linux-kernel - Re: [PATCH v2 5/5] apple-gmux: add debugfs interface

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Message-ID: <0a58bf19-d943-b8c6-a882-7209d0543823@redhat.com>
Date:   Thu, 16 Feb 2023 14:20:27 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Orlando Chamberlain <orlandoch.dev@...il.com>
Cc:     Mark Gross <markgross@...nel.org>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lukas Wunner <lukas@...ner.de>,
        Seth Forshee <sforshee@...nel.org>,
        Aditya Garg <gargaditya08@...e.com>,
        Aun-Ali Zaidi <admin@...eit.net>,
        Kerem Karabay <kekrby@...il.com>
Subject: Re: [PATCH v2 5/5] apple-gmux: add debugfs interface

Hi,

On 2/16/23 13:23, Orlando Chamberlain wrote:
> Allow reading and writing gmux ports from userspace.
> 
> For example:
> 
> echo 4 > /sys/kernel/debug/apple_gmux/selected_port
> cat /sys/kernel/debug/apple_gmux/selected_port_data | xxd -p
> 
> Will show the gmux version information (00000005 in this case)
> 
> Signed-off-by: Orlando Chamberlain <orlandoch.dev@...il.com>
> ---
> v1->v2: Use debugfs instead of sysfs.
>  drivers/platform/x86/apple-gmux.c | 88 +++++++++++++++++++++++++++++++
>  1 file changed, 88 insertions(+)
> 
> diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
> index 5bac6dcfada0..e8a35d98b113 100644
> --- a/drivers/platform/x86/apple-gmux.c
> +++ b/drivers/platform/x86/apple-gmux.c
> @@ -22,6 +22,7 @@
>  #include <linux/delay.h>
>  #include <linux/pci.h>
>  #include <linux/vga_switcheroo.h>
> +#include <linux/debugfs.h>
>  #include <asm/io.h>
>  
>  /**
> @@ -66,6 +67,10 @@ struct apple_gmux_data {
>  	enum vga_switcheroo_client_id switch_state_external;
>  	enum vga_switcheroo_state power_state;
>  	struct completion powerchange_done;
> +
> +	/* debugfs data */
> +	u8 selected_port;
> +	struct dentry *debug_dentry;
>  };
>  
>  static struct apple_gmux_data *apple_gmux_data;
> @@ -674,6 +679,87 @@ static void gmux_notify_handler(acpi_handle device, u32 value, void *context)
>  		complete(&gmux_data->powerchange_done);
>  }
>  
> +/**
> + * DOC: Debugfs Interface
> + *
> + * gmux ports can be accessed from userspace as a debugfs interface. For example:
> + *
> + * # echo 4 > /sys/kernel/debug/apple_gmux/selected_port
> + * # cat /sys/kernel/debug/apple_gmux/selected_port_data | xxd -p
> + * 00000005
> + *
> + * Reads 4 bytes from port 4 (GMUX_PORT_VERSION_MAJOR).
> + *
> + * 1 and 4 byte writes are also allowed.
> + */
> +
> +static ssize_t gmux_selected_port_data_write(struct file *file,
> +		const char __user *userbuf, size_t count, loff_t *ppos)
> +{
> +	struct apple_gmux_data *gmux_data = file->private_data;
> +	int ret;
> +
> +	if (*ppos)
> +		return -EINVAL;
> +
> +	if (count == 1) {
> +		u8 data;
> +
> +		ret = copy_from_user(&data, userbuf, 1);
> +		if (ret)
> +			return ret;
> +		gmux_write8(gmux_data, gmux_data->selected_port, data);
> +	} else if (count == 4) {
> +		u32 data;
> +
> +		ret = copy_from_user(&data, userbuf, 4);
> +		if (ret)
> +			return ret;
> +		gmux_write32(gmux_data, gmux_data->selected_port, data);
> +	} else
> +		return -EINVAL;
> +
> +	return count;
> +}
> +
> +static ssize_t gmux_selected_port_data_read(struct file *file,
> +		char __user *userbuf, size_t count, loff_t *ppos)
> +{
> +	struct apple_gmux_data *gmux_data = file->private_data;
> +	u32 data;
> +
> +	data = gmux_read32(gmux_data, gmux_data->selected_port);
> +
> +	return simple_read_from_buffer(userbuf, count, ppos, &data, sizeof(data));
> +}
> +
> +static const struct file_operations gmux_port_data_ops = {
> +	.open = simple_open,
> +	.write = gmux_selected_port_data_write,
> +	.read = gmux_selected_port_data_read
> +};
> +
> +static void gmux_init_debugfs(struct apple_gmux_data *gmux_data)
> +{
> +	struct dentry *debug_dentry;
> +
> +	debug_dentry = debugfs_create_dir(KBUILD_MODNAME, NULL);
> +
> +	if (IS_ERR(debug_dentry))
> +		return;

This error check is not necessary here. The debugfs_create_*
and debugfs_remove_recursive() functions will happily take
the ERR_PTR value and ignore it.

This is what I tried to say when I said that no error handling
is necessary with debugfs (by design).

Regards,

Hans


> +
> +	gmux_data->debug_dentry = debug_dentry;
> +
> +	debugfs_create_u8("selected_port", 0644, debug_dentry, &gmux_data->selected_port);
> +	debugfs_create_file("selected_port_data", 0644, debug_dentry,
> +			gmux_data, &gmux_port_data_ops);
> +}
> +
> +static void gmux_fini_debugfs(struct apple_gmux_data *gmux_data)
> +{
> +	debugfs_remove_recursive(gmux_data->debug_dentry);
> +}
> +
>  static int gmux_suspend(struct device *dev)
>  {
>  	struct pnp_dev *pnp = to_pnp_dev(dev);
> @@ -874,6 +960,7 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
>  		goto err_register_handler;
>  	}
>  
> +	gmux_init_debugfs(gmux_data);
>  	return 0;
>  
>  err_register_handler:
> @@ -905,6 +992,7 @@ static void gmux_remove(struct pnp_dev *pnp)
>  {
>  	struct apple_gmux_data *gmux_data = pnp_get_drvdata(pnp);
>  
> +	gmux_fini_debugfs(gmux_data);
>  	vga_switcheroo_unregister_handler();
>  	gmux_disable_interrupts(gmux_data);
>  	if (gmux_data->gpe >= 0) {