Re: [PATCH net v2] net: stmmac: request the MDIO reset GPIO only once

Hi Lorenzo,

On 2026/9/20 16:07, Lorenzo Bianconi wrote:

quoted

From: Linkui Xiao <redacted>

stmmac_mdio_reset() calls devm_gpiod_get_optional() every time it runs.
A GPIO line can only be requested once, so from the second call on
gpiod_request_commit() returns -EBUSY. devm_gpiod_get_optional() only
turns -ENOENT into NULL, hence the error is passed straight back and
stmmac_mdio_reset() bails out before pulsing "snps,reset" and before
running the STE101P MDC workaround.

The first call, made by of_mdiobus_register(), succeeds, so the failure
is only visible later on: every resume that does not use WoL goes
through stmmac_resume() -> stmmac_mdio_reset(), and that caller ignores
the return value, so the PHY silently stays un-reset.

The descriptor used to be requested exactly once: stmmac_mdio_reset()
resolved "snps,reset-gpio" itself and cached the GPIO number in
stmmac_mdio_bus_data::reset_gpio, and commit ae26c1c6cb9b ("stmmac: fix
PHY reset during resume") relies on that cache to reuse the line on
every call. commit 7c86f20d15b7 ("net: stmmac: use GPIO descriptors in
stmmac_mdio_reset") replaced it with a devm_gpiod_get_optional() that
caches nothing, so the request is repeated on every call and fails from
the second one on.

Request the GPIO in stmmac_mdio_register(), at probe time, and keep the
descriptor in struct stmmac_priv. This is where devm-gpiod is meant to be
used: the line is acquired with the device and released with it, and any
failure to acquire it is reported during probe instead of being ignored
by stmmac_resume(). stmmac_mdio_reset() then only pulses the cached line.

The request is still gated on mdio_bus_data->needs_reset, which is the
condition that installs the reset callback, and on the device using DT,
as the reset itself is.

Fixes: 7c86f20d15b7 ("net: stmmac: use GPIO descriptors in stmmac_mdio_reset")
Cc: stable@vger.kernel.org
Signed-off-by: Linkui Xiao <redacted>
---
Changes in v2:
- Do not request the GPIO from stmmac_mdio_reset(); request it once in
   stmmac_mdio_register() at probe time instead. (Maxime Chevallier)

  drivers/net/ethernet/stmicro/stmmac/stmmac.h  |  2 ++
  .../net/ethernet/stmicro/stmmac/stmmac_mdio.c | 19 ++++++++++---------
  2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index 7582fca63741..986fb43db45f 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -25,6 +25,7 @@
  #include <net/xdp.h>
  #include <uapi/linux/bpf.h>
  
+struct gpio_desc;
  struct stmmac_pcs;
  
  struct stmmac_resources {

@@ -287,6 +288,7 @@ struct stmmac_priv {
  
  	unsigned int pause_time;
  	struct mii_bus *mii;
+	struct gpio_desc *mdio_reset_gpio;
  
  	struct stmmac_pcs *integrated_pcs;
  

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
index afe98ff5bdcb..346f93f86abe 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c

@@ -386,15 +386,8 @@ int stmmac_mdio_reset(struct mii_bus *bus)
  
  #ifdef CONFIG_OF
  	if (priv->device->of_node) {
-		struct gpio_desc *reset_gpio;
  		u32 delays[3] = { 0, 0, 0 };
  
-		reset_gpio = devm_gpiod_get_optional(priv->device,
-						     "snps,reset",
-						     GPIOD_OUT_LOW);
-		if (IS_ERR(reset_gpio))
-			return PTR_ERR(reset_gpio);
-
  		device_property_read_u32_array(priv->device,
  					       "snps,reset-delays-us",
  					       delays, ARRAY_SIZE(delays));

nit: what about moving even these properties to stmmac_mdio_register()? It
seems a bit odd to have half of the parsing in stmmac_mdio_register() and
half in stmmac_mdio_reset(). What do you think?

Agreed, and thanks for pointing it out.

v3 reads "snps,reset-delays-us" in stmmac_mdio_register() as well and keeps
the three values in struct stmmac_priv, next to the descriptor, so the whole
reset description - the line and its timings - is parsed once, at probe 
time.
stmmac_mdio_reset() then only waits and pulses the cached line.

With the parsing gone, the callback doesn't need its CONFIG_OF/of_node guard
either, so I dropped that too: stmmac_mdio_reset() no longer looks at the
device tree at all. Where the description is absent, the cached descriptor
is NULL and the delays are all zero, so the pulse is a no-op - exactly what
the of_node check used to make of it. The request and the delays stay gated
on mdio_bus_data->needs_reset and on the device using DT, in
stmmac_mdio_register().

Nothing else changes: struct stmmac_priv is zeroed when it is allocated, so
a missing or short "snps,reset-delays-us" still gives the same all-zero
delays the local initialiser did.

Thanks,
Linkui

Regards,
Lorenzo

quoted

@@ -402,11 +395,11 @@ int stmmac_mdio_reset(struct mii_bus *bus)
  		if (delays[0])
  			msleep(DIV_ROUND_UP(delays[0], 1000));
  
-		gpiod_set_value_cansleep(reset_gpio, 1);
+		gpiod_set_value_cansleep(priv->mdio_reset_gpio, 1);
  		if (delays[1])
  			msleep(DIV_ROUND_UP(delays[1], 1000));
  
-		gpiod_set_value_cansleep(reset_gpio, 0);
+		gpiod_set_value_cansleep(priv->mdio_reset_gpio, 0);
  		if (delays[2])
  			msleep(DIV_ROUND_UP(delays[2], 1000));
  	}

@@ -608,6 +601,14 @@ int stmmac_mdio_register(struct net_device *ndev)
  	if (!mdio_bus_data)
  		return 0;
  
+	if (mdio_bus_data->needs_reset && dev_of_node(priv->device)) {
+		priv->mdio_reset_gpio =
+			devm_gpiod_get_optional(priv->device, "snps,reset",
+						GPIOD_OUT_LOW);
+		if (IS_ERR(priv->mdio_reset_gpio))
+			return PTR_ERR(priv->mdio_reset_gpio);
+	}
+
  	stmmac_mdio_bus_config(priv);
  
  	new_bus = mdiobus_alloc();

-- 
2.25.1