linux-kernel - Re: [PATCH v2] net: mdiobus: Add a function to deassert reset

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Message-ID: <KL1PR01MB54486E8738DC81E062BA2D0EE6749@KL1PR01MB5448.apcprd01.prod.exchangelabs.com>
Date:   Thu, 11 May 2023 11:16:52 +0800
From:   Yan Wang <rk.code@...look.com>
To:     Alexander Stein <alexander.stein@...tq-group.com>, andrew@...n.ch
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "open list:ETHERNET PHY LIBRARY" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] net: mdiobus: Add a function to deassert reset



On 5/10/2023 7:55 PM, Alexander Stein wrote:
> Am Mittwoch, 10. Mai 2023, 10:02:52 CEST schrieb Yan Wang:
>> It is possible to mount multiple sub-devices on the mido bus.
> mdio bus
Yes, misspelled.
>> The hardware power-on does not necessarily reset these devices.
>> The device may be in an uncertain state, causing the device's ID
>> to be scanned.
>>
>> So, before adding a reset to the scan, make sure the device is in
>> normal working mode.
>>
>> I found that the subsequent drive registers the reset pin into the
>> structure of the sub-device to prevent conflicts, so release the
>> reset pin.
>>
>> Signed-off-by: Yan Wang <rk.code@...look.com>
> We had similar cases where the (single) PHY was in reset during Linux boot.
> Should you be able to make this work by using a "ethernet-phy-id%4x.%4x"
> compatible? See also [1]
>
> [1] https://lkml.org/lkml/2020/10/28/1139
Well, I've seen the [1] before, this method may mask some issues. For 
example ,if I use
another type of phy ,I have to modify the DT, Is it very cumbersome?
>> ---
>> v2:
>>    - fixed commit message
>>    - Using gpiod_ replace gpio_
>> v1:
>> https://lore.kernel.org/all/KL1PR01MB5448631F2D6F71021602117FE6769@KL1PR01M
>> B5448.apcprd01.prod.exchangelabs.com/ - Incorrect description of commit
>> message.
>>    - The gpio-api too old
>> ---
>>   drivers/net/mdio/fwnode_mdio.c | 16 ++++++++++++++++
>>   1 file changed, 16 insertions(+)
>>
>> diff --git a/drivers/net/mdio/fwnode_mdio.c b/drivers/net/mdio/fwnode_mdio.c
>> index 1183ef5e203e..6695848b8ef2 100644
>> --- a/drivers/net/mdio/fwnode_mdio.c
>> +++ b/drivers/net/mdio/fwnode_mdio.c
>> @@ -57,6 +57,20 @@ fwnode_find_mii_timestamper(struct fwnode_handle *fwnode)
>> return register_mii_timestamper(arg.np, arg.args[0]);
>>   }
>>
>> +static void fwnode_mdiobus_pre_enable_phy(struct fwnode_handle *fwnode)
>> +{
>> +	struct gpio_desc *reset;
>> +
>> +	reset = fwnode_gpiod_get_index(fwnode, "reset", 0, GPIOD_OUT_HIGH,
> NULL);
>> +	if (IS_ERR(reset) && PTR_ERR(reset) != -EPROBE_DEFER)
> How are you dealing with EPROBE_DEFER if the reset line is e.g. attached to an
> i2c expander, which is to be probed later on?
Thank you ,The logic is wrong,trying to fix it.
>> +		return;
>> +
>> +	usleep_range(100, 200);
> How do you know a PHY's reset pulse width?
>
>> +	gpiod_set_value_cansleep(reset, 0);
> What about post-reset stabilization times before MDIO access is allowed?
yes,I need to get reset pulse width and post-reset stabilization times 
from reset-assert-us and  reset-deassert-us. right?
>> +	/*Release the reset pin,it needs to be registered with the PHY.*/
> /* Release [...] PHY. */
>
> Best regards,
> Alexander
Thank you for your support.
>> +	gpiod_put(reset);
>> +}
>> +
>>   int fwnode_mdiobus_phy_device_register(struct mii_bus *mdio,
>>   				       struct phy_device *phy,
>>   				       struct fwnode_handle *child,
> u32 addr)
>> @@ -119,6 +133,8 @@ int fwnode_mdiobus_register_phy(struct mii_bus *bus,
>>   	u32 phy_id;
>>   	int rc;
>>
>> +	fwnode_mdiobus_pre_enable_phy(child);
>> +
>>   	psec = fwnode_find_pse_control(child);
>>   	if (IS_ERR(psec))
>>   		return PTR_ERR(psec);
>