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CC:     <yangyicong@hisilicon.com>, <coresight@lists.linaro.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>, <lpieralisi@kernel.org>,
        <linuxarm@huawei.com>, <liuqi115@huawei.com>,
        <f.fangjian@huawei.com>, <prime.zeng@hisilicon.com>
Subject: Re: [PATCH v12 1/2] drivers/coresight: Add UltraSoc System Memory
 Buffer driver
To:     Junhao He <hejunhao3@huawei.com>, <mathieu.poirier@linaro.org>,
        <suzuki.poulose@arm.com>, <mike.leach@linaro.org>,
        <leo.yan@linaro.org>, <jonathan.cameron@huawei.com>,
        <john.garry@huawei.com>
References: <20221109135008.9485-1-hejunhao3@huawei.com>
 <20221109135008.9485-2-hejunhao3@huawei.com>
From:   Yicong Yang <yangyicong@huawei.com>
Message-ID: <c394c88a-8c81-fd03-f031-1ca3e2ca85ed@huawei.com>
Date:   Thu, 10 Nov 2022 20:05:59 +0800
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Hi Junhao,

On 2022/11/9 21:50, Junhao He wrote:
> From: Qi Liu <liuqi115@huawei.com>
> 
> This patch adds driver for UltraSoc SMB(System Memory Buffer)
> device. SMB provides a way to buffer messages from ETM, and
> store these "CPU instructions trace" in system memory.
> 
> SMB is developed by UltraSoc technology, which is acquired by
> Siemens, and we still use "UltraSoc" to name driver.
> 

Some comments inline.

> Signed-off-by: Qi Liu <liuqi115@huawei.com>
> Signed-off-by: Junhao He <hejunhao3@huawei.com>
> Tested-by: JunHao He <hejunhao3@huawei.com>
> ---
>  drivers/hwtracing/coresight/Kconfig        |  11 +
>  drivers/hwtracing/coresight/Makefile       |   1 +
>  drivers/hwtracing/coresight/ultrasoc-smb.c | 635 +++++++++++++++++++++
>  drivers/hwtracing/coresight/ultrasoc-smb.h | 116 ++++
>  4 files changed, 763 insertions(+)
>  create mode 100644 drivers/hwtracing/coresight/ultrasoc-smb.c
>  create mode 100644 drivers/hwtracing/coresight/ultrasoc-smb.h
> 
> diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
> index 45c1eb5dfcb7..cb17c207a728 100644
> --- a/drivers/hwtracing/coresight/Kconfig
> +++ b/drivers/hwtracing/coresight/Kconfig
> @@ -201,4 +201,15 @@ config CORESIGHT_TRBE
>  
>  	  To compile this driver as a module, choose M here: the module will be
>  	  called coresight-trbe.
> +
> +config ULTRASOC_SMB
> +	tristate "Ultrasoc system memory buffer drivers"
> +	depends on ARM64 && CORESIGHT_LINKS_AND_SINKS
> +	help
> +	  This driver provides support for the Ultrasoc system memory buffer (SMB).
> +	  SMB is responsible for receiving the trace data from Coresight ETM devices
> +	  and storing them to a system buffer.
> +
> +	  To compile this driver as a module, choose M here: the module will be
> +	  called ultrasoc-smb.
>  endif
> diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile
> index b6c4a48140ec..344dba8d6ff8 100644
> --- a/drivers/hwtracing/coresight/Makefile
> +++ b/drivers/hwtracing/coresight/Makefile
> @@ -27,3 +27,4 @@ obj-$(CONFIG_CORESIGHT_CTI) += coresight-cti.o
>  obj-$(CONFIG_CORESIGHT_TRBE) += coresight-trbe.o
>  coresight-cti-y := coresight-cti-core.o	coresight-cti-platform.o \
>  		   coresight-cti-sysfs.o
> +obj-$(CONFIG_ULTRASOC_SMB) += ultrasoc-smb.o
> diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.c b/drivers/hwtracing/coresight/ultrasoc-smb.c
> new file mode 100644
> index 000000000000..ea2552a98d28
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/ultrasoc-smb.c
> @@ -0,0 +1,635 @@
> +// SPDX-License-Identifier: (GPL-2.0 OR MIT)
> +/*
> + * Siemens System Memory Buffer driver.
> + * Copyright(c) 2022, HiSilicon Limited.
> + */
> +
> +#include <linux/atomic.h>
> +#include <linux/acpi.h>
> +#include <linux/circ_buf.h>
> +#include <linux/err.h>
> +#include <linux/fs.h>
> +#include <linux/module.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/platform_device.h>
> +
> +#include "coresight-etm-perf.h"
> +#include "coresight-priv.h"
> +#include "ultrasoc-smb.h"
> +
> +DEFINE_CORESIGHT_DEVLIST(sink_devs, "ultra_smb");
> +
> +#define ULTRASOC_SMB_DSM_UUID	"82ae1283-7f6a-4cbe-aa06-53e8fb24db18"
> +
> +static bool smb_buffer_is_empty(struct smb_drv_data *drvdata)
> +{
> +	u32 buf_status = readl(drvdata->base + SMB_LB_INT_STS_REG);
> +
> +	return !FIELD_PREP(SMB_LB_INT_STS_NOT_EMPTY_MSK, buf_status);

Should be FIELD_GET() here?

> +}
> +
> +static void smb_buffer_sync_status(struct smb_drv_data *drvdata)
> +{
> +	struct smb_data_buffer *sdb = &drvdata->sdb;
> +
> +	sdb->wr_offset = readl(drvdata->base + SMB_LB_WR_ADDR_REG) - sdb->start_addr;
> +	sdb->rd_offset = readl(drvdata->base + SMB_LB_RD_ADDR_REG) - sdb->start_addr;
> +	sdb->full = sdb->wr_offset == sdb->rd_offset && !smb_buffer_is_empty(drvdata);

Mistake here? Why to overwrite wr_offset?

> +}
> +
> +static void smb_reset_buffer_status(struct smb_drv_data *drvdata)
> +{
> +	writel(SMB_LB_INT_BUF_STS_RESET, drvdata->base + SMB_LB_INT_STS_REG);

You'll reset other fields of SMB_LB_INT_STS_REG since SMB_LB_INT_BUF_STS_RESET is only
BIT [3, 0], if it's not intended I'd suggest to only update the necessary fields. So is
other places.

> +}
> +
> +/* Purge data remaining in hardware path in case them influence next trace */
> +static void smb_purge_data(struct smb_drv_data *drvdata)
> +{
> +	writel(SMB_LB_PURGE_PURGED, drvdata->base + SMB_LB_PURGE_REG);
> +}
> +
> +static void smb_update_data_size(struct smb_drv_data *drvdata)
> +{
> +	struct smb_data_buffer *sdb = &drvdata->sdb;
> +
> +	smb_purge_data(drvdata);
> +	smb_buffer_sync_status(drvdata);
> +	if (sdb->full) {
> +		sdb->data_size = sdb->buf_size;
> +		return;
> +	}
> +
> +	sdb->data_size = CIRC_CNT(sdb->wr_offset, sdb->rd_offset, sdb->buf_size);
> +}
> +
> +static int smb_open(struct inode *inode, struct file *file)
> +{
> +	struct smb_drv_data *drvdata = container_of(file->private_data,
> +					struct smb_drv_data, miscdev);
> +	int ret = 0;
> +
> +	mutex_lock(&drvdata->mutex);
> +
> +	if (local_read(&drvdata->reading)) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	if (atomic_read(drvdata->csdev->refcnt)) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	local_set(&drvdata->reading, 1);
> +out:
> +	mutex_unlock(&drvdata->mutex);
> +
> +	return ret;
> +}
> +
> +static ssize_t smb_read(struct file *file, char __user *data, size_t len,
> +			loff_t *ppos)
> +{
> +	struct smb_drv_data *drvdata = container_of(file->private_data,
> +					struct smb_drv_data, miscdev);
> +	struct smb_data_buffer *sdb = &drvdata->sdb;
> +	struct device *dev = &drvdata->csdev->dev;
> +	ssize_t to_copy = 0;
> +
> +	mutex_lock(&drvdata->mutex);
> +
> +	if (!sdb->data_size) {
> +		smb_update_data_size(drvdata);
> +		if (!sdb->data_size)
> +			goto out;
> +	}
> +

It'd be better to check this earlier in open().

> +	to_copy = min(sdb->data_size, len);
> +
> +	/* Copy parts of trace data when read pointer wrap around SMB buffer */
> +	if (sdb->rd_offset + to_copy > sdb->buf_size)
> +		to_copy = sdb->buf_size - sdb->rd_offset;
> +
> +	if (copy_to_user(data, (void *)sdb->buf_base + sdb->rd_offset,
> +			 to_copy)) {
> +		dev_dbg(dev, "Failed to copy data to user\n");
> +		to_copy = -EFAULT;
> +		goto out;
> +	}
> +
> +	*ppos += to_copy;
> +	sdb->data_size -= to_copy;
> +	sdb->rd_offset += to_copy;
> +	sdb->rd_offset %= sdb->buf_size;
> +	writel(sdb->start_addr + sdb->rd_offset,
> +	       drvdata->base + SMB_LB_RD_ADDR_REG);
> +	dev_dbg(dev, "%zu bytes copied\n", to_copy);
> +out:
> +	if (!sdb->data_size)
> +		smb_reset_buffer_status(drvdata);
> +	mutex_unlock(&drvdata->mutex);
> +
> +	return to_copy;
> +}
> +
> +static int smb_release(struct inode *inode, struct file *file)
> +{
> +	struct smb_drv_data *drvdata = container_of(file->private_data,
> +					struct smb_drv_data, miscdev);
> +
> +	mutex_lock(&drvdata->mutex);
> +	local_set(&drvdata->reading, 0);
> +	mutex_unlock(&drvdata->mutex);
> +
> +	return 0;
> +}
> +
> +static const struct file_operations smb_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= smb_open,
> +	.read		= smb_read,
> +	.release	= smb_release,
> +	.llseek		= no_llseek,
> +};
> +
> +static ssize_t buf_size_show(struct device *dev, struct device_attribute *attr,
> +			     char *buf)
> +{
> +	struct smb_drv_data *drvdata = dev_get_drvdata(dev->parent);
> +
> +	return sysfs_emit(buf, "0x%lx\n", drvdata->sdb.buf_size);

Need to update the data size before sysfs_emit().

> +}
> +static DEVICE_ATTR_RO(buf_size);
> +
> +static struct attribute *smb_sink_attrs[] = {
> +	coresight_simple_reg32(read_pos, SMB_LB_RD_ADDR_REG),
> +	coresight_simple_reg32(write_pos, SMB_LB_WR_ADDR_REG),
> +	coresight_simple_reg32(buf_status, SMB_LB_INT_STS_REG),
> +	&dev_attr_buf_size.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group smb_sink_group = {
> +	.attrs = smb_sink_attrs,
> +	.name = "mgmt",
> +};
> +
> +static const struct attribute_group *smb_sink_groups[] = {
> +	&smb_sink_group,
> +	NULL
> +};
> +
> +static void smb_enable_hw(struct smb_drv_data *drvdata)
> +{
> +	writel(SMB_GLB_EN_HW_ENABLE, drvdata->base + SMB_GLB_EN_REG);
> +}
> +
> +static void smb_disable_hw(struct smb_drv_data *drvdata)
> +{
> +	writel(0x0, drvdata->base + SMB_GLB_EN_REG);
> +}
> +
> +static void smb_enable_sysfs(struct coresight_device *csdev)
> +{
> +	struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
> +
> +	if (drvdata->mode != CS_MODE_DISABLED)
> +		return;
> +
> +	smb_enable_hw(drvdata);
> +	drvdata->mode = CS_MODE_SYSFS;
> +}
> +
> +static int smb_enable_perf(struct coresight_device *csdev, void *data)
> +{
> +	struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
> +	struct perf_output_handle *handle = data;
> +	struct cs_buffers *buf = etm_perf_sink_config(handle);
> +	pid_t pid;
> +
> +	if (!buf)
> +		return -EINVAL;
> +
> +	/* Get a handle on the pid of the target process */
> +	pid = buf->pid;
> +
> +	/* Device is already in used by other session */
> +	if (drvdata->pid != -1 && drvdata->pid != pid)
> +		return -EBUSY;
> +
> +	if (drvdata->pid == -1) {
> +		smb_enable_hw(drvdata);
> +		drvdata->pid = pid;
> +		drvdata->mode = CS_MODE_PERF;
> +	}
> +
> +	return 0;
> +}
> +
> +static int smb_enable(struct coresight_device *csdev, u32 mode, void *data)
> +{
> +	struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
> +	int ret = 0;
> +
> +	mutex_lock(&drvdata->mutex);
> +
> +	/* Do nothing, the trace data is reading by other interface now */
> +	if (local_read(&drvdata->reading)) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	/* Do nothing, the SMB is already enabled as other mode */
> +	if (drvdata->mode != CS_MODE_DISABLED && drvdata->mode != mode) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	switch (mode) {
> +	case CS_MODE_SYSFS:
> +		smb_enable_sysfs(csdev);
> +		break;
> +	case CS_MODE_PERF:
> +		ret = smb_enable_perf(csdev, data);
> +		break;
> +	default:
> +		ret = -EINVAL;
> +	}
> +
> +	if (ret)
> +		goto out;
> +
> +	atomic_inc(csdev->refcnt);
> +
> +	dev_dbg(&csdev->dev, "Ultrasoc SMB enabled\n");
> +out:
> +	mutex_unlock(&drvdata->mutex);
> +
> +	return ret;
> +}
> +
> +static int smb_disable(struct coresight_device *csdev)
> +{
> +	struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
> +	int ret = 0;
> +
> +	mutex_lock(&drvdata->mutex);
> +
> +	if (local_read(&drvdata->reading)) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	if (atomic_dec_return(csdev->refcnt)) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	/* Complain if we (somehow) got out of sync */
> +	WARN_ON_ONCE(drvdata->mode == CS_MODE_DISABLED);

Is there any conditions we can reach here? I see we always update
drvdata->mode within the mutex's protection.

> +
> +	smb_disable_hw(drvdata);
> +	smb_purge_data(drvdata);
> +
> +	/* Dissociate from the target process. */
> +	drvdata->pid = -1;
> +	drvdata->mode = CS_MODE_DISABLED;
> +
> +	dev_dbg(&csdev->dev, "Ultrasoc SMB disabled\n");
> +out:
> +	mutex_unlock(&drvdata->mutex);
> +
> +	return ret;
> +}
> +
> +static void *smb_alloc_buffer(struct coresight_device *csdev,
> +			      struct perf_event *event, void **pages,
> +			      int nr_pages, bool overwrite)
> +{
> +	struct cs_buffers *buf;
> +	int node;
> +
> +	node = (event->cpu == -1) ? NUMA_NO_NODE : cpu_to_node(event->cpu);
> +	buf = kzalloc_node(sizeof(struct cs_buffers), GFP_KERNEL, node);
> +	if (!buf)
> +		return NULL;
> +
> +	buf->snapshot = overwrite;
> +	buf->nr_pages = nr_pages;
> +	buf->data_pages = pages;
> +	buf->pid = task_pid_nr(event->owner);
> +
> +	return buf;
> +}
> +
> +static void smb_free_buffer(void *config)
> +{
> +	struct cs_buffers *buf = config;
> +
> +	kfree(buf);
> +}
> +
> +static void smb_sync_perf_buffer(struct smb_drv_data *drvdata,
> +				 struct cs_buffers *buf,
> +				 unsigned long head,
> +				 unsigned long data_size)
> +{
> +	struct smb_data_buffer *sdb = &drvdata->sdb;
> +	char **dst_pages = (char **)buf->data_pages;
> +	unsigned long to_copy;
> +	long pg_idx, pg_offset;
> +
> +	pg_idx = head >> PAGE_SHIFT;
> +	pg_offset = head & (PAGE_SIZE - 1);
> +
> +	while (data_size) {
> +		unsigned long pg_space = PAGE_SIZE - pg_offset;
> +
> +		/* Copy parts of trace data when read pointer wrap around */
> +		if (sdb->rd_offset + pg_space > sdb->buf_size)
> +			to_copy = sdb->buf_size - sdb->rd_offset;
> +		else
> +			to_copy = min(data_size, pg_space);
> +
> +		memcpy(dst_pages[pg_idx] + pg_offset,
> +			      sdb->buf_base + sdb->rd_offset, to_copy);
> +
> +		pg_offset += to_copy;
> +		if (pg_offset >= PAGE_SIZE) {
> +			pg_offset = 0;
> +			pg_idx++;
> +			pg_idx %= buf->nr_pages;
> +		}
> +		data_size -= to_copy;
> +		sdb->rd_offset += to_copy;
> +		sdb->rd_offset %= sdb->buf_size;
> +	}
> +
> +	sdb->data_size = 0;
> +	writel(sdb->start_addr + sdb->rd_offset, drvdata->base + SMB_LB_RD_ADDR_REG);
> +
> +	/*
> +	 * Data remained in link cannot be purged when SMB is full, so
> +	 * synchronize the read pointer to write pointer, to make sure
> +	 * these remained data won't influence next trace.
> +	 */
> +	if (sdb->full) {
> +		smb_purge_data(drvdata);
> +		writel(readl(drvdata->base + SMB_LB_WR_ADDR_REG),
> +		       drvdata->base + SMB_LB_RD_ADDR_REG);
> +	}
> +	smb_reset_buffer_status(drvdata);
> +}
> +
> +static unsigned long smb_update_buffer(struct coresight_device *csdev,
> +				       struct perf_output_handle *handle,
> +				       void *sink_config)
> +{
> +	struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
> +	struct smb_data_buffer *sdb = &drvdata->sdb;
> +	struct cs_buffers *buf = sink_config;
> +	unsigned long data_size = 0;
> +	bool lost = false;
> +
> +	if (!buf)
> +		return 0;
> +
> +	mutex_lock(&drvdata->mutex);
> +
> +	/* Don't do anything if another tracer is using this sink. */
> +	if (atomic_read(csdev->refcnt) != 1)
> +		goto out;
> +
> +	smb_disable_hw(drvdata);
> +	smb_update_data_size(drvdata);
> +	data_size = sdb->data_size;
> +
> +	/*
> +	 * The SMB buffer may be bigger than the space available in the
> +	 * perf ring buffer (handle->size). If so advance the offset so
> +	 * that we get the latest trace data.
> +	 */
> +	if (data_size > handle->size) {
> +		sdb->rd_offset += data_size - handle->size;
> +		sdb->rd_offset %= sdb->buf_size;
> +		data_size = handle->size;
> +		lost = true;
> +	}
> +
> +	smb_sync_perf_buffer(drvdata, buf, handle->head, data_size);
> +	if (!buf->snapshot && lost)
> +		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
> +
> +	smb_enable_hw(drvdata);
> +out:
> +	mutex_unlock(&drvdata->mutex);
> +
> +	return data_size;
> +}
> +
> +static const struct coresight_ops_sink smb_cs_ops = {
> +	.enable		= smb_enable,
> +	.disable	= smb_disable,
> +	.alloc_buffer	= smb_alloc_buffer,
> +	.free_buffer	= smb_free_buffer,
> +	.update_buffer	= smb_update_buffer,
> +};
> +
> +static const struct coresight_ops cs_ops = {
> +	.sink_ops	= &smb_cs_ops,
> +};
> +
> +static int smb_init_data_buffer(struct platform_device *pdev,
> +				struct smb_data_buffer *sdb)
> +{
> +	struct resource *res;
> +	void __iomem *base;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, SMB_BUF_ADDR_RES);
> +	if (IS_ERR(res)) {
> +		dev_err(&pdev->dev, "SMB device failed to get resource\n");
> +		return -EINVAL;
> +	}
> +
> +	sdb->start_addr = FIELD_PREP(SMB_BUF_ADDR_LO_MSK, res->start);

also FIELD_GET()?

> +	sdb->buf_size = resource_size(res);
> +	if (sdb->buf_size == 0)
> +		return -EINVAL;
> +
> +	/*
> +	 * This is a chunk of memory, use classic mapping with better
> +	 * performance.
> +	 */
> +	base = devm_memremap(&pdev->dev, sdb->start_addr, sdb->buf_size,
> +				MEMREMAP_WB);
> +	if (IS_ERR(base))
> +		return PTR_ERR(base);
> +
> +	sdb->buf_base = base;
> +
> +	return 0;
> +}
> +
> +static void smb_init_hw(struct smb_drv_data *drvdata)
> +{
> +	/* First disable SMB and clear the status of SMB buffer */
> +	smb_reset_buffer_status(drvdata);
> +	smb_disable_hw(drvdata);
> +	smb_purge_data(drvdata);
> +
> +	writel(SMB_LB_CFG_LO_DEFAULT, drvdata->base + SMB_LB_CFG_LO_REG);
> +	writel(SMB_LB_CFG_HI_DEFAULT, drvdata->base + SMB_LB_CFG_HI_REG);
> +	writel(SMB_GLB_CFG_DEFAULT, drvdata->base + SMB_GLB_CFG_REG);
> +	writel(SMB_GLB_INT_CFG, drvdata->base + SMB_GLB_INT_REG);
> +	writel(SMB_LB_INT_CTRL_CFG, drvdata->base + SMB_LB_INT_CTRL_REG);
> +}
> +
> +static int smb_register_sink(struct platform_device *pdev,
> +			     struct smb_drv_data *drvdata)
> +{
> +	struct coresight_platform_data *pdata = NULL;
> +	struct coresight_desc desc = { 0 };
> +	int ret;
> +
> +	pdata = coresight_get_platform_data(&pdev->dev);
> +	if (IS_ERR(pdata))
> +		return PTR_ERR(pdata);
> +
> +	desc.type = CORESIGHT_DEV_TYPE_SINK;
> +	desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_BUFFER;
> +	desc.ops = &cs_ops;
> +	desc.pdata = pdata;
> +	desc.dev = &pdev->dev;
> +	desc.groups = smb_sink_groups;
> +	desc.name = coresight_alloc_device_name(&sink_devs, &pdev->dev);
> +	if (!desc.name) {
> +		dev_err(&pdev->dev, "Failed to alloc coresight device name");
> +		return -ENOMEM;
> +	}
> +	desc.access = CSDEV_ACCESS_IOMEM(drvdata->base);
> +
> +	drvdata->csdev = coresight_register(&desc);
> +	if (IS_ERR(drvdata->csdev))
> +		return PTR_ERR(drvdata->csdev);
> +
> +	drvdata->miscdev.name = desc.name;
> +	drvdata->miscdev.minor = MISC_DYNAMIC_MINOR;
> +	drvdata->miscdev.fops = &smb_fops;
> +	ret = misc_register(&drvdata->miscdev);
> +	if (ret) {
> +		coresight_unregister(drvdata->csdev);
> +		dev_err(&pdev->dev, "Failed to register misc, ret=%d\n", ret);
> +	}
> +
> +	return ret;
> +}
> +
> +static void smb_unregister_sink(struct smb_drv_data *drvdata)
> +{
> +	misc_deregister(&drvdata->miscdev);
> +	coresight_unregister(drvdata->csdev);
> +}
> +
> +static int smb_config_inport(struct device *dev, bool enable)
> +{
> +	u64 func = enable ? 1 : 0;
> +	union acpi_object *obj;
> +	guid_t guid;
> +	u64 rev = 0;
> +
> +	/*
> +	 * Using DSM calls to enable/disable ultrasoc hardwares on
> +	 * tracing path, to prevent ultrasoc packet format being exposed.
> +	 */
> +	if (guid_parse(ULTRASOC_SMB_DSM_UUID, &guid)) {
> +		dev_err(dev, "Get GUID failed\n");
> +		return -EINVAL;
> +	}
> +
> +	obj = acpi_evaluate_dsm(ACPI_HANDLE(dev), &guid, rev, func, NULL);
> +	if (!obj)
> +		dev_err(dev, "ACPI handle failed\n");
> +	else
> +		ACPI_FREE(obj);
> +
> +	return 0;
> +}
> +
> +static int smb_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct smb_drv_data *drvdata;
> +	int ret;
> +
> +	drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
> +	if (!drvdata)
> +		return -ENOMEM;
> +
> +	drvdata->base = devm_platform_ioremap_resource(pdev, SMB_REG_ADDR_RES);
> +	if (IS_ERR(drvdata->base)) {
> +		dev_err(dev, "Failed to ioremap resource\n");
> +		return PTR_ERR(drvdata->base);
> +	}
> +
> +	ret = smb_init_data_buffer(pdev, &drvdata->sdb);
> +	if (ret) {
> +		dev_err(dev, "Failed to init buffer, ret = %d\n", ret);
> +		return ret;
> +	}
> +
> +	smb_init_hw(drvdata);
> +	mutex_init(&drvdata->mutex);
> +	drvdata->pid = -1;
> +
> +	ret = smb_register_sink(pdev, drvdata);
> +	if (ret) {
> +		dev_err(dev, "Failed to register SMB sink\n");
> +		return ret;
> +	}
> +
> +	ret = smb_config_inport(dev, true);
> +	if (ret) {
> +		smb_unregister_sink(drvdata);
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, drvdata);
> +
> +	return 0;
> +}
> +
> +static int smb_remove(struct platform_device *pdev)
> +{
> +	struct smb_drv_data *drvdata = platform_get_drvdata(pdev);
> +	int ret;
> +
> +	ret = smb_config_inport(&pdev->dev, false);
> +	if (ret)
> +		return ret;
> +
> +	smb_unregister_sink(drvdata);
> +
> +	return 0;
> +}
> +
> +static const struct acpi_device_id ultrasoc_smb_acpi_match[] = {
> +	{"HISI03A1", 0},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(acpi, ultrasoc_smb_acpi_match);
> +
> +static struct platform_driver smb_driver = {
> +	.driver = {
> +		.name = "ultrasoc-smb",
> +		.acpi_match_table = ACPI_PTR(ultrasoc_smb_acpi_match),
> +		.suppress_bind_attrs = true,
> +	},
> +	.probe = smb_probe,
> +	.remove = smb_remove,
> +};
> +module_platform_driver(smb_driver);
> +
> +MODULE_DESCRIPTION("UltraSoc SMB CoreSight driver");
> +MODULE_LICENSE("Dual MIT/GPL");
> +MODULE_AUTHOR("Jonathan Zhou <jonathan.zhouwen@huawei.com>");
> +MODULE_AUTHOR("Qi Liu <liuqi115@huawei.com>");
> diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.h b/drivers/hwtracing/coresight/ultrasoc-smb.h
> new file mode 100644
> index 000000000000..2e2f9f8fe54b
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/ultrasoc-smb.h
> @@ -0,0 +1,116 @@
> +/* SPDX-License-Identifier: (GPL-2.0 OR MIT) */
> +/*
> + * Siemens System Memory Buffer driver.
> + * Copyright(c) 2022, HiSilicon Limited.
> + */
> +
> +#ifndef _ULTRASOC_SMB_H
> +#define _ULTRASOC_SMB_H
> +
> +#include <linux/miscdevice.h>
> +#include <linux/mutex.h>
> +
> +/* Offset of SMB global registers */
> +#define SMB_GLB_CFG_REG		0x00
> +#define SMB_GLB_EN_REG		0x04
> +#define SMB_GLB_INT_REG		0x08
> +
> +/* Offset of SMB logical buffer registers */
> +#define SMB_LB_CFG_LO_REG	0x40
> +#define SMB_LB_CFG_HI_REG	0x44
> +#define SMB_LB_INT_CTRL_REG	0x48
> +#define SMB_LB_INT_STS_REG	0x4c
> +#define SMB_LB_RD_ADDR_REG	0x5c
> +#define SMB_LB_WR_ADDR_REG	0x60
> +#define SMB_LB_PURGE_REG	0x64
> +
> +/* Set global config register */
> +#define SMB_CFG_BURST_LEN_MSK	GENMASK(11, 4)
> +#define SMB_CFG_IDLE_PRD_MSK	GENMASK(15, 12)
> +#define SMB_CFG_MEM_WR_MSK	GENMASK(21, 16)
> +#define SMB_CFG_MEM_RD_MSK	GENMASK(27, 22)
> +#define SMB_GLB_CFG_DEFAULT	(FIELD_PREP(SMB_CFG_BURST_LEN_MSK, 0xf) | \
> +				 FIELD_PREP(SMB_CFG_IDLE_PRD_MSK, 0xf) | \
> +				 FIELD_PREP(SMB_CFG_MEM_WR_MSK, 0x3) | \
> +				 FIELD_PREP(SMB_CFG_MEM_RD_MSK, 0x1b))
> +
> +/* Set global interrupt control register */
> +#define SMB_INT_EN		BIT(0)
> +#define SMB_INT_PULSE		BIT(1) /* Interrupt type: 1 - Pulse */
> +#define SMB_INT_ACT_H		BIT(2) /* Interrupt polarity: 1 - Active high */
> +#define SMB_GLB_INT_CFG		(SMB_INT_EN | SMB_INT_PULSE | SMB_INT_ACT_H)
> +
> +/* Set logical buffer config register lower 32 bits */
> +#define SMB_CFG_LO_EN		BIT(0)
> +#define SMB_CFG_LO_SINGLE_END	BIT(1)
> +#define SMB_CFG_LO_INIT		BIT(8)
> +#define SMB_CFG_LO_CONT		BIT(11)
> +#define SMB_CFG_LO_FLOW_MSK	GENMASK(19, 16)
> +#define SMB_LB_CFG_LO_DEFAULT	(SMB_CFG_LO_EN | SMB_CFG_LO_SINGLE_END | \
> +				 SMB_CFG_LO_INIT | SMB_CFG_LO_CONT | \
> +				 FIELD_PREP(SMB_CFG_LO_FLOW_MSK, 0xf))
> +
> +/* Set logical buffer config register upper 32 bits */
> +#define SMB_CFG_HI_RANGE_UP_MSK	GENMASK(15, 8)
> +#define SMB_LB_CFG_HI_DEFAULT	FIELD_PREP(SMB_CFG_HI_RANGE_UP_MSK, 0xff)
> +
> +/* Set logical buffer interrupt control register */
> +#define SMB_INT_CTRL_EN			BIT(0)
> +#define SMB_INT_CTRL_BUF_NOTE_MSK	GENMASK(11, 8)
> +#define SMB_LB_INT_CTRL_CFG	(SMB_INT_CTRL_EN | \
> +				 FIELD_PREP(SMB_INT_CTRL_BUF_NOTE_MSK, 0xf))
> +
> +#define SMB_LB_INT_STS_NOT_EMPTY_MSK	BIT(0)
> +#define SMB_LB_STS_RESET_MSK		GENMASK(3, 0)
> +#define SMB_LB_INT_BUF_STS_RESET	FIELD_PREP(SMB_LB_STS_RESET_MSK, 0xf)
> +#define SMB_LB_PURGE_PURGED	BIT(0)
> +#define SMB_GLB_EN_HW_ENABLE	BIT(0)
> +
> +#define SMB_REG_ADDR_RES	0
> +#define SMB_BUF_ADDR_RES	1
> +#define SMB_BUF_ADDR_LO_MSK	GENMASK(31, 0)
> +
> +/**
> + * struct smb_data_buffer - Details of the buffer used by SMB
> + * @buf_base:	Memory mapped base address of SMB.
> + * @start_addr:	SMB buffer start Physical address.
> + * @buf_size:	Size of the buffer.
> + * @data_size:	Size of Trace data copy to userspace.
> + * @rd_offset:	Offset of the read pointer in the buffer.
> + * @wr_offset:	Offset of the write pointer in the buffer.
> + * @full:	Trace data overflow.
> + */
> +struct smb_data_buffer {
> +	void __iomem *buf_base;

The backend of buffer is a chunk of memory, so I guess we don't need
this __iomem here.

> +	u32 start_addr;

Is u32 enough if we're running on a 64bit platform? You can use phys_addr_t
instead since you comment it to be "start Physical address".

> +	unsigned long buf_size;
> +	unsigned long data_size;
> +	unsigned long rd_offset;
> +	unsigned long wr_offset;
> +	bool full;
> +};
> +
> +/**
> + * struct smb_drv_data - specifics associated to an SMB component
> + * @base:	Memory mapped base address for SMB component.
> + * @csdev:	Component vitals needed by the framework.
> + * @sdb:	Data buffer for SMB.
> + * @miscdev:	Specifics to handle "/dev/xyz.smb" entry.
> + * @mutex:	Control data access to one at a time.
> + * @reading:	Synchronise user space access to SMB buffer.
> + * @pid:	Process ID of the process being monitored by the
> + *		session that is using this component.
> + * @mode:	how this SMB is being used, perf mode or sysfs mode.
> + */
> +struct smb_drv_data {
> +	void __iomem *base;
> +	struct coresight_device	*csdev;
> +	struct smb_data_buffer sdb;
> +	struct miscdevice miscdev;
> +	struct mutex mutex;
> +	local_t reading;

Why do we need to use local_t here? Considering the whole structure is
already protected by the mutex, maybe a boolean is enough?

Thanks.