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Date:   Fri, 21 Jul 2023 08:59:06 -0700
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Subject: Re: [Enable Designware XGMAC VLAN Stripping Feature 2/2] net: stmmac:
 dwxgmac2: Add support for HW-accelerated VLAN Stripping
Content-Language: en-US
To:     "Ng, Boon Khai" <boon.khai.ng@intel.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        "Boon@ecsmtp.png.intel.com" <Boon@ecsmtp.png.intel.com>,
        "Khai@ecsmtp.png.intel.com" <Khai@ecsmtp.png.intel.com>,
        boon.khai.ng@intel.com,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        Jose Abreu <joabreu@synopsys.com>,
        "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-stm32@st-md-mailman.stormreply.com" 
        <linux-stm32@st-md-mailman.stormreply.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc:     "Shevchenko, Andriy" <andriy.shevchenko@intel.com>,
        "Tham, Mun Yew" <mun.yew.tham@intel.com>,
        "Swee, Leong Ching" <leong.ching.swee@intel.com>,
        "G Thomas, Rohan" <rohan.g.thomas@intel.com>,
        Shevchenko Andriy <andriy.shevchenko@linux.intel.com>
References: <20230721062617.9810-1-boon.khai.ng@intel.com>
 <20230721062617.9810-3-boon.khai.ng@intel.com>
 <cfba8fa4-47e5-7553-f40e-9e34b25d1405@kernel.org>
 <DM8PR11MB5751E5388AEFCFB80BCB483FC13FA@DM8PR11MB5751.namprd11.prod.outlook.com>
From:   Florian Fainelli <f.fainelli@gmail.com>
In-Reply-To: <DM8PR11MB5751E5388AEFCFB80BCB483FC13FA@DM8PR11MB5751.namprd11.prod.outlook.com>
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On 7/21/2023 8:30 AM, Ng, Boon Khai wrote:
>> -----Original Message-----
>> From: Krzysztof Kozlowski <krzk@kernel.org>
>> Sent: Friday, July 21, 2023 6:11 PM
>> To: Boon@ecsmtp.png.intel.com; Khai@ecsmtp.png.intel.com; "Ng
>> <boon.khai.ng"@intel.com; Giuseppe Cavallaro <peppe.cavallaro@st.com>;
>> Alexandre Torgue <alexandre.torgue@foss.st.com>; Jose Abreu
>> <joabreu@synopsys.com>; David S . Miller <davem@davemloft.net>; Eric
>> Dumazet <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>;
>> Paolo Abeni <pabeni@redhat.com>; Maxime Coquelin
>> <mcoquelin.stm32@gmail.com>; netdev@vger.kernel.org; linux-stm32@st-
>> md-mailman.stormreply.com; linux-arm-kernel@lists.infradead.org; linux-
>> kernel@vger.kernel.org
>> Cc: Ng, Boon Khai <boon.khai.ng@intel.com>; Shevchenko, Andriy
>> <andriy.shevchenko@intel.com>; Tham, Mun Yew
>> <mun.yew.tham@intel.com>; Swee, Leong Ching
>> <leong.ching.swee@intel.com>; G Thomas, Rohan
>> <rohan.g.thomas@intel.com>; Shevchenko Andriy
>> <andriy.shevchenko@linux.intel.com>
>> Subject: Re: [Enable Designware XGMAC VLAN Stripping Feature 2/2] net:
>> stmmac: dwxgmac2: Add support for HW-accelerated VLAN Stripping
>>
>> On 21/07/2023 08:26, Boon@ecsmtp.png.intel.com wrote:
>>> From: Boon Khai Ng <boon.khai.ng@intel.com>
>>>
>>> Currently, VLAN tag stripping is done by software driver in
>>> stmmac_rx_vlan(). This patch is to Add support for VLAN tag stripping
>>> by the MAC hardware and MAC drivers to support it.
>>> This is done by adding rx_hw_vlan() and set_hw_vlan_mode() callbacks
>>> at stmmac_ops struct which are called from upper software layer.
>> ...
>>
>>>   	if (priv->dma_cap.vlhash) {
>>>   		ndev->features |= NETIF_F_HW_VLAN_CTAG_FILTER;
>>>   		ndev->features |= NETIF_F_HW_VLAN_STAG_FILTER; diff --
>> git
>>> a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>> b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>> index 23d53ea04b24..bd7f3326a44c 100644
>>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>> @@ -543,6 +543,12 @@ stmmac_probe_config_dt(struct platform_device
>> *pdev, u8 *mac)
>>>   			plat->flags |= STMMAC_FLAG_TSO_EN;
>>>   	}
>>>
>>> +	/* Rx VLAN HW Stripping */
>>> +	if (of_property_read_bool(np, "snps,rx-vlan-offload")) {
>>> +		dev_info(&pdev->dev, "RX VLAN HW Stripping\n");
>>
>> Why? Drop.
>>
> 
> This is an dts option export to dts for user to choose whether or not they
> Want a Hardware stripping or a software stripping.
> 
> May I know what is the reason to drop this?

Because the networking stack already exposes knobs for drivers to 
advertise and control VLAN stripping/insertion on RX/TX using ethtool 
and feature bits (NETIF_F_HW_VLAN_CTAG_RX, NETIF_F_HW_VLAN_CTAG_TX).

What you are doing here is encode a policy as a Device Tree property 
rather than describe whether the hardware supports a given feature and 
this is frowned upon.
-- 
Florian