Re: [PATCH net-next v5 02/19] net: stmmac: request the MDIO reset GPIO only once

[Linkui Xiao <xiaolinkui@126.com>]

On 2026/9/28 07:49, James Hilliard wrote:
> On Sun, Sep 27, 2026 at 5:35 PM Linus Walleij <linusw@kernel.org> wrote:
>>
>> Hi James,
>>
>> On Sun, Sep 27, 2026 at 11:59 PM James Hilliard
>> <james.hilliard1@gmail.com> wrote:
>>
>>> From: Linkui Xiao <xiaolinkui@kylinos.cn>
>>>
>>> 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.
>>>
>>> Parse the whole reset description, the GPIO and "snps,reset-delays-us",
>>> in stmmac_mdio_register() at probe time, and keep it 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,
>>> with the delays that were read once and for all at probe time.
>>>
>>> Cache the request and delays for DT devices regardless of
>>> mdio_bus_data->needs_reset. That flag controls the registration-time
>>> bus reset callback, but system resume calls stmmac_mdio_reset()
>>> directly. The reset routine no longer looks at the device tree: where
>>> the description is absent the cached descriptor is NULL and the delays
>>> are zero, so the pulse remains a no-op.
>>>
>>> Keep acquisition conditional on CONFIG_STMMAC_PLATFORM, matching the
>>> reset callback, so non-platform configurations do not request an unused
>>> GPIO. Also skip acquisition for a disabled MDIO child: registering that
>>> bus returns -ENODEV without calling its reset callback, and the driver
>>> must retain the existing disabled-bus success path even if the unused
>>> GPIO is unavailable. Remove the unnecessary gpio_desc forward declaration.
>>>
>>> Fixes: 7c86f20d15b7 ("net: stmmac: use GPIO descriptors in stmmac_mdio_reset")
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Linkui Xiao <xiaolinkui@kylinos.cn>
>>> Co-developed-by: James Hilliard <james.hilliard1@gmail.com>
>>> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
>>
>> Dostoyevsky commit message, I didn't read it. Ask the agent
>> to be terse.
> 
> That commit message style mostly just came from the imported patch,
> I'll change it to be more terse in the next revision:
> https://lore.kernel.org/all/20260921015727.2643540-1-xiaolinkui@126.com/Hi James,

Thanks for picking this up. Agreed the commit message is too long;
I'm fine with you trimming it for the next revision. Linus already
gave his Reviewed-by on the code, so the logic is settled.

Thanks,
Linkui

> 
>> I looked at the code and from a GPIO PoV it does the right
>> thing: use 1 as asserted and 0 as de-asserted RESET line.
>>
>> Reviewed-by: Linus Walleij <linusw@kernel.org>
>>
>> Yours,
>> Linus Walleij