -	    hw->phy.id == I225_I_PHY_ID) {
>>> +	if (phy->autoneg_mask & ADVERTISE_2500_FULL) {
>>>     	/* Read the MULTI GBT AN Control Register - reg 7.32 */
>>>     		ret_val = phy->ops.read_reg(hw, (STANDARD_AN_REG_MASK <<
>>>     					    MMD_DEVADDR_SHIFT) |
>>> @@ -1615,8 +1614,7 @@ s32 igc_phy_setup_autoneg(struct igc_hw *hw)
>>>     		ret_val = phy->ops.write_reg(hw, PHY_1000T_CTRL,
>>>     					     mii_1000t_ctrl_reg);
>>>     
>>> -	if ((phy->autoneg_mask & ADVERTISE_2500_FULL) &&
>>> -	    hw->phy.id == I225_I_PHY_ID)
>>> +	if (phy->autoneg_mask & ADVERTISE_2500_FULL)
>>>     		ret_val = phy->ops.write_reg(hw,
>>>     					     (STANDARD_AN_REG_MASK <<
>>>     					     MMD_DEVADDR_SHIFT) |
>>
>