netdev - Re: [PATCH net-next v3 1/6] net: phy: mscc: migrate to phy_select/restore

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Message-ID: <mvm4lcdaynt.fsf@suse.de>
Date:   Mon, 19 Nov 2018 16:13:10 +0100
From:   Andreas Schwab <schwab@...e.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Quentin Schulz <quentin.schulz@...tlin.com>, davem@...emloft.net,
        f.fainelli@...il.com, allan.nielsen@...rochip.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        thomas.petazzoni@...tlin.com, alexandre.belloni@...tlin.com,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH net-next v3 1/6] net: phy: mscc: migrate to phy_select/restore_page functions

On Nov 19 2018, Andrew Lunn <andrew@...n.ch> wrote:

> On Mon, Nov 19, 2018 at 03:57:17PM +0100, Andreas Schwab wrote:
>> On Okt 08 2018, Quentin Schulz <quentin.schulz@...tlin.com> wrote:
>> 
>> > The Microsemi PHYs have multiple banks of registers (called pages).
>> > Registers can only be accessed from one page, if we need a register from
>> > another page, we need to switch the page and the registers of all other
>> > pages are not accessible anymore.
>> >
>> > Basically, to read register 5 from page 0, 1, 2, etc., you do the same
>> > phy_read(phydev, 5); but you need to set the desired page beforehand.
>> >
>> > In order to guarantee that two concurrent functions do not change the
>> > page, we need to do some locking per page. This can be achieved with the
>> > use of phy_select_page and phy_restore_page functions but phy_write/read
>> > calls in-between those two functions shall be replaced by their
>> > lock-free alternative __phy_write/read.
>> >
>> > Let's migrate this driver to those functions.
>> 
>> This has some serious locking problem.
>
> Hi Andreas
>
> Could you be more specific. Are you getting a deadlock? A WARN_ON?

See the stack trace.  That's where it hangs.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@...e.de
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