netdev - [PATCH net 0/4] Restore and fix PHY reset for SMSC LAN8720

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Date:   Tue, 27 Oct 2020 23:25:01 +0000
From:   "Badel, Laurent" <LaurentBadel@...on.com>
To:     "davem@...emloft.net" <davem@...emloft.net>,
        "m.felsch@...gutronix.de" <m.felsch@...gutronix.de>,
        "fugang.duan@....com" <fugang.duan@....com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "richard.leitner@...data.com" <richard.leitner@...data.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>
CC:     "Quette, Arnaud" <ArnaudQuette@...on.com>
Subject: [PATCH net 0/4] Restore and fix PHY reset for SMSC LAN8720

Subject: [PATCH net 0/4] Restore and fix PHY reset for SMSC LAN8720

Description:
A recent patchset [1] added support in the SMSC PHY driver for managing
the ref clock and therefore removed the PHY_RST_AFTER_CLK_EN flag for the
LAN8720 chip. The ref clock is passed to the SMSC driver through a new
property "clocks" in the device tree.

There appears to be two potential caveats:
(i) Building kernel 5.9 without updating the DT with the "clocks"
property for SMSC PHY, would break systems previously relying on the PHY
reset workaround (SMSC driver cannot grab the ref clock, so it is still
managed by FEC, but the PHY is not reset because PHY_RST_AFTER_CLK_EN is
not set). This may lead to occasional loss of ethernet connectivity in
these systems, that is difficult to debug.

(ii) This defeats the purpose of a previous commit [2] that disabled the
ref clock for power saving reasons. If a ref clock for the PHY is
specified in DT, the SMSC driver will keep it always on (confirmed with 
scope). While this removes the need for additional PHY resets (only a 
single reset is needed after power up), this prevents the FEC from saving
power by disabling the refclk. Since there may be use cases where one is
interested in saving power, keep this option available when no ref clock
is specified for the PHY, by fixing issues with the PHY reset.

Main changes proposed to address this:
(a) Restore PHY_RST_AFTER_CLK_EN for LAN8720, but explicitly clear it if
the SMSC driver succeeds in retrieving the ref clock.
(b) Fix phy_reset_after_clk_enable() to work in interrupt mode, by
re-configuring the PHY registers after reset.

Tests: against net tree 5.9, including allyes/no/modconfig. 10 pieces of
an iMX28-EVK-based board were tested, 3 of which were found to exhibit
issues when the "clocks" property was left unset. Issues were fixed by
the present patchset.

References:
[1] commit d65af21842f8 ("net: phy: smsc: LAN8710/20: remove
    PHY_RST_AFTER_CLK_EN flag")
    commit bedd8d78aba3 ("net: phy: smsc: LAN8710/20: add phy refclk in
    support")
[2] commit e8fcfcd5684a ("net: fec: optimize the clock management to save
    power")

Laurent Badel (5):
  net:phy:smsc: enable PHY_RST_AFTER_CLK_EN if ref clock is not set
  net:phy:smsc: expand documentation of clocks property
  net:phy: add phy_device_reset_status() support
  net:phy: fix phy_reset_after_clk_enable()
  net:phy: add SMSC PHY reset on PM restore

 .../devicetree/bindings/net/smsc-lan87xx.txt  |  3 +-
 drivers/net/phy/mdio_device.c                 | 18 +++++++++++
 drivers/net/phy/phy_device.c                  | 32 +++++++++++++++----
 drivers/net/phy/smsc.c                        |  5 ++-
 include/linux/mdio.h                          |  1 +
 include/linux/phy.h                           |  5 +++
 6 files changed, 55 insertions(+), 9 deletions(-)

-- 
2.17.1

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