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

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Date:   Fri, 12 May 2023 10:01:41 +0200
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     andrew@...n.ch, Yan Wang <rk.code@...look.com>
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

Am Donnerstag, 11. Mai 2023, 05:16:52 CEST schrieb Yan Wang:
> 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?

You have to change the reset timings and possibly other properties as well if 
you change the PHY, so a DT change is necessary anyway.

Regards,
Alexander

> 
> >> ---
> >> 
> >> v2:
> >>    - fixed commit message
> >>    - Using gpiod_ replace gpio_
> >> 
> >> v1:
> >> https://lore.kernel.org/all/KL1PR01MB5448631F2D6F71021602117FE6769@KL1PR0
> >> 1M
> >> 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);


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