linux-kernel - Re: [PATCH] net: mdiobus: Prevent spike on MDIO bus reset signal

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Message-ID: <YBIZyWZNoQeJ7Bt4@lunn.ch>
Date:   Thu, 28 Jan 2021 02:56:25 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Mike Looijmans <mike.looijmans@...ic.nl>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: mdiobus: Prevent spike on MDIO bus reset signal

On Tue, Jan 26, 2021 at 08:33:37AM +0100, Mike Looijmans wrote:
> The mdio_bus reset code first de-asserted the reset by allocating with
> GPIOD_OUT_LOW, then asserted and de-asserted again. In other words, if
> the reset signal defaulted to asserted, there'd be a short "spike"
> before the reset.
> 
> Instead, directly assert the reset signal using GPIOD_OUT_HIGH, this
> removes the spike and also removes a line of code since the signal
> is already high.

Hi Mike

Did you look at the per PHY reset? mdiobus_register_gpiod() gets the
GPIO with GPIOD_OUT_LOW. mdiobus_register_device() then immediately
sets it high.

So it looks like it suffers from the same problem.

   Andrew