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Date:   Tue, 24 Oct 2023 16:08:31 +0200
From:   Andrew Lunn <andrew@lunn.ch>
To:     Romain Gantois <romain.gantois@bootlin.com>
Cc:     davem@davemloft.net, Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        thomas.petazzoni@bootlin.com,
        Florian Fainelli <f.fainelli@gmail.com>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org,
        Vladimir Oltean <vladimir.oltean@nxp.com>,
        Luka Perkov <luka.perkov@sartura.hr>,
        Robert Marko <robert.marko@sartura.hr>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@somainline.org>,
        Maxime Chevallier <maxime.chevallier@bootlin.com>
Subject: Re: [PATCH net-next 3/5] net: ipqess: introduce the Qualcomm IPQESS
 driver
Message-ID: <932bef01-b498-4c1a-a7f4-3357fe94e883@lunn.ch>
References: <20231023155013.512999-1-romain.gantois@bootlin.com>
 <20231023155013.512999-4-romain.gantois@bootlin.com>
 <b8ac3558-b6f0-4658-b406-8ceba062a52c@lunn.ch>
 <f4e6dcee-23cf-bf29-deef-cf876e63bb8a@bootlin.com>
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> > > +	for (c = 0; c < priv->info->mib_count; c++) {
> > > +		mib = &ar8327_mib[c];
> > > +		reg = QCA8K_PORT_MIB_COUNTER(port->index) + mib->offset;
> > > +
> > > +		ret = qca8k_read(priv, reg, &val);
> > > +		if (ret < 0)
> > > +			continue;
> > 
> > Given the switch is built in, is this fast? The 8k driver avoids doing
> > register reads for this.
> 
> Sorry, I don't quite understand what you mean. Are you referring to the existing 
> QCA8k DSA driver? From what I've seen, it calls qca8k_get_ethtool_stats defined 
> in qca8k-common.c and this uses the same register read.

It should actually build an Ethernet frame containing a command to get
most of the statistics in one operation. That frame is sent to the
switch over the SoCs ethernet interface. The switch replies with a
frame containing the statistics. This should be faster than doing lots
of register reads over a slow MDIO bus.

Now, given that this switch is built into the SoC, i assume the MDIO
bus is gone, so register access is fast. So you don't need to use
Ethernet frames.

	 Andrew