linux-kernel - RE: [RFC,net-next,v1, 1/1] net: stmmac: Enable SERDES power up/down sequence

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Date:   Mon, 23 Mar 2020 08:53:28 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     "Voon, Weifeng" <weifeng.voon@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Giuseppe Cavallaro" <peppe.cavallaro@...com>,
        Andrew Lunn <andrew@...n.ch>,
        Alexandre Torgue <alexandre.torgue@...com>,
        "Ong, Boon Leong" <boon.leong.ong@...el.com>
Subject: RE: [RFC,net-next,v1, 1/1] net: stmmac: Enable SERDES power up/down
 sequence

From: Voon, Weifeng <weifeng.voon@...el.com>
Date: Mar/23/2020, 08:16:29 (UTC+00:00)

> > > This patch is to enable Intel SERDES power up/down sequence. The
> > > SERDES converts 8/10 bits data to SGMII signal. Below is an example of
> > > HW configuration for SGMII mode. The SERDES is located in the PHY IF
> > > in the diagram below.
> > >
> > > <-----------------GBE Controller---------->|<--External PHY chip-->
> > > +----------+         +----+            +---+           +----------+
> > > |   EQoS   | <-GMII->| DW | < ------ > |PHY| <-SGMII-> | External |
> > > |   MAC    |         |xPCS|            |IF |           | PHY      |
> > > +----------+         +----+            +---+           +----------+
> > >        ^               ^                 ^                ^
> > >        |               |                 |                |
> > >        +---------------------MDIO-------------------------+
> > >
> > > PHY IF configuration and status registers are accessible through mdio
> > > address 0x15 which is defined as intel_adhoc_addr. During D0, The
> > > driver will need to power up PHY IF by changing the power state to P0.
> > > Likewise, for D3, the driver sets PHY IF power state to P3.
> > 
> > I don't think this is the right approach.
> > 
> > You could just add a new "mdio-intel-serdes" to phy/ folder just like I
> > did with XPCS because this is mostly related with PHY settings rather
> > than EQoS.
> I am taking this approach to put it in stmmac folder rather than phy folder
> as a generic mdio-intel-serdes as this is a specific Intel serdes architecture which
> would only pair with DW EQos and DW xPCS HW. Since this serdes will not able to
> pair other MAC or other non-Intel platform, I would like you to reconsider this
> approach. I am open for discussion. 
> Thanks Jose for the fast response.

OK, then I think we should use the BSP init/exit functions that are 
already available for platform setups (.init and .exit callback of 
plat_stmmacenet_data struct). We just need to extend this to PCI based 
setups.

You can take a look at stmmac_platform.c and check what's done. 
Basically:
	- Call priv->plat->init() at probe() and resume()
	- Call priv->plat->exit() at remove() and suspend()

---
Thanks,
Jose Miguel Abreu