linux-kernel - Re: [PATCH net-next v16 3/3] net: ax88796c: ASIX AX88796C SPI Ethernet Adapter Driver

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Date:   Wed, 13 Oct 2021 23:14:20 +0200
From:   Lukasz Stelmach <l.stelmach@...sung.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>, jim.cromie@...il.com,
        Heiner Kallweit <hkallweit1@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org,
        Bartłomiej Żolnierkiewicz 
        <b.zolnierkie@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH net-next v16 3/3] net: ax88796c: ASIX AX88796C SPI
 Ethernet Adapter Driver

It was <2021-10-01 pią 15:39>, when Jakub Kicinski wrote:
> On Wed, 29 Sep 2021 16:08:54 +0200 Łukasz Stelmach wrote:
>> +static char *no_regs_list = "80018001,e1918001,8001a001,fc0d0000";
>
> static const char ...
>
>> +static int
>> +ax88796c_close(struct net_device *ndev)
>> +{
>> +	struct ax88796c_device *ax_local = to_ax88796c_device(ndev);
>> +
>> +	netif_stop_queue(ndev);
>
> This can run concurrently with the work which restarts the queue.
> You should take the mutex and purge the queue here, so that there 
> is no chance queue will get restarted by the work right after.
>> +	phy_stop(ndev->phydev);
>> +
>> +	mutex_lock(&ax_local->spi_lock);

This was a bit tricky. The function now looks like this (details in the
comments). In theory there is a chance of dropping a packet if the
ax88796c_work() runs between phy_stop() and mutex_lock(), but I'd say
the overall risk is negligible.

--8<---------------cut here---------------start------------->8---
static int
ax88796c_close(struct net_device *ndev)
{
        struct ax88796c_device *ax_local = to_ax88796c_device(ndev);

        phy_stop(ndev->phydev);

        /* We lock the mutex early not only to protect the device
         * against concurrent access, but also avoid waking up the
         * queue in ax88796c_work(). phy_stop() needs to be called
         * before because it locks the mutex to access SPI.
         */
        mutex_lock(&ax_local->spi_lock);

        netif_stop_queue(ndev);

        /* No more work can be scheduled now. Make any pending work,
         * including one already waiting for the mutex to be unlocked,
         * NOP.
         */
        clear_bit(EVENT_SET_MULTI, &ax_local->flags);
        clear_bit(EVENT_INTR, &ax_local->flags);
        clear_bit(EVENT_TX, &ax_local->flags);

        /* Disable MAC interrupts */
        AX_WRITE(&ax_local->ax_spi, IMR_MASKALL, P0_IMR);
        __skb_queue_purge(&ax_local->tx_wait_q);
        ax88796c_soft_reset(ax_local);

        mutex_unlock(&ax_local->spi_lock);

        cancel_work_sync(&ax_local->ax_work);

        free_irq(ndev->irq, ndev);

        return 0;
}
--8<---------------cut here---------------end--------------->8---



>> +MODULE_AUTHOR("ASIX");
>
> You can drop this, author should be human.

I looked at diff --stat and decided it is OK to put my name there (-;
-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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