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Date:   Mon, 17 Apr 2023 05:59:21 -0700
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Subject: Re: [PATCH net-next 3/7] net: mscc: ocelot: optimize ocelot_mm_irq()
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To:     Vladimir Oltean <vladimir.oltean@nxp.com>, netdev@vger.kernel.org
Cc:     Andrew Lunn <andrew@lunn.ch>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Claudiu Manoil <claudiu.manoil@nxp.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        UNGLinuxDriver@microchip.com,
        Xiaoliang Yang <xiaoliang.yang_1@nxp.com>,
        linux-kernel@vger.kernel.org
References: <20230415170551.3939607-1-vladimir.oltean@nxp.com>
 <20230415170551.3939607-4-vladimir.oltean@nxp.com>
From:   Florian Fainelli <f.fainelli@gmail.com>
In-Reply-To: <20230415170551.3939607-4-vladimir.oltean@nxp.com>
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On 4/15/2023 10:05 AM, Vladimir Oltean wrote:
> The MAC Merge IRQ of all ports is shared with the PTP TX timestamp IRQ
> of all ports, which means that currently, when a PTP TX timestamp is
> generated, felix_irq_handler() also polls for the MAC Merge layer status
> of all ports, looking for changes. This makes the kernel do more work,
> and under certain circumstances may make ptp4l require a
> tx_timestamp_timeout argument higher than before.
> 
> Changes to the MAC Merge layer status are only to be expected under
> certain conditions - its TX direction needs to be enabled - so we can
> check early if that is the case, and omit register access otherwise.
> 
> Make ocelot_mm_update_port_status() skip register access if
> mm->tx_enabled is unset, and also call it once more, outside IRQ
> context, from ocelot_port_set_mm(), when mm->tx_enabled transitions from
> true to false, because an IRQ is also expected in that case.
> 
> Also, a port may have its MAC Merge layer enabled but it may not have
> generated the interrupt. In that case, there's no point in writing to
> DEV_MM_STATUS to acknowledge that IRQ. We can reduce the number of
> register writes per port with MM enabled by keeping an "ack" variable
> which writes the "write-one-to-clear" bits. Those are 3 in number:
> PRMPT_ACTIVE_STICKY, UNEXP_RX_PFRM_STICKY and UNEXP_TX_PFRM_STICKY.
> The other fields in DEV_MM_STATUS are read-only and it doesn't matter
> what is written to them, so writing zero is just fine.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
-- 
Florian