netdev - Re: [PATCH 06/14] net: ks8851: Remove ks8851

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Message-ID: <20200324072219.wochifgdx2mz6orx@wunner.de>
Date:   Tue, 24 Mar 2020 08:22:19 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Marek Vasut <marex@...x.de>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Petr Stetiar <ynezz@...e.cz>,
        YueHaibing <yuehaibing@...wei.com>
Subject: Re: [PATCH 06/14] net: ks8851: Remove ks8851_rdreg32()

On Tue, Mar 24, 2020 at 12:42:55AM +0100, Marek Vasut wrote:
> The ks8851_rdreg32() is used only in one place, to read two registers
> using a single read. To make it easier to support 16-bit accesses via
> parallel bus later on, replace this single read with two 16-bit reads
> from each of the registers and drop the ks8851_rdreg32() altogether.

This doubles the SPI transactions necessary to read the RX queue status,
which happens for each received packet, so I expect the performance
impact to be noticeable.  Can you keep the 32-bit variant for SPI
and instead just introduce a 32-bit read for the MLL chip which performs
two 16-bit reads internally?

Thanks,

Lukas