| Message ID | 20210202143239.10714-1-mike.looijmans@topic.nl |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] net: mdiobus: Prevent spike on MDIO bus reset signal | expand |
Hello: This patch was applied to netdev/net-next.git (refs/heads/master): On Tue, 2 Feb 2021 15:32:39 +0100 you wrote: > The mdio_bus reset code first de-asserted the reset by allocating with > GPIOD_OUT_LOW, then asserted and de-asserted again. In other words, if > the reset signal defaulted to asserted, there'd be a short "spike" > before the reset. > > Here is what happens depending on the pre-existing state of the reset > signal: > Reset (previously asserted): ~~~|_|~~~~|_______ > Reset (previously deasserted): _____|~~~~|_______ > ^ ^ ^ > A B C > > [...] Here is the summary with links: - [v2] net: mdiobus: Prevent spike on MDIO bus reset signal https://git.kernel.org/netdev/net-next/c/e0183b974d30 You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html
diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c index 2b42e46066b4..34e98ae75110 100644 --- a/drivers/net/phy/mdio_bus.c +++ b/drivers/net/phy/mdio_bus.c @@ -543,8 +543,8 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner) mutex_init(&bus->mdio_lock); mutex_init(&bus->shared_lock); - /* de-assert bus level PHY GPIO reset */ - gpiod = devm_gpiod_get_optional(&bus->dev, "reset", GPIOD_OUT_LOW); + /* assert bus level PHY GPIO reset */ + gpiod = devm_gpiod_get_optional(&bus->dev, "reset", GPIOD_OUT_HIGH); if (IS_ERR(gpiod)) { err = dev_err_probe(&bus->dev, PTR_ERR(gpiod), "mii_bus %s couldn't get reset GPIO\n", @@ -553,8 +553,6 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner) return err; } else if (gpiod) { bus->reset_gpiod = gpiod; - - gpiod_set_value_cansleep(gpiod, 1); fsleep(bus->reset_delay_us); gpiod_set_value_cansleep(gpiod, 0); if (bus->reset_post_delay_us > 0)
The mdio_bus reset code first de-asserted the reset by allocating with GPIOD_OUT_LOW, then asserted and de-asserted again. In other words, if the reset signal defaulted to asserted, there'd be a short "spike" before the reset. Here is what happens depending on the pre-existing state of the reset signal: Reset (previously asserted): ~~~|_|~~~~|_______ Reset (previously deasserted): _____|~~~~|_______ ^ ^ ^ A B C At point A, the low going transition is because the reset line is requested using GPIOD_OUT_LOW. If the line is successfully requested, the first thing we do is set it high _without_ any delay. This is point B. So, a glitch occurs between A and B. We then fsleep() and finally set the GPIO low at point C. Requesting the line using GPIOD_OUT_HIGH eliminates the A and B transitions. Instead we get: Reset (previously asserted) : ~~~~~~~~~~|______ Reset (previously deasserted): ____|~~~~~|______ ^ ^ A C Where A and C are the points described above in the code. Point B has been eliminated. The issue was found when we pulled down the reset signal for the Marvell 88E1512P PHY (because it requires at least 50ms after POR with an active clock). Looking at the reset signal with a scope revealed a short spike, point B in the artwork above. Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl> Reviewed-by: Andrew Lunn <andrew@lunn.ch> --- Changes in v2: Put more explanation into the commit text, and the artwork from Russell King drivers/net/phy/mdio_bus.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)