netdev - Re: [PATCH net-next 3/5] net: bcmasp: Add support for ASP2.0 Ethernet controller

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Message-ID: <YVB8ef3aMpJTEvgF@lunn.ch>
Date:   Sun, 26 Sep 2021 15:58:17 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Justin Chen <justinpopo6@...il.com>, netdev@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Doug Berger <opendmb@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Rafał Miłecki <rafal@...ecki.pl>,
        Randy Dunlap <rdunlap@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Michael Chan <michael.chan@...adcom.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH net-next 3/5] net: bcmasp: Add support for ASP2.0
 Ethernet controller

> > > +static int bcmasp_set_priv_flags(struct net_device *dev, u32 flags)
> > > +{
> > > +	struct bcmasp_intf *intf = netdev_priv(dev);
> > > +
> > > +	intf->wol_keep_rx_en = flags & BCMASP_WOL_KEEP_RX_EN ? 1 : 0;
> > > +
> > > +	return 0;
> > 
> > Please could you explain this some more. How can you disable RX and
> > still have WoL working?
> 
> Wake-on-LAN using Magic Packets and network filters requires keeping the
> UniMAC's receiver turned on, and then the packets feed into the Magic Packet
> Detector (MPD) block or the network filter block. In that mode DRAM is in
> self refresh and there is local matching of frames into a tiny FIFO however
> in the case of magic packets the packets leading to a wake-up are dropped as
> there is nowhere to store them. In the case of a network filter match (e.g.:
> matching a multicast IP address plus protocol, plus source/destination
> ports) the packets are also discarded because the receive DMA was shut down.
> 
> When the wol_keep_rx_en flag is set, the above happens but we also allow the
> packets that did match a network filter to reach the small FIFO (Justin
> would know how many entries are there) that is used to push the packets to
> DRAM. The packet contents are held in there until the system wakes up which
> is usually just a few hundreds of micro seconds after we received a packet
> that triggered a wake-up. Once we overflow the receive DMA FIFO capacity
> subsequent packets get dropped which is fine since we are usually talking
> about very low bit rates, and we only try to push to DRAM the packets of
> interest, that is those for which we have a network filter.
> 
> This is convenient in scenarios where you want to wake-up from multicast DNS
> (e.g.: wake on Googlecast, Bonjour etc.) because then the packet that
> resulted in the system wake-up is not discarded but is then delivered to the
> network stack.

Thanks for the explanation. It would be easier for the user if you
automate this. Enable is by default for WoL types which have user
content?

> > > +	/* Per ch */
> > > +	intf->tx_spb_dma = priv->base + TX_SPB_DMA_OFFSET(intf);
> > > +	intf->res.tx_spb_ctrl = priv->base + TX_SPB_CTRL_OFFSET(intf);
> > > +	/*
> > > +	 * Stop gap solution. This should be removed when 72165a0 is
> > > +	 * deprecated
> > > +	 */
> > 
> > Is that an internal commit?
> 
> Yes this is a revision of the silicon that is not meant to see the light of
> day.

So this can all be removed?

   Andrew