netdev - Re: [PATCH v2 2/2] net: Add driver for LiteX's LiteEth network interface

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Date:   Wed, 25 Aug 2021 06:35:17 +0000
From:   Joel Stanley <joel@....id.au>
To:     "Gabriel L. Somlo" <gsomlo@...il.com>,
        Florent Kermarrec <florent@...oy-digital.fr>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Karol Gugala <kgugala@...micro.com>,
        Mateusz Holenko <mholenko@...micro.com>,
        devicetree <devicetree@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Shah <dave@....me>, Stafford Horne <shorne@...il.com>
Subject: Re: [PATCH v2 2/2] net: Add driver for LiteX's LiteEth network interface

On Tue, 24 Aug 2021 at 19:43, Gabriel L. Somlo <gsomlo@...il.com> wrote:
>
> Hi Joel,
>
> Couple of comments below:
>
> On Fri, Aug 20, 2021 at 05:17:26PM +0930, Joel Stanley wrote:

> > diff --git a/drivers/net/ethernet/litex/Kconfig b/drivers/net/ethernet/litex/Kconfig
> > new file mode 100644
> > index 000000000000..265dba414b41
> > --- /dev/null
> > +++ b/drivers/net/ethernet/litex/Kconfig

> > +
> > +config LITEX_LITEETH
> > +     tristate "LiteX Ethernet support"
>
> Mostly cosmetic, but should there be a "depends on LITEX" statement in here?

No, there's as there is no dependency on the litex soc driver.

> Maybe also "select MII" and "select PHYLIB"?

Again, there is no mii or phy code so the driver doesn't need these.

> > diff --git a/drivers/net/ethernet/litex/Makefile b/drivers/net/ethernet/litex/Makefile
> > new file mode 100644
> > index 000000000000..9343b73b8e49
> > --- /dev/null
> > +++ b/drivers/net/ethernet/litex/Makefile
> > +int liteeth_setup_slots(struct liteeth *priv)
> > +{
> > +     struct device_node *np = priv->dev->of_node;
> > +     int err, depth;
> > +
> > +     err = of_property_read_u32(np, "rx-fifo-depth", &depth);
> > +     if (err) {
> > +             dev_err(priv->dev, "unable to get rx-fifo-depth\n");
> > +             return err;
> > +     }
> > +     if (depth < LITEETH_BUFFER_SIZE) {
>
> If I set depth to be *equal* to LITEETH_BUFFER_SIZE (2048) in DTS,
> no traffic makes it out of my network interface (linux-on-litex-rocket
> on an ecpix5 board, see github.com/litex-hub/linux-on-litex-rocket).
>
> May I suggest rejecting if (depth / LITEETH_BUFFER_SIZE < 2) instead?
> When that's enforced, the interface actually works fine for me.

Yes, I was using BUFFER_SIZE as the slot size, which it is not. I'll
rework it to use the slot size I think.

I spent some time digging through the migen source and I couldn't work
out where the 1024 length comes from. If anything it should be
eth_mtu, which is 1530.

Florent, can you clear that up?

>
> > +             dev_err(priv->dev, "invalid tx-fifo-depth: %d\n", depth);
>
> This should read "rx-fifo-depth".

Thanks.

>
> > +             return -EINVAL;
> > +     }
> > +     priv->num_rx_slots = depth / LITEETH_BUFFER_SIZE;
> > +
> > +     err = of_property_read_u32(np, "tx-fifo-depth", &depth);
> > +     if (err) {
> > +             dev_err(priv->dev, "unable to get tx-fifo-depth\n");
> > +             return err;
> > +     }
> > +     if (depth < LITEETH_BUFFER_SIZE) {
>
> Ditto reject if (depth / LITEETH_BUFFER_SIZE < 2) instead.
>
> > +             dev_err(priv->dev, "invalid rx-fifo-depth: %d\n", depth);
>
> This should read "tx-fifo-depth".

Ack.

>
> > +             return -EINVAL;
> > +     }
> > +     priv->num_tx_slots = depth / LITEETH_BUFFER_SIZE;
> > +
> > +     return 0;
> > +}
> > +
> > +static int liteeth_probe(struct platform_device *pdev)
> > +{
> > +     struct net_device *netdev;
> > +     void __iomem *buf_base;
> > +     struct resource *res;
> > +     struct liteeth *priv;
> > +     int irq, err;
> > +
> > +     netdev = devm_alloc_etherdev(&pdev->dev, sizeof(*priv));
> > +     if (!netdev)
> > +             return -ENOMEM;
> > +
> > +     SET_NETDEV_DEV(netdev, &pdev->dev);
> > +     platform_set_drvdata(pdev, netdev);
> > +
> > +     priv = netdev_priv(netdev);
> > +     priv->netdev = netdev;
> > +     priv->dev = &pdev->dev;
> > +
> > +     irq = platform_get_irq(pdev, 0);
> > +     if (irq < 0) {
> > +             dev_err(&pdev->dev, "Failed to get IRQ %d\n", irq);
> > +             return irq;
>
> At this point, netdev has been dynamically allocated, and should
> probably be free'd before liteeth_probe() is allowed to fail,
> to avoid any potential leaks...

We use the managed variant of alloc_etherdev, which means the
structure is freed by the driver core when the driver is removed. This
saves having to open code the cleanup/free code.

Have a read of Documentation/driver-api/driver-model/devres.rst for
more information.

Thanks for the review Gabriel. I'll send a v3 with some fixes for the
fifo buffer handling.

Cheers,

Joel