Re: [RFC PATCH 7/9] apple-gmux: add sysfs interface

[Orlando Chamberlain <orlandoch.dev@gmail.com>]

On Fri, 10 Feb 2023 21:23:15 +0100
Hans de Goede <hdegoede@redhat.com> wrote:

> Hi,
> 
> On 2/10/23 21:15, Hans de Goede wrote:
> > Hi,
> > 
> > On 2/10/23 05:48, Orlando Chamberlain wrote:  
> >> Allow reading gmux ports from userspace. When the unsafe module
> >> parameter allow_user_writes is true, writing 1 byte
> >> values is also allowed.
> >>
> >> For example:
> >>
> >> cd /sys/bus/acpi/devices/APP000B:00/physical_node/
> >> echo 4 > gmux_selected_port
> >> cat gmux_selected_port_data | xxd -p
> >>
> >> Will show the gmux version information (00000005 in this case)  
> > 
> > Please use debugfs for this and as part of the conversion
> > drop the #ifdef-s (debugfs has stubs for when not enabled)
> > and drop all the error checking of creating the files, debugfs
> > is deliberately designed to not have any error checking in
> > the setup / teardown code.
> > 
> > This also removes the need for the allow_user_writes parameter
> > replacing it with the new kernel lockdown mechanism. debugfs
> > will automatically block access to writable files when
> > the kernel is in lockdown mode.

I'll change it to use debugfs instead of sysfs in v2.

> > 
> > Regards,
> > 
> > Hans  
> 
> p.s.
> 
> I just realized I forgot my usual thank you for contributing
> to the kernel reply to the cover letter before diving into
> the review (oops).
> 
> So let me correct that: thank you very much for your work on this!

thank you for maintaining and reviewing!
> 
> Regards,
> 
> Hans
> 
> 
> 
> 
> 
> 
> >> Signed-off-by: Orlando Chamberlain <orlandoch.dev@gmail.com>
> >> ---
> >>  drivers/platform/x86/apple-gmux.c | 129
> >> ++++++++++++++++++++++++++++++ 1 file changed, 129 insertions(+)
> >>
> >> diff --git a/drivers/platform/x86/apple-gmux.c
> >> b/drivers/platform/x86/apple-gmux.c index
> >> c38d6ef0c15a..756059d48393 100644 ---
> >> a/drivers/platform/x86/apple-gmux.c +++
> >> b/drivers/platform/x86/apple-gmux.c @@ -66,6 +66,11 @@ struct
> >> apple_gmux_data { enum vga_switcheroo_client_id
> >> switch_state_external; enum vga_switcheroo_state power_state;
> >>  	struct completion powerchange_done;
> >> +
> >> +#ifdef CONFIG_SYSFS
> >> +	/* sysfs data */
> >> +	int selected_port;
> >> +#endif /* CONFIG_SYSFS */
> >>  };
> >>  
> >>  static struct apple_gmux_data *apple_gmux_data;
> >> @@ -651,6 +656,121 @@ static void gmux_notify_handler(acpi_handle
> >> device, u32 value, void *context)
> >> complete(&gmux_data->powerchange_done); }
> >>  
> >> +/**
> >> + * DOC: Sysfs Interface
> >> + *
> >> + * gmux ports can be read from userspace as a sysfs interface.
> >> For example:
> >> + *
> >> + * # echo 4 >
> >> /sys/bus/acpi/devices/APP000B:00/physical_node/gmux_selected_port
> >> + * # cat
> >> /sys/bus/acpi/devices/APP000B:00/physical_node/gmux_selected_port_data
> >> | xxd -p
> >> + * 00000005
> >> + *
> >> + * Reads 4 bytes from port 4 (GMUX_PORT_VERSION_MAJOR).
> >> + *
> >> + * Single byte writes are also supported, however this must be
> >> enabled with the
> >> + * unsafe allow_user_writes module parameter.
> >> + *
> >> + */
> >> +
> >> +#ifdef CONFIG_SYSFS
> >> +
> >> +static bool allow_user_writes;
> >> +module_param_unsafe(allow_user_writes, bool, 0);
> >> +MODULE_PARM_DESC(allow_user_writes, "Allow userspace to write to
> >> gmux ports (default: false) (bool)"); +
> >> +static ssize_t gmux_selected_port_store(struct device *dev,
> >> +		struct device_attribute *attr, const char
> >> *sysfsbuf, size_t count) +{
> >> +	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
> >> +	u8 port;
> >> +
> >> +	if (kstrtou8(sysfsbuf, 10, &port) < 0)
> >> +		return -EINVAL;
> >> +
> >> +	/* On pio gmux's, make sure the user doesn't access too
> >> high of a port. */
> >> +	if ((gmux_data->config == &apple_gmux_pio) &&
> >> +		port > (gmux_data->iolen - 4))
> >> +		return -EINVAL;
> >> +
> >> +	gmux_data->selected_port = port;
> >> +	return count;
> >> +}
> >> +
> >> +static ssize_t gmux_selected_port_show(struct device *dev,
> >> +		struct device_attribute *attr, char *sysfsbuf)
> >> +{
> >> +	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
> >> +
> >> +	return sysfs_emit(sysfsbuf, "%d\n",
> >> gmux_data->selected_port); +}
> >> +
> >> +DEVICE_ATTR_RW(gmux_selected_port);
> >> +
> >> +static ssize_t gmux_selected_port_data_store(struct device *dev,
> >> +		struct device_attribute *attr, const char
> >> *sysfsbuf, size_t count) +{
> >> +	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
> >> +
> >> +	if (count == 1)
> >> +		gmux_write8(gmux_data, gmux_data->selected_port,
> >> *sysfsbuf);
> >> +	else
> >> +		return -EINVAL;
> >> +
> >> +	return count;
> >> +}
> >> +
> >> +static ssize_t gmux_selected_port_data_show(struct device *dev,
> >> +		struct device_attribute *attr, char *sysfsbuf)
> >> +{
> >> +	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
> >> +	u32 data;
> >> +
> >> +	data = gmux_read32(gmux_data, gmux_data->selected_port);
> >> +	memcpy(sysfsbuf, &data, sizeof(data));
> >> +
> >> +	return sizeof(data);
> >> +}
> >> +
> >> +struct device_attribute dev_attr_gmux_selected_port_data_rw =
> >> __ATTR_RW(gmux_selected_port_data); +struct device_attribute
> >> dev_attr_gmux_selected_port_data_ro =
> >> __ATTR_RO(gmux_selected_port_data); + +static int
> >> gmux_init_sysfs(struct pnp_dev *pnp) +{
> >> +	int ret;
> >> +
> >> +	ret = device_create_file(&pnp->dev,
> >> &dev_attr_gmux_selected_port);
> >> +	if (ret)
> >> +		return ret;
> >> +	if (allow_user_writes)
> >> +		ret = device_create_file(&pnp->dev,
> >> &dev_attr_gmux_selected_port_data_rw);
> >> +	else
> >> +		ret = device_create_file(&pnp->dev,
> >> &dev_attr_gmux_selected_port_data_ro);
> >> +	if (ret)
> >> +		device_remove_file(&pnp->dev,
> >> &dev_attr_gmux_selected_port);
> >> +	return ret;
> >> +}
> >> +
> >> +static void gmux_fini_sysfs(struct pnp_dev *pnp)
> >> +{
> >> +	device_remove_file(&pnp->dev,
> >> &dev_attr_gmux_selected_port);
> >> +	if (allow_user_writes)
> >> +		device_remove_file(&pnp->dev,
> >> &dev_attr_gmux_selected_port_data_rw);
> >> +	else
> >> +		device_remove_file(&pnp->dev,
> >> &dev_attr_gmux_selected_port_data_ro); +}
> >> +
> >> +#else
> >> +
> >> +static int gmux_init_sysfs(struct pnp_dev *pnp)
> >> +{
> >> +	return 0;
> >> +}
> >> +static void gmux_fini_sysfs(struct pnp_dev *pnp)
> >> +{
> >> +}
> >> +
> >> +#endif /* CONFIG_SYSFS */
> >> +
> >>  static int gmux_suspend(struct device *dev)
> >>  {
> >>  	struct pnp_dev *pnp = to_pnp_dev(dev);
> >> @@ -846,8 +966,16 @@ static int gmux_probe(struct pnp_dev *pnp,
> >> const struct pnp_device_id *id) goto err_register_handler;
> >>  	}
> >>  
> >> +	ret = gmux_init_sysfs(pnp);
> >> +	if (ret) {
> >> +		pr_err("Failed to register gmux sysfs entries\n");
> >> +		goto err_sysfs;
> >> +	}
> >> +
> >>  	return 0;
> >>  
> >> +err_sysfs:
> >> +	vga_switcheroo_unregister_handler();
> >>  err_register_handler:
> >>  	gmux_disable_interrupts(gmux_data);
> >>  	apple_gmux_data = NULL;
> >> @@ -877,6 +1005,7 @@ static void gmux_remove(struct pnp_dev *pnp)
> >>  {
> >>  	struct apple_gmux_data *gmux_data = pnp_get_drvdata(pnp);
> >>  
> >> +	gmux_fini_sysfs(pnp);
> >>  	vga_switcheroo_unregister_handler();
> >>  	gmux_disable_interrupts(gmux_data);
> >>  	if (gmux_data->gpe >= 0) {  
> >   
>