Re: [Enable Designware XGMAC VLAN Stripping Feature 2/2] net: stmmac: dwxgmac2: Add support for HW-accelerated VLAN Stripping

[Florian Fainelli]

On 7/21/2023 8:30 AM, Ng, Boon Khai wrote:
> > -----Original Message-----
> > From: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
> > Sent: Friday, July 21, 2023 6:11 PM
> > To: Boon@xxxxxxxxxxxxxxxxxxxx; Khai@xxxxxxxxxxxxxxxxxxxx; "Ng
> > <boon.khai.ng"@intel.com; Giuseppe Cavallaro <peppe.cavallaro@xxxxxx>;
> > Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>; Jose Abreu
> > <joabreu@xxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Eric
> > Dumazet <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>;
> > Paolo Abeni <pabeni@xxxxxxxxxx>; Maxime Coquelin
> > <mcoquelin.stm32@xxxxxxxxx>; netdev@xxxxxxxxxxxxxxx; linux-stm32@st-
> > md-mailman.stormreply.com; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> > kernel@xxxxxxxxxxxxxxx
> > Cc: Ng, Boon Khai <boon.khai.ng@xxxxxxxxx>; Shevchenko, Andriy
> > <andriy.shevchenko@xxxxxxxxx>; Tham, Mun Yew
> > <mun.yew.tham@xxxxxxxxx>; Swee, Leong Ching
> > <leong.ching.swee@xxxxxxxxx>; G Thomas, Rohan
> > <rohan.g.thomas@xxxxxxxxx>; Shevchenko Andriy
> > <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > 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@xxxxxxxxxxxxxxxxxxxx wrote:
> > > From: Boon Khai Ng <boon.khai.ng@xxxxxxxxx>
> > >
> > > 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