linux-kernel - Re: [PATCH v2 2/2] PCI: uniphier: Add UniPhier PCIe endpoint controller support

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Message-ID: <20200319170659.GA158868@google.com>
Date:   Thu, 19 Mar 2020 12:06:59 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Andrew Murray <andrew.murray@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH v2 2/2] PCI: uniphier: Add UniPhier PCIe endpoint
 controller support

On Thu, Mar 19, 2020 at 04:54:09PM +0900, Kunihiko Hayashi wrote:
> This introduces specific glue layer for UniPhier platform to support
> PCIe controller that is based on the DesignWare PCIe core, and
> this driver supports endpoint mode. This supports for Pro5 SoC only.

Possible alternate text: ("specific glue layer" isn't the usual way to
describe a driver)

  PCI: uniphier: Add Socionext UniPhier Pro5 SoC endpoint controller driver

  Add driver for the Socionext UniPhier Pro5 SoC endpoint controller.
  This controller is based on the DesignWare PCIe core.

> +/* assertion time of intx in usec */

s/intx/INTx/ to match usage in spec (and in comments below :))

> +#define PCL_INTX_WIDTH_USEC		30

> +struct uniphier_pcie_ep_soc_data {
> +	bool is_legacy;

I'd prefer "unsigned int is_legacy:1".  See [1].

But AFAICT you actually don't need this at all (yet), since you only
have a single of_device_id, and it sets "is_legacy = true".  That
means the *not* legacy code is effectively dead and hasn't been
tested.

My preference would be to add "is_legacy" and the associated tests
when you actually *need* them, i.e., when you add support for a
non-legacy device.

> +static int uniphier_pcie_ep_raise_legacy_irq(struct dw_pcie_ep *ep)
> +{
> +	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
> +	struct uniphier_pcie_ep_priv *priv = to_uniphier_pcie(pci);
> +	u32 val;
> +
> +	/* assert INTx */
> +	val = readl(priv->base + PCL_APP_INTX);
> +	val |= PCL_APP_INTX_SYS_INT;
> +	writel(val, priv->base + PCL_APP_INTX);
> +
> +	udelay(PCL_INTX_WIDTH_USEC);
> +
> +	/* deassert INTx */
> +	val = readl(priv->base + PCL_APP_INTX);

Why do you need to read PCL_APP_INTX again here?

> +	val &= ~PCL_APP_INTX_SYS_INT;
> +	writel(val, priv->base + PCL_APP_INTX);
> +
> +	return 0;
> +}

> +	ret = dw_pcie_ep_init(ep);
> +	if (ret) {
> +		dev_err(dev, "Failed to initialize endpoint (%d)\n", ret);
> +		return ret;
> +	}
> +
> +	return 0;

This is equivalent to:

  ret = dw_pcie_ep_init(ep);
  if (ret)
    dev_err(dev, "Failed to initialize endpoint (%d)\n", ret);

  return ret;

> +}

[1] https://lore.kernel.org/linux-fsdevel/CA+55aFzKQ6Pj18TB8p4Yr0M4t+S+BsiHH=BJNmn=76-NcjTj-g@mail.gmail.com/