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Date:   Sat, 21 Nov 2020 23:19:00 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Wilken Gottwalt <wilken.gottwalt@...teo.net>
Cc:     linux-kernel@...r.kernel.org, Ohad Ben-Cohen <ohad@...ery.com>,
        Baolin Wang <baolin.wang7@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>
Subject: Re: [PATCH 2/2] hwspinlock: add sunxi hardware spinlock support

On Wed 18 Nov 04:02 CST 2020, Wilken Gottwalt wrote:

> Adds the sunxi_hwspinlock driver and updates makefiles/maintainers.
> 
> Signed-off-by: Wilken Gottwalt <wilken.gottwalt@...teo.net>
> ---
>  MAINTAINERS                           |   6 +
>  drivers/hwspinlock/Kconfig            |   9 +
>  drivers/hwspinlock/Makefile           |   1 +
>  drivers/hwspinlock/sunxi_hwspinlock.c | 282 ++++++++++++++++++++++++++
>  4 files changed, 298 insertions(+)
>  create mode 100644 drivers/hwspinlock/sunxi_hwspinlock.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 5cc595ac7b28..7765da172f10 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -722,6 +722,12 @@ L:	linux-crypto@...r.kernel.org
>  S:	Maintained
>  F:	drivers/crypto/allwinner/
>  
> +ALLWINNER HARDWARE SPINLOCK SUPPORT
> +M:	Wilken Gottwalt <wilken.gottwalt@...teo.net>
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/hwlock/sunxi-hwspinlock.yaml
> +F:	drivers/hwspinlock/sunxi_hwspinlock.c
> +
>  ALLWINNER THERMAL DRIVER
>  M:	Vasily Khoruzhick <anarsoul@...il.com>
>  M:	Yangtao Li <tiny.windzz@...il.com>
> diff --git a/drivers/hwspinlock/Kconfig b/drivers/hwspinlock/Kconfig
> index 32cd26352f38..27b6e22126f7 100644
> --- a/drivers/hwspinlock/Kconfig
> +++ b/drivers/hwspinlock/Kconfig
> @@ -55,6 +55,15 @@ config HWSPINLOCK_STM32
>  
>  	  If unsure, say N.
>  
> +config HWSPINLOCK_SUNXI
> +	tristate "SUNXI Hardware Spinlock device"
> +	depends on ARCH_SUNXI || COMPILE_TEST
> +	help
> +	  Say y here to support the Allwinner hardware mutex device available
> +	  in the H2+, H3, H5 and H6 SoCs.
> +
> +	  If unsure, say N.
> +
>  config HSEM_U8500
>  	tristate "STE Hardware Semaphore functionality"
>  	depends on ARCH_U8500 || COMPILE_TEST
> diff --git a/drivers/hwspinlock/Makefile b/drivers/hwspinlock/Makefile
> index ed053e3f02be..bf46bee95226 100644
> --- a/drivers/hwspinlock/Makefile
> +++ b/drivers/hwspinlock/Makefile
> @@ -9,4 +9,5 @@ obj-$(CONFIG_HWSPINLOCK_QCOM)		+= qcom_hwspinlock.o
>  obj-$(CONFIG_HWSPINLOCK_SIRF)		+= sirf_hwspinlock.o
>  obj-$(CONFIG_HWSPINLOCK_SPRD)		+= sprd_hwspinlock.o
>  obj-$(CONFIG_HWSPINLOCK_STM32)		+= stm32_hwspinlock.o
> +obj-$(CONFIG_HWSPINLOCK_SUNXI)		+= sunxi_hwspinlock.o
>  obj-$(CONFIG_HSEM_U8500)		+= u8500_hsem.o
> diff --git a/drivers/hwspinlock/sunxi_hwspinlock.c b/drivers/hwspinlock/sunxi_hwspinlock.c
> new file mode 100644
> index 000000000000..54e6ad3ac1c2
> --- /dev/null
> +++ b/drivers/hwspinlock/sunxi_hwspinlock.c
> @@ -0,0 +1,282 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * sunxi_hwspinlock.c - hardware spinlock driver for Allwinner SoCs
> + * Copyright (C) 2020 Wilken Gottwalt <wilken.gottwalt@...teo.net>
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/clk.h>
> +#include <linux/debugfs.h>
> +#include <linux/errno.h>
> +#include <linux/hwspinlock.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/reset.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.h>
> +
> +#include "hwspinlock_internal.h"
> +
> +#define DRIVER_NAME		"sunxi_hwspinlock"
> +
> +#define SPINLOCK_BASE_ID	0 /* there is only one hwspinlock device in each SoC */
> +#define SPINLOCK_SYSSTATUS_REG	0x0000
> +#define SPINLOCK_STATUS_REG	0x0010
> +#define SPINLOCK_LOCK_REGN	0x0100
> +#define SPINLOCK_NOTTAKEN	0
> +#define SPINLOCK_TAKEN		1
> +
> +struct sunxi_hwspinlock {
> +	void __iomem *io_base;
> +};
> +
> +struct sunxi_hwspinlock_data {
> +	void __iomem *io_base;
> +	struct hwspinlock_device *bank;
> +	struct reset_control *reset;
> +	struct clk *ahb_clock;
> +	struct dentry *debugfs;
> +	int nlocks;
> +};
> +
> +#ifdef CONFIG_DEBUG_FS
> +
> +static int hwlocks_supported_show(struct seq_file *seqf, void *unused)
> +{
> +	struct sunxi_hwspinlock_data *priv = seqf->private;
> +
> +	seq_printf(seqf, "%d\n", priv->nlocks);
> +
> +	return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(hwlocks_supported);
> +
> +static int hwlocks_inuse_show(struct seq_file *seqf, void *unused)
> +{
> +	struct sunxi_hwspinlock_data *priv = seqf->private;
> +	int inuse;
> +
> +	/* getting the status of only the main 32 spinlocks is supported */
> +	inuse = hweight32(readl(priv->io_base + SPINLOCK_STATUS_REG));

So this returns how many of the locks are taken? How is that useful?

> +	seq_printf(seqf, "%d\n", inuse);
> +
> +	return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(hwlocks_inuse);
> +
> +static void sunxi_hwspinlock_debugfs_init(struct sunxi_hwspinlock_data *priv)
> +{
> +	char name[32];
> +
> +	scnprintf(name, sizeof(name), "%s", DRIVER_NAME);

Why not just pass DRIVER_NAME directly to debugfs_create_dir()?

> +
> +	priv->debugfs = debugfs_create_dir(name, NULL);
> +	debugfs_create_file("hwlocks_supported", 0444, priv->debugfs, priv,
> +			    &hwlocks_supported_fops);
> +	debugfs_create_file("hwlocks_inuse", 0444, priv->debugfs, priv, &hwlocks_inuse_fops);
> +}
> +
> +#else
> +
> +static void sunxi_hwspinlock_debugfs_init(struct sunxi_hwspinlock_data *priv)
> +{
> +}
> +
> +#endif
> +
> +static int sunxi_hwspinlock_trylock(struct hwspinlock *lock)
> +{
> +	struct sunxi_hwspinlock_data *priv = lock->priv;
> +	void __iomem *lock_addr = priv->io_base;
> +
> +	return (readl(lock_addr) == SPINLOCK_NOTTAKEN);
> +}
> +
> +static void sunxi_hwspinlock_unlock(struct hwspinlock *lock)
> +{
> +	struct sunxi_hwspinlock_data *priv = lock->priv;
> +	void __iomem *lock_addr = priv->io_base;
> +
> +	writel(SPINLOCK_NOTTAKEN, lock_addr);
> +}
> +
> +static const struct hwspinlock_ops sunxi_hwspinlock_ops = {
> +	.trylock	= sunxi_hwspinlock_trylock,
> +	.unlock		= sunxi_hwspinlock_unlock,
> +};
> +
> +static int sunxi_hwspinlock_probe(struct platform_device *pdev)
> +{
> +	struct device_node *node = pdev->dev.of_node;

I don't see a need for this, or the check to fail if it's NULL. Please
remove it.

> +	struct sunxi_hwspinlock_data *priv;
> +	struct sunxi_hwspinlock *hwpriv;
> +	struct hwspinlock *hwlock;
> +	struct resource *res;
> +	int num_banks, err, i;
> +
> +	if (!node)
> +		return -ENODEV;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!res)
> +		return -ENODEV;
> +
> +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->io_base = devm_ioremap_resource(&pdev->dev, res);

Please use devm_platform_ioremap_resource() instead.

> +	if (IS_ERR(priv->io_base)) {
> +		err = PTR_ERR(priv->io_base);
> +		dev_err(&pdev->dev, "unable to request MMIO (%d)\n", err);
> +		return err;
> +	}
> +
> +	priv->ahb_clock = devm_clk_get(&pdev->dev, "ahb");
> +	if (IS_ERR(priv->ahb_clock)) {
> +		err = PTR_ERR(priv->ahb_clock);
> +		dev_err(&pdev->dev, "unable to get AHB clock (%d)\n", err);
> +		return err;
> +	}
> +
> +	priv->reset = devm_reset_control_get_optional(&pdev->dev, "ahb");
> +	if (IS_ERR(priv->reset)) { > +		err = PTR_ERR(priv->reset);
> +		if (err == -EPROBE_DEFER)
> +			return err;
> +
> +		dev_info(&pdev->dev, "no optional reset control available (%d)\n", err);

In the even that no "ahb" reset is specified priv->reset is NULL, as
such if you get here there's something wrong - so it's better to fail
here.

And you can use the convenient dev_err_probe() function to deal with the
EPROBE_DEFER.

> +		priv->reset = NULL;
> +	}
> +
> +	if (priv->reset) {

It's perfectly fine to call reset_control_deassert(NULL); so you can
omit this check.

> +		err = reset_control_deassert(priv->reset);
> +		if (err) {
> +			dev_err(&pdev->dev, "deassert reset control failure (%d)\n", err);
> +			return err;
> +		}
> +	}
> +
> +	err = clk_prepare_enable(priv->ahb_clock);
> +	if (err) {
> +		dev_err(&pdev->dev, "unable to prepare AHB clock (%d)\n", err);
> +		goto reset_fail;
> +	}
> +
> +	/* bit 28 and 29 hold the amount of spinlock banks */
> +	num_banks = (readl(priv->io_base + SPINLOCK_SYSSTATUS_REG) >> 28) & 0x03;
> +	switch (num_banks) {
> +	case 1 ... 4:

But the comment above says...and num_banks was & 0x3, so how can it be ...4?

> +		/*
> +		 * 32, 64, 128 and 256 spinlocks are supported by the hardware implementation,
> +		 * though most only support 32 spinlocks
> +		 */
> +		priv->nlocks = 1 << (4 + num_banks);
> +		break;
> +	default:

Given the mask above I believe this would only happen if bits 28 and 29
are both 0...

Regardless I think that this would be better written as a

if (num_banks == invalid) {
	...
	goto fail;
}

priv->nlocks = ...;

> +		dev_err(&pdev->dev, "unsupported hwspinlock setup (%d)\n", num_banks);
> +		err = -EINVAL;
> +		goto fail;
> +	}
> +
> +	/*
> +	 * the Allwinner hwspinlock device uses 32bit registers for representing every single
> +	 * spinlock, which is a real waste of space
> +	 */

Might be a waste, but having them be the natural write size in hardware
makes sense. I'm however not sure what this comment has to do with the
following allocation.

> +	priv->bank = devm_kzalloc(&pdev->dev, priv->nlocks * sizeof(*hwlock) + sizeof(*priv->bank),

Consider using struct_size() here.

> +				  GFP_KERNEL);
> +	if (!priv->bank) {
> +		err = -ENOMEM;
> +		goto fail;

If you do this allocation before you start the clock and deassert the
reset you can just return -ENOMEM here, instead of the goto.

> +	}
> +
> +	for (i = 0, hwlock = &priv->bank->lock[0]; i < priv->nlocks; ++i, ++hwlock) {
> +		hwlock->priv = devm_kzalloc(&pdev->dev, sizeof(struct sunxi_hwspinlock),
> +					    GFP_KERNEL);

		hwpriv = devm_kzalloc(&pdev->dev, sizeof(*hwpriv), GFP_KERNEL);
		if (!hwpriv)
			return -ENOMEM;

		hwpriv->io_base = ...;
		priv->bank->lock[i].priv = hwpriv;


> +		if (!hwlock->priv) {
> +			err = -ENOMEM;
> +			goto fail;
> +		}
> +
> +		hwpriv = hwlock->priv;
> +		hwpriv->io_base = priv->io_base + SPINLOCK_LOCK_REGN + sizeof(u32) * i;
> +	}
> +
> +	err = hwspin_lock_register(priv->bank, &pdev->dev, &sunxi_hwspinlock_ops, SPINLOCK_BASE_ID,
> +				   priv->nlocks);
> +	if (err) {
> +		dev_err(&pdev->dev, "unable to register hwspinlocks (%d)\n", err);
> +		goto fail;
> +	}
> +
> +	sunxi_hwspinlock_debugfs_init(priv);
> +
> +	dev_dbg(&pdev->dev, "SUNXI hardware spinlock driver enabled (%d locks)\n", priv->nlocks);
> +
> +	return 0;
> +
> +fail:
> +	clk_disable_unprepare(priv->ahb_clock);
> +
> +reset_fail:
> +	if (priv->reset)
> +		reset_control_assert(priv->reset);
> +
> +	return err;
> +}
> +
> +static int sunxi_hwspinlock_remove(struct platform_device *pdev)
> +{
> +	struct sunxi_hwspinlock_data *priv = platform_get_drvdata(pdev);
> +	int err;
> +
> +	debugfs_remove_recursive(priv->debugfs);
> +
> +	err = hwspin_lock_unregister(priv->bank);
> +	if (err) {
> +		dev_err(&pdev->dev, "unregister device failed (%d)\n", err);
> +		return err;
> +	}
> +
> +	if (priv->reset)
> +		reset_control_assert(priv->reset);
> +
> +	clk_disable_unprepare(priv->ahb_clock);

By using devm_add_action_or_reset() to set up an "assert and unprepare"-
function you can use devm_hwspin_lock_register(), you can drop the
remove function and you can clean up your sunxi_hwspinlock_data (e.g.
you no longer need a pointer to priv->bank).

> +
> +	return 0;
> +}
> +
> +static const struct of_device_id sunxi_hwspinlock_ids[] = {
> +	{ .compatible = "allwinner,sun8i-hwspinlock", },
> +	{ .compatible = "allwinner,sun50i-hwspinlock", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, sunxi_hwspinlock_ids);
> +
> +static struct platform_driver sunxi_hwspinlock_driver = {
> +	.probe	= sunxi_hwspinlock_probe,
> +	.remove	= sunxi_hwspinlock_remove,
> +	.driver	= {
> +		.name		= DRIVER_NAME,
> +		.of_match_table	= of_match_ptr(sunxi_hwspinlock_ids),

Please avoid of_match_ptr, as this will cause warnings about unused
variables when COMPILE_TEST without OF.

Regards,
Bjorn

> +	},
> +};
> +
> +static int __init sunxi_hwspinlock_init(void)
> +{
> +	return platform_driver_register(&sunxi_hwspinlock_driver);
> +}
> +postcore_initcall(sunxi_hwspinlock_init);
> +
> +static void __exit sunxi_hwspinlock_exit(void)
> +{
> +	platform_driver_unregister(&sunxi_hwspinlock_driver);
> +}
> +module_exit(sunxi_hwspinlock_exit);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("SUNXI hardware spinlock driver");
> +MODULE_AUTHOR("Wilken Gottwalt <wilken.gottwalt@...teo.net>");
> -- 
> 2.29.2
> 

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