linux-kernel - Re: [PATCH net-next] net: phy: perform a PHY reset on resume

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Date:   Mon, 13 Dec 2021 10:57:42 +0000
From:   Philippe Schenker <philippe.schenker@...adex.com>
To:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "qiangqing.zhang@....com" <qiangqing.zhang@....com>
CC:     "festevam@...il.com" <festevam@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: perform a PHY reset on resume

On Sat, 2021-12-11 at 14:01 +0100, Francesco Dolcini wrote:
> Perform a PHY reset in phy_init_hw() to ensure that the PHY is working
> after resume. This is required if the PHY was powered down in suspend
> like it is done by the freescale FEC driver in fec_suspend().
> 
> Link:
> https://lore.kernel.org/netdev/20211206101326.1022527-1-philippe.schenker@toradex.com/
> Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
> 
> ---
> 
> Philippe: what about something like that? Only compile tested, but I
> see no reason for this not solving the issue.
> 
> Any delay required on the reset can be specified using reset-assert-
> us/reset-deassert-us.

That would of course be the easiest way. However I understand Russel's
concerns here, as every PHY is again different and this is basically a
hardware-specific design.

I like Joakin's idea to add a phy_reset_after_power_on() function in
phylib similar to phy_reset_after_clk_enable(). I will prepare a
patchset for that so we can discuss further there.

Philippe
> 
> ---
>  drivers/net/phy/phy_device.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/phy_device.c
> b/drivers/net/phy/phy_device.c
> index 74d8e1dc125f..7eab0c054adf 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -1158,7 +1158,8 @@ int phy_init_hw(struct phy_device *phydev)
>  {
>         int ret = 0;
>  
> -       /* Deassert the reset signal */
> +       /* phy reset required if the phy was powered down during
> suspend */
> +       phy_device_reset(phydev, 1);
>         phy_device_reset(phydev, 0);
>  
>         if (!phydev->drv)