linux-kernel - Re: [PATCH v10 3/5] drivers/soc/litex: add LiteX SoC Controller driver

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Date:   Fri, 11 Sep 2020 09:57:40 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Mateusz Holenko <mholenko@...micro.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, devicetree@...r.kernel.org,
        linux-serial@...r.kernel.org, Karol Gugala <kgugala@...micro.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Filip Kokosinski <fkokosinski@...micro.com>,
        Pawel Czarnecki <pczarnecki@...ernships.antmicro.com>,
        Joel Stanley <joel@....id.au>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Maxime Ripard <mripard@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Sam Ravnborg <sam@...nborg.org>,
        Icenowy Zheng <icenowy@...c.io>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-kernel@...r.kernel.org, "Gabriel L. Somlo" <gsomlo@...il.com>
Subject: Re: [PATCH v10 3/5] drivers/soc/litex: add LiteX SoC Controller
 driver

On Wed, Aug 12, 2020 at 02:34:34PM +0200, Mateusz Holenko wrote:
> From: Pawel Czarnecki <pczarnecki@...ernships.antmicro.com>
> 
> This commit adds driver for the FPGA-based LiteX SoC
> Controller from LiteX SoC builder.
> 
> Co-developed-by: Mateusz Holenko <mholenko@...micro.com>
> Signed-off-by: Mateusz Holenko <mholenko@...micro.com>
> Signed-off-by: Pawel Czarnecki <pczarnecki@...ernships.antmicro.com>
> ---
...
> +static int litex_check_csr_access(void __iomem *reg_addr)
> +{
> +	unsigned long reg;
> +
> +	reg = litex_get_reg(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_SIZE);
> +
> +	if (reg != SCRATCH_REG_VALUE) {
> +		panic("Scratch register read error! Expected: 0x%x but got: 0x%lx",
> +			SCRATCH_REG_VALUE, reg);
> +		return -EINVAL;
> +	}
> +
> +	litex_set_reg(reg_addr + SCRATCH_REG_OFF,
> +		SCRATCH_REG_SIZE, SCRATCH_TEST_VALUE);
> +	reg = litex_get_reg(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_SIZE);
> +
> +	if (reg != SCRATCH_TEST_VALUE) {
> +		panic("Scratch register write error! Expected: 0x%x but got: 0x%lx",
> +			SCRATCH_TEST_VALUE, reg);
> +		return -EINVAL;
> +	}
> +
> +	/* restore original value of the SCRATCH register */
> +	litex_set_reg(reg_addr + SCRATCH_REG_OFF,
> +		SCRATCH_REG_SIZE, SCRATCH_REG_VALUE);
> +
> +	/* Set flag for other drivers */
What does this comment mean?

> +	pr_info("LiteX SoC Controller driver initialized");
> +
> +	return 0;
> +}
> +
> +struct litex_soc_ctrl_device {
> +	void __iomem *base;
> +};
> +
> +static const struct of_device_id litex_soc_ctrl_of_match[] = {
> +	{.compatible = "litex,soc-controller"},
> +	{},
> +};
> +
> +MODULE_DEVICE_TABLE(of, litex_soc_ctrl_of_match);
> +
> +static int litex_soc_ctrl_probe(struct platform_device *pdev)
> +{
> +	int result;
> +	struct device *dev;
> +	struct device_node *node;
> +	struct litex_soc_ctrl_device *soc_ctrl_dev;
> +
> +	dev = &pdev->dev;
> +	node = dev->of_node;
> +	if (!node)
> +		return -ENODEV;
> +
> +	soc_ctrl_dev = devm_kzalloc(dev, sizeof(*soc_ctrl_dev), GFP_KERNEL);
> +	if (!soc_ctrl_dev)
> +		return -ENOMEM;
> +
> +	soc_ctrl_dev->base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(soc_ctrl_dev->base))
> +		return PTR_ERR(soc_ctrl_dev->base);
> +
> +	result = litex_check_csr_access(soc_ctrl_dev->base);
> +	if (result) {
> +		// LiteX CSRs access is broken which means that
> +		// none of LiteX drivers will most probably
> +		// operate correctly
The comment format here with // is not usually used in the kernel, but its not
forbidded.  Could you use the /* */ multiline style?

> +		BUG();
Instead of stopping the system with BUG, could we just do:

	return litex_check_csr_access(soc_ctrl_dev->base);

We already have failure for NODEV/NOMEM so might as well not call BUG() here
too.

> +	}
> +
> +	return 0;
> +}
> +

Other than that it looks ok to me.

-Stafford