netdev - Re: igc: missing HW timestamps at TX

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Message-ID: <20220815222639.346wachaaq5zjwue@skbuf>
Date:   Mon, 15 Aug 2022 22:26:39 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
CC:     Ferenc Fejes <ferenc.fejes@...csson.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "marton12050@...il.com" <marton12050@...il.com>,
        "peti.antal99@...il.com" <peti.antal99@...il.com>
Subject: Re: igc: missing HW timestamps at TX

Hi Vinicius,

On Mon, Aug 15, 2022 at 02:39:33PM -0700, Vinicius Costa Gomes wrote:
> Just some aditional information (note that I know very little about
> interrupt internal workings), igc_intr_msi() is called when MSI-X is not
> enabled (i.e. "MSI only" system), igc_msix_other() is called when MSI-X
> is available. When MSI-X is available, i225/i226 sets up a separate
> interrupt handler for "general" events, the TX timestamp being available
> to be read from the registers is one those events.

Thanks for the extra information.

Why is the i225/i226 emitting an interrupt about the availability of a
new TX timestamp, if the igc driver polls for its availability anyway?
In other words, when IGC_TSICR_TXTS is found set, is a TX timestamp
available or is it not? Why does the driver schedule a deferred work
item to retrieve it?