[3/3] interconnect: Add debugfs test client

It's often useful during test, debug, and development to issue path
votes from shell. Add a debugfs client for this purpose.

Example usage:
	cd /sys/kernel/debug/interconnect/test-client/

	# Configure node endpoints for the path from CPU to DDR on
	# qcom/sm8550.
	echo chm_apps > src_node
	echo ebi > dst_node

	# Get path between src_node and dst_node. This is only
	# necessary after updating the node endpoints.
	echo 1 > get

	# Set desired BW to 1GBps avg and 2GBps peak.
	echo 1000000 > avg_bw
	echo 2000000 > peak_bw

	# Vote for avg_bw and peak_bw on the latest path from "get".
	# Voting for multiple paths is possible by repeating this
	# process for different nodes endpoints.
	echo 1 > commit

Allowing userspace to directly enable and set bus rates can be dangerous
So, following in the footsteps of the regmap [0] and clk [1] frameworks,
keep these userspace controls compile-time disabled without Kconfig
options to enable them. Enabling this will require code changes to
define INTERCONNECT_ALLOW_WRITE_DEBUGFS.

[0] commit 09c6ecd39410 ("regmap: Add support for writing to regmap registers via debugfs")
[1] commit 37215da5553e ("clk: Add support for setting clk_rate via debugfs")

Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
---
 drivers/interconnect/Makefile         |   2 +-
 drivers/interconnect/core.c           |   3 +
 drivers/interconnect/debugfs-client.c | 156 ++++++++++++++++++++++++++
 drivers/interconnect/internal.h       |   2 +
 4 files changed, 162 insertions(+), 1 deletion(-)
 create mode 100644 drivers/interconnect/debugfs-client.c

On Mon, Jul 24, 2023 at 06:28:59PM -0700, Mike Tipton wrote:
> It's often useful during test, debug, and development to issue path
> votes from shell. Add a debugfs client for this purpose.
> 
> Example usage:
> 	cd /sys/kernel/debug/interconnect/test-client/
> 
> 	# Configure node endpoints for the path from CPU to DDR on
> 	# qcom/sm8550.
> 	echo chm_apps > src_node
> 	echo ebi > dst_node
> 
> 	# Get path between src_node and dst_node. This is only
> 	# necessary after updating the node endpoints.
> 	echo 1 > get
> 
> 	# Set desired BW to 1GBps avg and 2GBps peak.
> 	echo 1000000 > avg_bw
> 	echo 2000000 > peak_bw
> 
> 	# Vote for avg_bw and peak_bw on the latest path from "get".
> 	# Voting for multiple paths is possible by repeating this
> 	# process for different nodes endpoints.
> 	echo 1 > commit
> 

Can Documentation/driver-api/interconnect.rst be updated with this
information?

> Allowing userspace to directly enable and set bus rates can be dangerous
> So, following in the footsteps of the regmap [0] and clk [1] frameworks,
> keep these userspace controls compile-time disabled without Kconfig
> options to enable them. Enabling this will require code changes to
> define INTERCONNECT_ALLOW_WRITE_DEBUGFS.
>  

Completely agree with your argument here.

> [0] commit 09c6ecd39410 ("regmap: Add support for writing to regmap registers via debugfs")
> [1] commit 37215da5553e ("clk: Add support for setting clk_rate via debugfs")
> 
> Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
> ---
>  drivers/interconnect/Makefile         |   2 +-
>  drivers/interconnect/core.c           |   3 +
>  drivers/interconnect/debugfs-client.c | 156 ++++++++++++++++++++++++++
>  drivers/interconnect/internal.h       |   2 +
>  4 files changed, 162 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/interconnect/debugfs-client.c
> 
> diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
> index 5604ce351a9f..d0888babb9a1 100644
> --- a/drivers/interconnect/Makefile
> +++ b/drivers/interconnect/Makefile
> @@ -1,7 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  CFLAGS_core.o				:= -I$(src)
> -icc-core-objs				:= core.o bulk.o
> +icc-core-objs				:= core.o bulk.o debugfs-client.o
>  
>  obj-$(CONFIG_INTERCONNECT)		+= icc-core.o
>  obj-$(CONFIG_INTERCONNECT_IMX)		+= imx/
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> index 511152398790..bc82571ff2a8 100644
> --- a/drivers/interconnect/core.c
> +++ b/drivers/interconnect/core.c
> @@ -1117,6 +1117,9 @@ static int __init icc_init(void)
>  			    icc_debugfs_dir, NULL, &icc_summary_fops);
>  	debugfs_create_file("interconnect_graph", 0444,
>  			    icc_debugfs_dir, NULL, &icc_graph_fops);
> +
> +	icc_debugfs_client_init(icc_debugfs_dir);
> +
>  	return 0;
>  }
>  
> diff --git a/drivers/interconnect/debugfs-client.c b/drivers/interconnect/debugfs-client.c
> new file mode 100644
> index 000000000000..990dd2ff6df7
> --- /dev/null
> +++ b/drivers/interconnect/debugfs-client.c
> @@ -0,0 +1,156 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2023, Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +#include <linux/debugfs.h>
> +#include <linux/interconnect.h>
> +#include <linux/platform_device.h>
> +#include <linux/uaccess.h>
> +

Since you are not dealing with user copy directly, I wonder why this
header inclusion is needed?

> +/*
> + * This can be dangerous, therefore don't provide any real compile time
> + * configuration option for this feature.
> + * People who want to use this will need to modify the source code directly.
> + */
> +#undef INTERCONNECT_ALLOW_WRITE_DEBUGFS
> +

Would it be nice to throw a compile error when DEBUG_FS is not enabled
but INTERCONNECT_ALLOW_WRITE_DEBUGFS is enabled?

> +#if defined(INTERCONNECT_ALLOW_WRITE_DEBUGFS) && defined(CONFIG_DEBUG_FS)
> +
> +static LIST_HEAD(debugfs_paths);
> +static DEFINE_MUTEX(debugfs_lock);
> +
> +static struct platform_device *pdev;
> +static struct icc_path *cur_path;
> +
> +static char *src_node;
> +static char *dst_node;
> +static u32 avg_bw;
> +static u32 peak_bw;
> +static u32 tag;
> +
> +struct debugfs_path {
> +	const char *src;
> +	const char *dst;
> +	struct icc_path *path;
> +	struct list_head list;
> +};
> +
> +static struct icc_path *get_path(const char *src, const char *dst)
> +{
> +	struct debugfs_path *path;
> +
> +	list_for_each_entry(path, &debugfs_paths, list) {
> +		if (!strcmp(path->src, src) && !strcmp(path->dst, dst))
> +			return path->path;
> +	}
> +
> +	return NULL;
> +}
> +
> +static int icc_get_set(void *data, u64 val)
> +{
> +	struct debugfs_path *debugfs_path;
> +	int ret = 0;
> +
> +	mutex_lock(&debugfs_lock);
> +
> +	/*
> +	 * If we've already looked up a path, then use the existing one instead
> +	 * of calling icc_get() again. This allows for updating previous BW
> +	 * votes when "get" is written to multiple times for multiple paths.
> +	 */
> +	cur_path = get_path(src_node, dst_node);
> +	if (cur_path)
> +		goto out;
> +
> +	cur_path = icc_get(&pdev->dev, src_node, dst_node);
> +	if (IS_ERR(cur_path)) {
> +		ret = PTR_ERR(cur_path);
> +		goto out;
> +	}