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From: Prasanna Vengateshan <prasanna.vengateshan@microchip.com>
To: Vladimir Oltean <olteanv@gmail.com>, Andrew Lunn <andrew@lunn.ch>
Cc: <netdev@vger.kernel.org>, <robh+dt@kernel.org>,
	<UNGLinuxDriver@microchip.com>, <Woojung.Huh@microchip.com>,
	<hkallweit1@gmail.com>, <linux@armlinux.org.uk>,
	<davem@davemloft.net>, <kuba@kernel.org>,
	<linux-kernel@vger.kernel.org>, <vivien.didelot@gmail.com>,
	<f.fainelli@gmail.com>, <devicetree@vger.kernel.org>
Subject: Re: [PATCH v3 net-next 05/10] net: dsa: microchip: add DSA support for microchip lan937x
Date: Tue, 3 Aug 2021 22:24:27 +0530	[thread overview]
Message-ID: <50eb24a1e407b651eda7aeeff26d82d3805a6a41.camel@microchip.com> (raw)
In-Reply-To: <20210802135911.inpu6khavvwsfjsp@skbuf>

On Mon, 2021-08-02 at 16:59 +0300, Vladimir Oltean wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
> content is safe
> 
> On Mon, Aug 02, 2021 at 03:13:01PM +0200, Andrew Lunn wrote:
> > In general, the MAC does nothing, and passes the value to the PHY. The
> > PHY inserts delays as requested. To address Vladimir point,
> > PHY_INTERFACE_MODE_RGMII_TXID would mean the PHY adds delay in the TX
> > direction, and assumes the RX delay comes from somewhere else,
> > probably the PCB.
> 
> For the PHY, that is the only portion where things are clear.
> 
> > I only recommend the MAC adds delays when the PHY cannot, or there is
> > no PHY, e.g. SoC to switch, or switch to switch link. There are a few
> > MAC drivers that do add delays, mostly because that is how the vendor
> > crap tree does it.
> > 
> > So as i said, what you propose is O.K, it follows this general rule of
> > thumb.
> 
> The "rule of thumb" for a MAC driver is actually applied in reverse by
> most MAC drivers compared to what Russell described should be happening.
> For example, mv88e6xxx_port_set_rgmii_delay():
> 
>         switch (mode) {
>         case PHY_INTERFACE_MODE_RGMII_RXID:
>                 reg |= MV88E6XXX_PORT_MAC_CTL_RGMII_DELAY_RXCLK;
> 
> The mv88e6xxx is a MAC, so when it has a phy-mode = "rgmii-rxid", it
> should assume it is connected to a link partner (PHY or otherwise) that
> has applied the RXCLK delay already. So it should only be concerned with
> the TXCLK delay. That is my point. I am just trying to lay out the
> points to Prasanna that would make a sane system going forward. I am not
> sure that we actually have an in-tree driver that is sane in that
> regard.
> 
> That discussion, and Russell's point, was here, btw:
> https://patchwork.ozlabs.org/project/netdev/patch/20200616074955.GA9092@laureti-dev/#2461123

Thanks Vladimir & Andrew for the right pointers and info. The thread talks about
"rgmii-*" are going to be applied by the PHY only as per the doc. For fixed-
link, MAC needs to add the delay. This fixed-link can be No-PHY or MAC-MAC or
MAC to in-accessible PHY. In such case, i am not convinced in using rgmii-tx-
delay-ps & rgmii-rx-delay-ps on the MAC side and apply delay. I still think
proposed code in earlier mail thread should still be okay. 


  parent reply	other threads:[~2021-08-03 16:54 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-23 17:30 [PATCH v3 net-next 00/10] net: dsa: microchip: DSA driver support for LAN937x switch Prasanna Vengateshan
2021-07-23 17:30 ` [PATCH v3 net-next 01/10] dt-bindings: net: dsa: dt bindings for microchip lan937x Prasanna Vengateshan
2021-07-26 22:49   ` Rob Herring
2021-07-23 17:31 ` [PATCH v3 net-next 02/10] net: dsa: move mib->cnt_ptr reset code to ksz_common.c Prasanna Vengateshan
2021-07-23 18:53   ` Vladimir Oltean
2021-07-23 17:31 ` [PATCH v3 net-next 03/10] net: phy: Add support for LAN937x T1 phy driver Prasanna Vengateshan
2021-08-11 17:52   ` Prasanna Vengateshan
2021-07-23 17:31 ` [PATCH v3 net-next 04/10] net: dsa: tag_ksz: add tag handling for Microchip LAN937x Prasanna Vengateshan
2021-07-23 19:23   ` Vladimir Oltean
2021-07-23 17:31 ` [PATCH v3 net-next 05/10] net: dsa: microchip: add DSA support for microchip lan937x Prasanna Vengateshan
2021-07-31 15:04   ` Vladimir Oltean
2021-07-31 22:05     ` Andrew Lunn
2021-08-02 21:33       ` Vladimir Oltean
2021-08-03 14:43         ` Andrew Lunn
2021-08-03 15:05           ` Vladimir Oltean
2021-08-02 10:45     ` Prasanna Vengateshan
2021-08-02 12:15       ` Vladimir Oltean
2021-08-02 13:13         ` Andrew Lunn
2021-08-02 13:59           ` Vladimir Oltean
2021-08-02 20:47             ` Andrew Lunn
2021-08-03 16:54             ` Prasanna Vengateshan [this message]
2021-08-03 23:54               ` Vladimir Oltean
2021-08-04  9:59                 ` Russell King (Oracle)
2021-08-04 10:46                   ` Vladimir Oltean
2021-08-04 14:28                     ` Prasanna Vengateshan
2021-08-04 14:51                       ` Vladimir Oltean
2021-08-07 15:40                     ` Andrew Lunn
2021-08-07 17:00                       ` Vladimir Oltean
2021-08-11 17:44                       ` Prasanna Vengateshan
2021-08-11 18:23                         ` Andrew Lunn
2021-08-11 20:14                           ` Russell King (Oracle)
2021-08-11 20:20                             ` Vladimir Oltean
2021-08-11 20:22                               ` Andrew Lunn
2021-07-23 17:31 ` [PATCH v3 net-next 06/10] net: dsa: microchip: add support for phylink management Prasanna Vengateshan
2021-07-31 15:27   ` Vladimir Oltean
2021-08-03 17:04     ` Prasanna Vengateshan
2021-07-23 17:31 ` [PATCH v3 net-next 07/10] net: dsa: microchip: add support for ethtool port counters Prasanna Vengateshan
2021-07-23 17:31 ` [PATCH v3 net-next 08/10] net: dsa: microchip: add support for port mirror operations Prasanna Vengateshan
2021-07-31 15:24   ` Vladimir Oltean
2021-07-23 17:31 ` [PATCH v3 net-next 09/10] net: dsa: microchip: add support for fdb and mdb management Prasanna Vengateshan
2021-07-31 15:19   ` Vladimir Oltean
2021-07-23 17:31 ` [PATCH v3 net-next 10/10] net: dsa: microchip: add support for vlan operations Prasanna Vengateshan
2021-07-31 15:08   ` Vladimir Oltean
2021-08-02 10:48     ` Prasanna Vengateshan

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