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    SubjectRe: [PATCH RFC 3/5] Add KSZ8795 switch driver
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    On 09/28/2017 11:40 AM, Pavel Machek wrote:
    > Hi!
    >
    > On Mon 2017-09-18 20:27:13, Tristram.Ha@microchip.com wrote:
    >>>> +/**
    >>>> + * Some counters do not need to be read too often because they are less
    >>> likely
    >>>> + * to increase much.
    >>>> + */
    >>>
    >>> What does comment mean? Are you caching statistics, and updating
    >>> different values at different rates?
    >>>
    >>
    >> There are 34 counters. In normal case using generic bus I/O or PCI to read them
    >> is very quick, but the switch is mostly accessed using SPI, or even I2C. As the SPI
    >> access is very slow and cannot run in interrupt context I keep worrying reading
    >> the MIB counters in a loop for 5 or more ports will prevent other critical hardware
    >> access from executing soon enough. These accesses can be getting 1588 PTP
    >> timestamps and opening/closing ports. (RSTP Conformance Test sends test traffic
    >> to port supposed to be closed/opened after receiving specific RSTP
    >> BPDU.)
    >
    > Hmm. Ok, interesting.
    >
    > I wonder how well this is going to work if userspace actively 'does
    > something' with the switch.
    >
    > It seems to me that even if your statistics code is careful not to do
    > 'a lot' of accesses at the same time, userspace can use other parts of
    > the driver to do the same, and thus cause same unwanted effects...

    A few switches have a MIB snapshot feature that is implemented such that
    accessing the snapshot does not hog the remainder of the switch
    registers, is this something possible on KSZ switches?

    Tangential: net-next is currently open, so now would be a good time to
    send a revised version of your patch series to target possibly 4.15 with
    an initial implementation. Please fix the cover-letter and patch
    threading such that they look like the following:

    [PATCH 0/X]
    [PATCH 1/X]
    [PATCH 2/X]
    etc..

    Right now this shows up as separate emails/patches and this is very
    annoying to follow as a thread.

    Thank you
    --
    Florian

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