netdev - Re: [PATCH RFC 3/5] Add KSZ8795 switch driver

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Date:   Fri, 29 Sep 2017 20:53:16 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Tristram.Ha@...rochip.com
Cc:     David.Laight@...LAB.COM, muvarov@...il.com, pavel@....cz,
        nathan.leigh.conrad@...il.com, vivien.didelot@...oirfairelinux.com,
        f.fainelli@...il.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Woojung.Huh@...rochip.com
Subject: Re: [PATCH RFC 3/5] Add KSZ8795 switch driver

> My concern is if a task is already running with SPI access to a lot
> of registers like reading the 32 MIB counters in every port of the
> switch, another register access has to wait until they are finished.

Why does it have to wait? Looking at the code in
ksz_get_ethtool_stats(), you don't take any mutex which will prevent
others from using the SPI bus. All there is is a mutex which prevents
two sets of ksz_get_ethtool_stats() at the same time.

So a PTP read could happen in parallel, and will not be blocked by MIB
reads. They should get interleaved access to the SPI bus.

       Andrew