linux-kernel - Re: [PATCH net 2/2] net: pcs: xpcs: actively unset DW_VR_MII_DIG_CTRL1_2G5

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Message-ID: <Z4fXGULd-6_rxgRR@shell.armlinux.org.uk>
Date: Wed, 15 Jan 2025 15:41:13 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: netdev@...r.kernel.org, Jose Abreu <Jose.Abreu@...opsys.com>,
	Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Voon Weifeng <weifeng.voon@...el.com>,
	Michael Sit Wei Hong <michael.wei.hong.sit@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 2/2] net: pcs: xpcs: actively unset
 DW_VR_MII_DIG_CTRL1_2G5_EN for 1G SGMII

On Wed, Jan 15, 2025 at 04:51:45PM +0200, Vladimir Oltean wrote:
> On Wed, Jan 15, 2025 at 02:44:52PM +0000, Russell King (Oracle) wrote:
> > On Tue, Jan 14, 2025 at 06:47:21PM +0200, Vladimir Oltean wrote:
> > > xpcs_config_2500basex() sets DW_VR_MII_DIG_CTRL1_2G5_EN, but
> > > xpcs_config_aneg_c37_sgmii() never unsets it. So, on a protocol change
> > > from 2500base-x to sgmii, the DW_VR_MII_DIG_CTRL1_2G5_EN bit will remain
> > > set.
> > > 
> > > Fixes: f27abde3042a ("net: pcs: add 2500BASEX support for Intel mGbE controller")
> > > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> > 
> > Reviewed-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> > 
> > Thanks!
> > 
> > I wonder whether, now that we have in-band capabilities, and thus
> > phylink knows whether AN should be enabled or not, whether we can
> > simplify all these different config functions and rely on the
> > neg_mode from phylink to configure in-band appropriately.
> 
> I don't understand, many sub-functions of xpcs_do_config() use neg_mode
> already.
> 
> If you're talking about replacing compat->an_mode with something derived
> partially from the neg_mode and partially from state->interface, then in
> principle yes, sure, but we will need new neg_modes for clause 73
> auto-negotiation (to replace DW_AN_C73), plus appropriate handling in phylink.

No, I'm thinking that xpcs_config_aneg_c37_sgmii(),
xpcs_config_aneg_c37_1000basex() and xpcs_config_2500basex() can
be rolled into a single function.


	SGMII
	modify vendor 2 MII_BMCR
	- clear BMCR_ANENABLE
	modify vendor 2 DW_VR_MII_AN_CTRL
	- set DW_VR_MII_PCS_MODE_MASK to 
	  DW_VR_MII_PCS_MODE_C37_SGMII
	- configure  DW_VR_MII_TX_CONFIG_MASK for MAC or if txgbe, PHY side
	- set DW_VR_MII_AN_CTRL_8BIT (if txgbe)
	modify vendor 2 DW_VR_MII_DIG_CTRL1
	- set DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW if
	    PHYLINK_PCS_NEG_INBAND_ENABLED
	- set DW_VR_MII_DIG_CTRL1_PHY_MODE_CTRL if txgbe
	write vendor 2 DW_VR_MII_DIG_CTRL1
	set BMCR_ANENABLE in vendor 2 MII_BMCR if
	  PHYLINK_PCS_NEG_INBAND_ENABLED

	1000BASE-X
	modify vendor 2 MII_BMCR
	- clear BMCR_ANENABLE
	modify DW_VR_MII_AN_CTRL
	- set DW_VR_MII_PCS_MODE_MASK to
	  DW_VR_MII_PCS_MODE_C37_1000BASEX
	- set DW_VR_MII_AN_INTR_EN if using interrupts (shouldn't SGMII
	  also do this?)
	encode advertisement and write to vendor 2 MII_ADVERTISE
	clear vendor 2 DW_VR_MII_AN_INTR_STS register (if using
	interrupts shouldn't this also apply to SGMII?)
	set BMCR_ANENABLE in vendor 2 MII_BMCR if
	  PHYLINK_PCS_NEG_INBAND_ENABLED

	2500BASE-X
	modify vendor 2 DW_VR_MII_DIG_CTRL1:
	- set DW_VR_MII_DIG_CTRL1_2G5_EN
	- clear DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW
	modify vendor 2 MII_BMCR:
	- clear BMCR_ANENABLE, BMCR_SPEED100
	- set BMCR_SPEED1000
	(shouldn't this clear BMCR_ANENABLE first, like the other two
	 configurations above?)

So, sticking this altogether, making some assumptions on the above
questions, it becomes:

	modify vendor 2 MII_BMCR
	- clear BMCR_ANENABLE
	modify DW_VR_MII_AN_CTRL
	- set DW_VR_MII_PCS_MODE_MASK to 
	  - DW_VR_MII_PCS_MODE_C37_SGMII if using SGMII
	  - DW_VR_MII_PCS_MODE_C37_1000BASEX if using 1000BASE-X or
	    2500BASE-X
	- configure  DW_VR_MII_TX_CONFIG_MASK for MAC or if txgbe, PHY
	  side
	- set DW_VR_MII_AN_CTRL_8BIT (if txgbe)
	- set DW_VR_MII_AN_INTR_EN if using interrupts (shouldn't SGMII
	  also do this?)
	modify vendor 2 DW_VR_MII_DIG_CTRL1
	- set DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW if
	    PHYLINK_PCS_NEG_INBAND_ENABLED
	- set DW_VR_MII_DIG_CTRL1_PHY_MODE_CTRL if txgbe
	encode advertisement and write to vendor 2 MII_ADVERTISE
	clear vendor 2 DW_VR_MII_AN_INTR_STS register
	set BMCR_ANENABLE in vendor 2 MII_BMCR if
	  PHYLINK_PCS_NEG_INBAND_ENABLED

Which would avoid variability in register values when phylink
transitions the PCS between SGMII, 1000base-X and 2500base-X that
will occur today - e.g., when switching from either SGMII or
1000base-X to 2500base-X, then the following register fields do
not get written and are left how they were last configured:

	DW_VR_MII_AN_CTRL at all
	DW_VR_MII_PCS_MODE_MASK
	DW_VR_MII_TX_CONFIG_MASK
	DW_VR_MII_AN_CTRL_8BIT
	DW_VR_MII_DIG_CTRL1_PHY_MODE_CTRL

For example, switching from SGMII to 2500base-X, the
DW_VR_MII_PCS_MODE_MASK field will be left as
DW_VR_MII_PCS_MODE_C37_SGMII, but if switching from 1000base-X to
2500base-X, it will be DW_VR_MII_PCS_MODE_C37_1000BASEX.

Maybe it doesn't matter, because maybe setting
DW_VR_MII_DIG_CTRL1_2G5_EN overrides a whole host of register
configuration?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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