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Message-ID: <da88a7eb-00e6-0a87-5fbf-99d5c72f28a9@arm.com>
Date:   Wed, 9 Mar 2022 22:49:23 +0000
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Subject: Re: [PATCH v4] drivers/coresight: Add Ultrasoc System Memory Buffer
 driver
To:     Qi Liu <liuqi115@huawei.com>, mathieu.poirier@linaro.org,
        mike.leach@linaro.org
Cc:     coresight@lists.linaro.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linuxarm@huawei.com
References: <20220128061755.31909-1-liuqi115@huawei.com>
From:   Suzuki K Poulose <suzuki.poulose@arm.com>
In-Reply-To: <20220128061755.31909-1-liuqi115@huawei.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi

On 28/01/2022 06:17, Qi Liu wrote:
> 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 in system memory.
> 
> SMB is developed by Ultrasoc technology, which is acquired by
> Siemens, and we still use "Ultrasoc" to name driver.
> 
> Signed-off-by: Qi Liu <liuqi115@huawei.com>
> Tested-by: JunHao He <hejunhao2@hisilicon.com>

Please find my comments below. In general :

1) Please run checkpatch and fix the warnings
2) Add documentation for :
      - A brief description of the device and the firmware bindings (see 
comments below )
      - Sysfs attributes
3) Other minor comments on the code

> ---
> Change since v3:
> - Modify the file header according to community specifications.
> - Address the comments from Mathieu.
> - Link:https://lore.kernel.org/linux-arm-kernel/20211118110016.40398-1-liuqi115@huawei.com/
> Change since v2:
> - Move ultrasoc driver to drivers/hwtracing/coresight.
> - Link:https://lists.linaro.org/pipermail/coresight/2021-November/007310.html
> 
> Change since v1:
> - Drop the document of Ultrasoc according to Mathieu's comment.
> - Add comments to explain some private hardware settings.
> - Address the comments from Mathieu.
> - Link: https://lists.linaro.org/pipermail/coresight/2021-August/006842.html
> 
> Change since RFC:
> - Move ultrasoc driver to drivers/hwtracing/coresight/ultrasoc.
> - Remove ultrasoc-axi-com.c, as AXI-COM doesn't need to be configured in
>    basic tracing function.
> - Remove ultrasoc.c as SMB does not need to register with the ultrasoc core.
> - Address the comments from Mathieu and Suzuki.
> - Link: https://lists.linaro.org/pipermail/coresight/2021-June/006535.html
> 
>   drivers/hwtracing/coresight/Kconfig        |  10 +
>   drivers/hwtracing/coresight/Makefile       |   1 +
>   drivers/hwtracing/coresight/ultrasoc-smb.c | 602 +++++++++++++++++++++
>   drivers/hwtracing/coresight/ultrasoc-smb.h | 100 ++++
>   4 files changed, 713 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 514a9b8086e3..32b87df9994a 100644
> --- a/drivers/hwtracing/coresight/Kconfig
> +++ b/drivers/hwtracing/coresight/Kconfig
> @@ -201,4 +201,14 @@ 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

Given that this driver absolutely only works with ACPI, please could
you add that dependency here ?

> +	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..a18d061aab61
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/ultrasoc-smb.c
> @@ -0,0 +1,602 @@
> +// SPDX-License-Identifier: MIT/GPL
> +/*
> + * Siemens System Memory Buffer driver.
> + * Copyright(c) 2022, HiSilicon Limited.
> + */
> +
> +#include <linux/acpi.h>
> +#include <linux/circ_buf.h>
> +#include <linux/err.h>
> +#include <linux/module.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/platform_device.h>
> +
> +#include "ultrasoc-smb.h"
> +
> +DEFINE_CORESIGHT_DEVLIST(sink_devs, "smb");

minor nit: This name could be confused with SMB (samba) under linux
especially when it appears under /dev/smbN as a misc device.

> +
> +static bool smb_buffer_is_empty(struct smb_drv_data *drvdata)
> +{
> +	u32 buf_status = readl(drvdata->base + SMB_LB_INT_STS);
> +
> +	return buf_status & BIT(0) ? false : true;
> +}
> +
> +static bool smb_buffer_cmp_pointer(struct smb_drv_data *drvdata)
> +{
> +	u32 wr_offset, rd_offset;
> +
> +	wr_offset = readl(drvdata->base + SMB_LB_WR_ADDR);
> +	rd_offset = readl(drvdata->base + SMB_LB_RD_ADDR);
> +	return wr_offset == rd_offset;
> +}
> +
> +static void smb_reset_buffer_status(struct smb_drv_data *drvdata)
> +{
> +	writel(0xf, drvdata->base + SMB_LB_INT_STS);
> +}
> +
> +/* Purge data remaining in hardware path to SMB. */
> +static void smb_purge_data(struct smb_drv_data *drvdata)
> +{
> +	writel(0x1, drvdata->base + SMB_LB_PURGE);
> +}
> +
> +static void smb_update_data_size(struct smb_drv_data *drvdata)
> +{
> +	struct smb_data_buffer *sdb = &drvdata->sdb;
> +	u32 write_offset;
> +
> +	smb_purge_data(drvdata);
> +	if (smb_buffer_cmp_pointer(drvdata)) {
> +		if (smb_buffer_is_empty(drvdata))
> +			sdb->data_size = 0;
> +		else
> +			sdb->data_size = sdb->buf_size;
> +		return;
> +	}
> +
> +	write_offset = readl(drvdata->base + SMB_LB_WR_ADDR) - sdb->start_addr;
> +	sdb->data_size = CIRC_CNT(write_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);
> +
> +	if (local_cmpxchg(&drvdata->reading, 0, 1))
> +		return -EBUSY;
> +
> +	return 0;
> +}
> +
> +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;
> +	unsigned long flags;
> +	int to_copy = 0;
> +
> +	spin_lock_irqsave(&drvdata->spinlock, flags);
> +
> +	if (!sdb->data_size) {
> +		smb_update_data_size(drvdata);
> +		if (!sdb->data_size)
> +			goto out;
> +	}
> +
> +	if (atomic_read(drvdata->csdev->refcnt)) {
> +		to_copy = -EBUSY;
> +		goto out;
> +	}
> +

Shouldn't this be performed *before* updating the data_size above ?
Looking at the smb_update_data_size() it "purges" the data. Is that
acceptable ?

> +	to_copy = min(sdb->data_size, len);
> +
> +	/* Copy parts of trace data when the read pointer will 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);
> +	dev_dbg(dev, "%d bytes copied\n", to_copy);
> +out:
> +	if (!sdb->data_size)
> +		smb_reset_buffer_status(drvdata);
> +	spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +	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);
> +	local_set(&drvdata->reading, 0);
> +	return 0;
> +}
> +
> +static const struct file_operations smb_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= smb_open,
> +	.read		= smb_read,
> +	.release	= smb_release,
> +	.llseek		= no_llseek,
> +};
> +
> +smb_reg(read_pos, SMB_LB_RD_ADDR);
> +smb_reg(write_pos, SMB_LB_WR_ADDR);
> +smb_reg(buf_status, SMB_LB_INT_STS);
> +
> +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);
> +}
> +static DEVICE_ATTR_RO(buf_size);
> +
> +static struct attribute *smb_sink_attrs[] = {
> +	&dev_attr_read_pos.attr,
> +	&dev_attr_write_pos.attr,
> +	&dev_attr_buf_status.attr,
> +	&dev_attr_buf_size.attr,
> +	NULL,
> +};

Please could you also update the sysfs ABI files with a brief
description of the above attributes ?

e.g., Documentation/ABI/testing/sysfs-bus-coresight-devices-tmc

> +
> +static const struct attribute_group smb_sink_group = {
> +	.attrs = smb_sink_attrs,
> +	.name = "status",
> +};
> +
> +static const struct attribute_group *smb_sink_groups[] = {
> +	&smb_sink_group,
> +	NULL,
> +};
> +
> +static int smb_set_perf_buffer(struct perf_output_handle *handle)
> +{
> +	struct cs_buffers *buf = etm_perf_sink_config(handle);
> +	u32 head;
> +
> +	if (!buf)
> +		return -EINVAL;
> +
> +	/* Wrap head around to the amount of space we have */
> +	head = handle->head & ((buf->nr_pages << PAGE_SHIFT) - 1);
> +
> +	/* Find the page to write to and offset within that page */
> +	buf->cur = head / PAGE_SIZE;
> +	buf->offset = head % PAGE_SIZE;
> +
> +	local_set(&buf->data_size, 0);
> +
> +	return 0;
> +}
> +
> +static void smb_enable_hw(struct smb_drv_data *drvdata)
> +{
> +	writel(0x1, drvdata->base + SMB_GLOBAL_EN);
> +}
> +
> +static void smb_disable_hw(struct smb_drv_data *drvdata)
> +{
> +	writel(0x0, drvdata->base + SMB_GLOBAL_EN);
> +}
> +
> +static int smb_enable_sysfs(struct smb_drv_data *drvdata)
> +{
> +	if (drvdata->mode == CS_MODE_PERF)
> +		return -EBUSY;
> +
> +	if (drvdata->mode == CS_MODE_SYSFS)
> +		return 0;
> +
> +	smb_enable_hw(drvdata);
> +	drvdata->mode = CS_MODE_SYSFS;
> +	return 0;
> +}
> +
> +static int smb_enable_perf(struct smb_drv_data *drvdata, void *data)
> +{
> +	struct device *dev = &drvdata->csdev->dev;
> +	struct perf_output_handle *handle = data;
> +	pid_t pid;
> +
> +	if (drvdata->mode == CS_MODE_SYSFS) {
> +		dev_err(dev, "Device is already in used by sysfs\n");

Please could you convert this to dev_dbg() ? An -EBUSY should
be sufficient to indicate that the resource is busy.

> +		return -EBUSY;
> +	}
> +
> +	/* Get a handle on the pid of the target process*/
> +	pid = task_pid_nr(handle->event->owner);
> +	if (drvdata->pid != -1 && drvdata->pid != pid) {
> +		dev_err(dev, "Device is already in used by other session\n");

Same here.

> +		return -EBUSY;
> +	}
> +	/* The sink is already enabled by this session. */
> +	if (drvdata->pid == pid)
> +		return 0;

If the sink is shared by multiple events of the same group, don't
we need a refcount to make sure we don't disable the buffer when
an event goes away ?

> +
> +	if (smb_set_perf_buffer(handle))
> +		return -EINVAL;
> +
> +	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);
> +	unsigned long flags;
> +	int ret = -EINVAL;
> +
> +	/* Do nothing if trace data is reading by other interface now. */
> +	if (local_read(&drvdata->reading))
> +		return -EBUSY;
> +
> +	spin_lock_irqsave(&drvdata->spinlock, flags);
> +
> +	if (mode == CS_MODE_SYSFS)
> +		ret = smb_enable_sysfs(drvdata);
> +
> +	if (mode == CS_MODE_PERF)
> +		ret = smb_enable_perf(drvdata, data);
> +
> +	spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +
> +	if (ret)
> +		return ret;
> +
> +	atomic_inc(csdev->refcnt);
> +	dev_dbg(&csdev->dev, "Ultrasoc SMB enabled\n");
> +
> +	return 0;
> +}
> +
> +static int smb_disable(struct coresight_device *csdev)
> +{
> +	struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&drvdata->spinlock, flags);
> +
> +	if (atomic_dec_return(csdev->refcnt)) {

We need to increment the refcnt for every event that shares the
sink for perf mode. Please see my comments above.

> +		spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +		return -EBUSY;
> +	}
> +
> +	WARN_ON_ONCE(drvdata->mode == CS_MODE_DISABLED);
> +	smb_disable_hw(drvdata);
> +
> +	/*
> +	 * Data remaining in hardware path will be sent to SMB after purge, so needs to
> +	 * synchronize the read pointer to write pointer in perf mode.

Please run checkpatch on your submission ^^^


> +	 */
> +	smb_purge_data(drvdata);
> +	if (drvdata->mode == CS_MODE_PERF)
> +		writel(readl(drvdata->base + SMB_LB_WR_ADDR), drvdata->base + SMB_LB_RD_ADDR);

Same here. Why don't we do this for CS_MODE_SYSFS ?

> +
> +	/* Dissociate from the target process. */
> +	drvdata->pid = -1;
> +	drvdata->mode = CS_MODE_DISABLED;
> +	spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +
> +	dev_dbg(&csdev->dev, "Ultrasoc SMB disabled\n");
> +	return 0;
> +}
> +
> +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(*buf), GFP_KERNEL, node);
> +	if (!buf)
> +		return NULL;
> +
> +	buf->snapshot = overwrite;
> +	buf->nr_pages = nr_pages;
> +	buf->data_pages = pages;
> +
> +	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 data_size)
> +{
> +	struct smb_data_buffer *sdb = &drvdata->sdb;
> +	char **dst_pages = (char **)buf->data_pages;
> +	unsigned long buf_offset = buf->offset;

Please could you rename this to page_offset ?

> +	unsigned int cur = buf->cur;
> +	unsigned long to_copy;
> +

> +	while (data_size) {
> +		/* Copy parts of trace data when the read pointer will wrap around SMB buffer. */

Wrap the lines please.

Please could you do :

		unsigned long page_space = (PAGE_SIZE - page_offset);


> +		if (sdb->rd_offset + PAGE_SIZE - buf_offset > sdb->buf_size)

^^		if (sdb->rd_offset + page_space > sdb->buf_size)

> +			to_copy = sdb->buf_size - sdb->rd_offset;
> +		else
> +			to_copy = min(data_size, PAGE_SIZE - buf_offset);

			to_copy = min(data_size, page_space);

> +
> +		memcpy_fromio(dst_pages[cur] + buf_offset, sdb->buf_base + sdb->rd_offset, to_copy);

		memcpy_fromio(dst_pages[cur] + page_offset, ...

> +
> +		buf_offset += to_copy;
> +		if (buf_offset >= PAGE_SIZE) {

That becomes much simpler to follow with the rename to page_offset.

> +			buf_offset = 0;
> +			cur++;
> +			cur %= buf->nr_pages;
> +		}
> +		data_size -= to_copy;
> +		/* ensure memcpy finished before update the read pointer */

Why and how ?

> +		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);
> +	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;
> +	unsigned long flags;
> +	bool lost = false;
> +
> +	if (!buf)
> +		return 0;
> +
> +	spin_lock_irqsave(&drvdata->spinlock, flags);
> +
> +	/* Don't do anything if another tracer is using this sink. */
> +	if (atomic_read(csdev->refcnt) != 1)
> +		goto out;
> +
> +	smb_update_data_size(drvdata);
> +	data_size = sdb->data_size;

Please could you add in a comment on what we do here below ?

> +	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, data_size);
> +	if (!buf->snapshot && lost)
> +		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
> +
> +out:
> +	spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +	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, 1);

What are these IO bases ? What does 0 stand for ? What is 1 for ?

Please could you add a documentation under

Documentation/trace/coresight/.

Doesn't need to be too detailed. But a basic description would be helpful.


> +	if (IS_ERR(res)) {
> +		dev_err(&pdev->dev, "SMB device failed to get resource\n");
> +		return -EINVAL;
> +	}
> +
> +	sdb->start_addr = res->start & SMB_BASE_LOW_MASK;
> +	sdb->buf_size = resource_size(res);
> +	if (sdb->buf_size == 0)
> +		return -EINVAL;
> +
> +	base = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(base))
> +		return PTR_ERR(base);
> +
> +	sdb->buf_base = base;
> +
> +	return 0;
> +}
> +
> +static void smb_init_hw(struct smb_drv_data *drvdata)
> +{
> +	u32 value;
> +
> +	/* First disable smb and clear the status of SMB buffer */
> +	smb_reset_buffer_status(drvdata);
> +	smb_disable_hw(drvdata);
> +	smb_purge_data(drvdata);
> +
> +	/* Using smb in single-end mode, and set other configures default */
> +	value = SMB_BUF_CFG_STREAMING | SMB_BUF_SINGLE_END | SMB_BUF_EN;
> +	writel(value, drvdata->base + SMB_LB_CFG_LO);
> +	value = SMB_MSG_FILTER(0x0, 0xff);

Could we not simply say :


> +	writel(value, drvdata->base + SMB_LB_CFG_HI);
> +

	#define SMB_CFG_MSG_FILTER	0xff00

	writel(SMB_CFG_MSG_FILTER, drvdata->base + SMB_LB_CFG_HI) ?


Just like you do below for the other registers ? Anyways, none of these
values make any sense to the reader without the Reference Manual. The
best you could do is stick a sensible name for the value like you do
below.

> +	writel(SMB_GLOBAL_CFG, drvdata->base + SMB_CFG_REG);
> +	writel(SMB_GLB_INT_CFG, drvdata->base + SMB_GLOBAL_INT);
> +	writel(SMB_BUF_INT_CFG, drvdata->base + SMB_LB_INT_CTRL);
> +}
> +
> +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;
> +	}
> +
> +	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: %d\n", ret);
> +	}
> +
> +	return ret;
> +}
> +
> +static void smb_unregister_sink(struct smb_drv_data *drvdata)
> +{
> +	misc_deregister(&drvdata->miscdev);
> +	coresight_unregister(drvdata->csdev);
> +}
> +
> +/*
> + * Send ultrasoc messge to control hardwares on the tracing path,
> + * using DSM calls to avoid exposing ultrasoc message format.
> + */
> +static int smb_config_inport(struct device *dev, bool enable)
> +{
> +	u32 flag = enable ? 1 : 0;
> +	union acpi_object *obj;
> +	guid_t guid;
> +
> +	if (guid_parse("82ae1283-7f6a-4cbe-aa06-53e8fb24db18", &guid)) {

Please could you add symbolic name for this UUID string and a comment on
what this will do ?

> +		dev_err(dev, "Get GUID failed\n");
> +		return -EINVAL;
> +	}
> +
> +	obj = acpi_evaluate_dsm(ACPI_HANDLE(dev), &guid, 0, flag, NULL);

What are the parameters ? What do they mean ?

> +	if (!obj)
> +		dev_err(dev, "ACPI handle failed\n");
> +	else
> +		ACPI_FREE(obj);
> +
> +	return 0;
> +}
> +
> +static int smb_probe(struct platform_device *pdev)
> +{
> +	struct smb_drv_data *drvdata;
> +	int ret;
> +
> +	drvdata = devm_kzalloc(&pdev->dev, sizeof(*drvdata), GFP_KERNEL);
> +	if (!drvdata)
> +		return -ENOMEM;
> +
> +	drvdata->base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(drvdata->base)) {
> +		dev_err(&pdev->dev, "Failed to ioremap resource\n");
> +		return PTR_ERR(drvdata->base);
> +	}
> +
> +	ret = smb_init_data_buffer(pdev, &drvdata->sdb);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Failed to init buffer: %d\n", ret);
> +		return ret;
> +	}
> +
> +	smb_init_hw(drvdata);
> +	spin_lock_init(&drvdata->spinlock);
> +	drvdata->pid = -1;
> +
> +	ret = smb_register_sink(pdev, drvdata);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Failed to register smb sink\n");
> +		return ret;
> +	}
> +
> +	ret = smb_config_inport(&pdev->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;
> +}
> +
> +#ifdef CONFIG_ACPI
> +static const struct acpi_device_id ultrasoc_smb_acpi_match[] = {
> +	{"HISI03A1", 0},
> +	{},
> +};
> +MODULE_DEVICE_TABLE(acpi, ultrasoc_smb_acpi_match);
> +#endif

As mentioned above this driver must depend on the ACPI and thus
you may remove the #ifdef

> +
> +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 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..a7c76140ee46
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/ultrasoc-smb.h
> @@ -0,0 +1,100 @@
> +/* SPDX-License-Identifier: MIT */
> +/*
> + * Siemens System Memory Buffer driver.
> + * Copyright(c) 2022, HiSilicon Limited.
> + */
> +
> +#ifndef _ULTRASOC_SMB_H
> +#define _ULTRASOC_SMB_H
> +
> +#include <linux/coresight.h>
> +#include <linux/list.h>
> +#include <linux/miscdevice.h>
> +
> +#include "coresight-etm-perf.h"
> +#include "coresight-priv.h"
> +
> +/* Offset of SMB logical buffer registers */
> +#define SMB_CFG_REG			0X0
> +#define SMB_GLOBAL_EN			0X4
> +#define SMB_GLOBAL_INT			0X8
> +#define SMB_LB_CFG_LO			0X40
> +#define SMB_LB_CFG_HI			0X44
> +#define SMB_LB_INT_CTRL			0X48
> +#define SMB_LB_INT_STS			0X4C
> +#define SMB_LB_LIMIT			0X58
> +#define SMB_LB_RD_ADDR			0X5C
> +#define SMB_LB_WR_ADDR			0X60
> +#define SMB_LB_PURGE			0X64
> +
> +/* Set SMB_CFG_REG register */
> +#define SMB_IDLE_PRD(period)		((((period) - 216) & 0xf) << 12)
> +#define SMB_MEM_WR(credit, rate)	(((credit) << 16) | ((rate) << 18))
> +#define SMB_MEM_RD(credit, rate)	(((credit) << 22) | ((rate) << 24))
> +#define SMB_BURST_LEN(len)		(((len) - 1) << 4)
> +#define SMB_GLOBAL_CFG			(SMB_IDLE_PRD(231) | SMB_MEM_WR(0x3, 0x0) |   \
> +					 SMB_MEM_RD(0x3, 0x6) | SMB_BURST_LEN(16))
> +
> +/* Set SMB_GLOBAL_INT register */
> +#define SMB_INT_EN			BIT(0)
> +#define SMB_INT_TYPE_PULSE		BIT(1)
> +#define SMB_INT_POLARITY_HIGH		BIT(2)
> +#define SMB_GLB_INT_CFG			(SMB_INT_EN | SMB_INT_TYPE_PULSE | SMB_INT_POLARITY_HIGH)
> +
> +/* Set SMB_LB_CFG_LO register */
> +#define SMB_BUF_EN			BIT(0)
> +#define SMB_BUF_SINGLE_END		BIT(1)
> +#define SMB_BUF_INIT			BIT(8)
> +#define SMB_BUF_CONTINUOUS		BIT(11)
> +#define SMB_FLOW_MASK			GENMASK(19, 16)
> +#define SMB_BUF_CFG_STREAMING		(SMB_BUF_INIT | SMB_BUF_CONTINUOUS | SMB_FLOW_MASK)
> +#define SMB_BASE_LOW_MASK		GENMASK(31, 0)
> +
> +/* Set SMB_LB_CFG_HI register */
> +#define SMB_MSG_FILTER(lower, upper)	(((lower) & 0xff) | (((upper) & 0xff) << 8))

There is only one place where this is used and it is unnecessarily
confusing. Why not simply define:

#define SMB_CFG_MSG_FILTER		0xff00


> +#define SMB_BUF_INT_EN			BIT(0)
> +#define SMB_BUF_NOTE_MASK		GENMASK(11, 8)
> +#define SMB_BUF_INT_CFG			(SMB_BUF_INT_EN | SMB_BUF_NOTE_MASK)
> +
> +/**
> + * 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.
> + */
> +struct smb_data_buffer {
> +	void __iomem *buf_base;
> +	u32 start_addr;
> +	unsigned long buf_size;
> +	unsigned long data_size;
> +	unsigned long rd_offset;
> +};
> +
> +/**
> + * 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/smb" entry.
> + * @spinlock	: Only one at a time pls.
> + * @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;
> +	spinlock_t spinlock;
> +	local_t reading;
> +	pid_t pid;
> +	u32 mode;
> +};
> +
> +#define smb_reg(name, offset)  coresight_simple_reg32(struct smb_drv_data, name, offset)
> +
> +#endif

Suzuki