linux-kernel - Re: [PATCH v2 net-next 2/2] net: dsa: realtek: rtl8365mb: serialize indirect PHY register access

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Date:   Tue, 22 Feb 2022 00:21:21 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Alvin Šipraga <alvin@...s.dk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Michael Rasmussen <MIR@...g-olufsen.dk>,
        Alvin Šipraga <ALSI@...g-olufsen.dk>,
        Luiz Angelo Daros de Luca <luizluca@...il.com>,
        Arınç ÜNAL <arinc.unal@...nc9.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next 2/2] net: dsa: realtek: rtl8365mb: serialize
 indirect PHY register access

On Mon, Feb 21, 2022 at 7:46 PM Alvin Šipraga <alvin@...s.dk> wrote:

> Realtek switches in the rtl8365mb family can access the PHY registers of
> the internal PHYs via the switch registers. This method is called
> indirect access. At a high level, the indirect PHY register access
> method involves reading and writing some special switch registers in a
> particular sequence. This works for both SMI and MDIO connected
> switches.

What I worry about is whether we need to do a similar patch to
rtl8366rb_phy_read() and rtl8366rb_phy_write() in
rtl8366rb.c?

And what about the upcoming rtl8367 driver?

> To fix this problem, one must guard against regmap access while the
> PHY indirect register read is executing. Fix this by using the newly
> introduced "nolock" regmap in all PHY-related functions, and by aquiring
> the regmap mutex at the top level of the PHY register access callbacks.
> Although no issue has been observed with PHY register _writes_, this
> change also serializes the indirect access method there. This is done
> purely as a matter of convenience and for reasons of symmetry.
>
> Fixes: 4af2950c50c8 ("net: dsa: realtek-smi: add rtl8365mb subdriver for RTL8365MB-VC")
> Link: https://lore.kernel.org/netdev/CAJq09z5FCgG-+jVT7uxh1a-0CiiFsoKoHYsAWJtiKwv7LXKofQ@mail.gmail.com/
> Link: https://lore.kernel.org/netdev/871qzwjmtv.fsf@bang-olufsen.dk/
> Reported-by: Arınç ÜNAL <arinc.unal@...nc9.com>
> Reported-by: Luiz Angelo Daros de Luca <luizluca@...il.com>
> Signed-off-by: Alvin Šipraga <alsi@...g-olufsen.dk>

This is a beautiful patch. Excellent job.
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij