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

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Message-ID: <20230217102816.728dc1c3@redecorated-mbp>
Date:   Fri, 17 Feb 2023 10:28:16 +1100
From:   Orlando Chamberlain <orlandoch.dev@...il.com>
To:     Hans de Goede <hdegoede@...hat.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

On Thu, 16 Feb 2023 14:20:27 +0100
Hans de Goede <hdegoede@...hat.com> wrote:

> 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).
> 

I see, I'll simplify it to not check that in v3.

> 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) {  
>