Message-ID: <c03d114477b887048ea0348dbfd1adb53c139e9f.1607094989.git.wilken.gottwalt@posteo.net>
Date:   Fri, 4 Dec 2020 16:35:12 +0100
From:   Wilken Gottwalt <wilken.gottwalt@...teo.net>
To:     linux-kernel@...r.kernel.org
Cc:     Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        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: [PATCH v2 2/2] hwspinlock: add sunxi hardware spinlock support

Adds the sunxi_hwspinlock driver for the hardware spinlock unit found in
most of the sun8i and sun50i based SoCs.

This unit provides at least 32 spinlocks in hardware. The implementation
supports 32, 64, 128 or 256 32bit registers, where one lock can be taken
by reading a register and released by writing a 0 to it. This driver
supports all 4 spinlock setups, but for now only the first setup (32
locks) seem to exist in available devices. This spinlock unit is shared
between all ARM cores and the embedded OpenRisc AR100 core, all of them
can take/release a lock with a single cycle operation. It can be used to
sync access to devices shared by the ARM cores and the OpenRisc core.

There are two ways to check if a lock is taken. The first way is to read
a lock. If a 0 is returned, the lock was free and is taken now. If an 1
is returned, the caller has to try again, which means the lock is
currently taken. The second way is to read a 32bit wide status register
where every bit represents one of the 32 first locks. According to the
datasheets this status register supports the 32 first locks only. For
this reason the lock read/write approach is used in this driver which
can cover all 256 locks in the biggest setup.

Being able to use the status register to get knowledge about the locks
makes it suitable to extended testing. It also can be used to bypass
the Linux hwspinlock ABI completely and is not able to set locks. This
is used in one of the tests to show that the driver works correctly.

To run all tests it is necessary to take locks on the OpenRisc core and
show on the Linux side that the locks were taken by an external event.
This can be achived by using the crust firmware. For this the crust
firmware needs to be changed to take and release spinlocks (a simple
MMIO operation on the hwlock registers), which is currently not
supported by the current crust firmware. The necessary crust fork can
be found here https://github.com/wgottwalt/crust (hwspinlock branch).
It is also necessary to build u-boot with support for this crust/SCP
firmware. This u-boot fork can be found here
https://github.com/crust-firmware/u-boot (crust branch). For testing
this driver it is also necessary to pick a device that is fully
supported by crust. In this case a H5 based device works very well. In
this test a Friendlyarm NanoPi NEO2 was used, which is fully supported
by u-boot (also the fork) and current Linux kernels. In the crust fork
it is necessary to go into debug menu of "make nconfig" and select the
hwspinlock test loop, which uses the timeout functions of the crust
firmware. It loops through the first 32 spinlocks and takes/releases a
lock one after another using a timeout which can be set in the debug
menu.

Test 1:
This test was done with a mainline u-boot and a crust enabled u-boot.
For this a simple second kernel module was used, found here
https://github.com/wgottwalt/sunxi_hwspinlock/tree/main/test_module.

If run with mainline u-boot it shows that the Linux side correctly
takes a lock, tries to recursively take a lock again (which does not
happen) and releases a lock. Done for all 32 locks several times.

[  122.518435] [init]--- SUNXI HWSPINLOCK DRIVER TEST ---
[  122.523810] [run ]--- testing locks 0 to 31 ---
[  122.528370] [test] testing lock 0
[  122.531686] [test]+++ attempt #0 succeded
[  122.535709] [test]+++ attempt #1 succeded
[  122.539729] [test]+++ attempt #2 succeded
[  122.543752] [test] testing lock 1
[  122.547072] [test]+++ attempt #0 succeded
[  122.551093] [test]+++ attempt #1 succeded
[  122.555113] [test]+++ attempt #2 succeded
[  122.559129] [test] testing lock 2
...
[  123.004812] [test] testing lock 31
[  123.008208] [test]+++ attempt #0 succeded
[  123.012228] [test]+++ attempt #1 succeded
[  123.016250] [test]+++ attempt #2 succeded

Same test run with the hwspinlock test loop enabled in crust. Here the
test module hits two locks exactly in the moment crust switches from
lock 7 to 8. The test module code path is slower because of more code
that needs to be executed which makes this rare scenario possible.

[  122.620656] [test] testing lock 6
[  122.623966] [test]+++ attempt #0 succeded
[  122.627988] [test]+++ attempt #1 succeded
[  122.632008] [test]+++ attempt #2 succeded
[  122.636044] [test] testing lock 7
[  122.639364] [test] taking lock attempt #0 failed (-16)
[  122.644507] [run ]--- testing specific lock 7 failed (-14) ---
[  122.650345] [test] testing lock 8
[  122.653671] [test] taking lock attempt #0 failed (-16)
[  122.658818] [run ]--- testing specific lock 8 failed (-14) ---
[  122.664658] [test] testing lock 9
[  122.667971] [test]+++ attempt #0 succeded
[  122.671989] [test]+++ attempt #1 succeded

Test 2:
This is a more complex test that uses the status register to bypass the
Linux hwspinlock ABI. For this to work a slightly modified driver is
used and can be found here
https://github.com/wgottwalt/sunxi_hwspinlock/tree/main/
modified_sunxi_hwspinlock
This modified driver splits the 4K memory range into two and leaves the
status register untouched, so that it can be used by another test kernel
module which can be found here
https://github.com/wgottwalt/sunxi_hwspinlock/tree/main/test2_module
It is also necessary to change the device tree entries to get both
kernel modules working in parallel.

hwspinlock-mod@...8000 {
        compatible = "allwinner,sun50i-hwspinlock-mod";
        reg = <0x01c18000 0x4 0x01c18100 0x400>;
        clocks = <&ccu CLK_BUS_SPINLOCK>;
        clock-names = "ahb";
        resets = <&ccu RST_BUS_SPINLOCK>;
        reset-names = "ahb";
        status = "okay";
};

hwspinlock-stat@...8010 {
        compatible = "allwinner,sun50i-hwspinlock-stat";
        reg = <0x01c18010 0x4>;
        status = "okay";
};

The extended test kernel module supports 4 different modes of the test,
2 of them are sufficient to show the spinlock mechanism working.

Mode 1:
This one reads and prints the status register continuously. The crust
firmware and the test are set to a hwlock timeout of 1 second. The test
kernel module code runs a bit slower because of more code executed and
you can see how one lock is missed between entry 2 and 3.

> modprobe sunxi_hwspinlock_test2 mode=1 loops=10
[  187.167074] [init]--- SUNXI HWSPINLOCK DRIVER TEST ---
[  187.172636] [sreg] 00000000_00010000_00000000_00000000
[  188.196287] [sreg] 00000000_00001000_00000000_00000000
[  189.220285] [sreg] 00000000_00000010_00000000_00000000
[  190.244286] [sreg] 00000000_00000001_00000000_00000000
[  191.268285] [sreg] 00000000_00000000_10000000_00000000
[  192.292294] [sreg] 00000000_00000000_01000000_00000000
[  193.316302] [sreg] 00000000_00000000_00100000_00000000
[  194.340285] [sreg] 00000000_00000000_00010000_00000000
[  195.364285] [sreg] 00000000_00000000_00001000_00000000
[  196.388284] [sreg] 00000000_00000000_00000100_00000000

Mode 3:
This mode combines the Linux hwspinlock ABI approach from test 1 and the
status register access. The "after" reads show the locks taken by the
Linux driver and the crust firmware.

[  439.138476] [test] testing lock 13
[  439.141894] [sreg] before take 00000000_00000100_00000000_00000000
[  439.148083] [sreg] after take 00000000_00000110_00000000_00000000
[  439.154189] [sreg] after recursive take 00000000_00000110_00000000_00000000
[  439.161162] [sreg] after untake 00000000_00000010_00000000_00000000
[  439.167435] [test]+++ attempt #0 succeded
[  439.171458] [sreg] before take 00000000_00000010_00000000_00000000
[  439.177649] [sreg] after take 00000000_00000110_00000000_00000000
[  439.183751] [sreg] after recursive take 00000000_00000110_00000000_00000000
[  439.190725] [sreg] after untake 00000000_00000010_00000000_00000000
[  439.196992] [test]+++ attempt #1 succeded
[  439.201018] [sreg] before take 00000000_00000010_00000000_00000000
[  439.207212] [sreg] after take 00000000_00000110_00000000_00000000
[  439.213322] [sreg] after recursive take 00000000_00000110_00000000_00000000
[  439.220290] [sreg] after untake 00000000_00000010_00000000_00000000
[  439.226559] [test]+++ attempt #2 succeded
[  439.230576] [test] testing lock 14
[  439.233996] [sreg] before take 00000000_00000010_00000000_00000000
[  439.240177] [test] taking lock attempt #0 failed (-16)
[  439.245322] [run ]--- testing specific lock 14 failed (-14) ---
[  439.251252] [test] testing lock 15
[  439.254677] [sreg] before take 00000000_00000010_00000000_00000000
[  439.260865] [sreg] after take 00000000_00000011_00000000_00000000
[  439.266975] [sreg] after recursive take 00000000_00000011_00000000_00000000
[  439.273943] [sreg] after untake 00000000_00000010_00000000_00000000
[  439.280212] [test]+++ attempt #0 succeded
[  439.284235] [sreg] before take 00000000_00000010_00000000_00000000
[  439.290428] [sreg] after take 00000000_00000011_00000000_00000000
[  439.296534] [sreg] after recursive take 00000000_00000011_00000000_00000000
[  439.303502] [sreg] after untake 00000000_00000010_00000000_00000000
[  439.309774] [test]+++ attempt #1 succeded

Signed-off-by: Wilken Gottwalt <wilken.gottwalt@...teo.net>
---
Changes in v2:
  - added suggestions from Bjorn Andersson and Maxime Ripard
  - provided better driver and test description
---
 MAINTAINERS                           |   6 +
 drivers/hwspinlock/Kconfig            |   9 +
 drivers/hwspinlock/Makefile           |   1 +
 drivers/hwspinlock/sunxi_hwspinlock.c | 234 ++++++++++++++++++++++++++
 4 files changed, 250 insertions(+)
 create mode 100644 drivers/hwspinlock/sunxi_hwspinlock.c

diff --git a/MAINTAINERS b/MAINTAINERS
index ebe4829cdd4d..29a96a043cee 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..a568a4b5010c 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 most of the sun8i and sun50i 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..91adb2743aba
--- /dev/null
+++ b/drivers/hwspinlock/sunxi_hwspinlock.c
@@ -0,0 +1,234 @@
+// 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/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 per SoC */
+#define SPINLOCK_SYSSTATUS_REG	0x0000
+#define SPINLOCK_LOCK_REGN	0x0100
+#define SPINLOCK_NOTTAKEN	0
+
+struct sunxi_hwspinlock_data {
+	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 void sunxi_hwspinlock_debugfs_init(struct sunxi_hwspinlock_data *priv)
+{
+	priv->debugfs = debugfs_create_dir(DRIVER_NAME, NULL);
+	debugfs_create_file("supported", 0444, priv->debugfs, priv, &hwlocks_supported_fops);
+}
+
+#else
+
+static void sunxi_hwspinlock_debugfs_init(struct sunxi_hwspinlock_data *priv)
+{
+}
+
+#endif
+
+static int sunxi_hwspinlock_trylock(struct hwspinlock *lock)
+{
+	void __iomem *lock_addr = lock->priv;
+
+	return (readl(lock_addr) == SPINLOCK_NOTTAKEN);
+}
+
+static void sunxi_hwspinlock_unlock(struct hwspinlock *lock)
+{
+	void __iomem *lock_addr = lock->priv;
+
+	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 sunxi_hwspinlock_data *priv;
+	struct hwspinlock *hwlock;
+	void __iomem *io_base;
+	int num_banks, err, i;
+
+	io_base = devm_platform_ioremap_resource(pdev, SPINLOCK_BASE_ID);
+	if (IS_ERR(io_base)) {
+		err = PTR_ERR(io_base);
+		dev_err(&pdev->dev, "unable to request MMIO (%d)\n", err);
+		return err;
+	}
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	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)) {
+		return dev_err_probe(&pdev->dev, PTR_ERR(priv->reset),
+				     "unable to get reset control\n");
+	}
+
+	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, but at the same time the datasheet
+	 * says, bit 30 and 31 are reserved while the values can be 0 to 4, which is not reachable
+	 * by two bits alone, so the reserved bits are also taken into account
+	 *
+	 * order is important here, getting the amount of locks is only possible after setting up
+	 * clocks and resets
+	 */
+	num_banks = readl(io_base + SPINLOCK_SYSSTATUS_REG) >> 28;
+	switch (num_banks) {
+	case 1 ... 4:
+		/*
+		 * 32, 64, 128 and 256 spinlocks are supported by the hardware implementation,
+		 * though most of the SoCs support 32 spinlocks only
+		 */
+		priv->nlocks = 1 << (5 + i);
+		break;
+	default:
+		dev_err(&pdev->dev, "unsupported hwspinlock setup (%d)\n", num_banks);
+		return -EINVAL;
+	}
+
+	priv->bank = devm_kzalloc(&pdev->dev, struct_size(priv->bank, lock, priv->nlocks),
+				  GFP_KERNEL);
+	if (!priv->bank) {
+		err = -ENOMEM;
+		goto reset_fail;
+	}
+
+	for (i = 0; i < priv->nlocks; ++i) {
+		hwlock = &priv->bank->lock[i];
+		hwlock->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);
+	platform_set_drvdata(pdev, 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);
+
+	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	= sunxi_hwspinlock_ids,
+	},
+};
+
+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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