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

[Hans de Goede]

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.
> 
> 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!

Regards,

Hans






>> Signed-off-by: Orlando Chamberlain <orlandoch.dev@xxxxxxxxx>
>> ---
>>  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) {
>