Re: [PATCH v2] Expose PCIe SSD Status LED Management DSM in sysfs

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Christoph, Dan, Greg (for "one value per file" question below)]

On Tue, Nov 10, 2020 at 09:37:35AM -0600, Stuart Hayes wrote:
> This patch will expose the PCIe SSD Status LED Management interface in
> sysfs for devices that have the relevant _DSM method, per the "_DSM
> additions for PCIe SSD Status LED Management" ECN to the PCI Firmware
> Specification revision 3.2.
> 
> The interface is exposed in two sysfs files, ssdleds_supported_states (RO)
> and ssdleds_current_state (RW).
> 
> Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
> ---
> 
> v2: made PCI_SSDLEDS dependent on PCI and ACPI
>     remove unused variable
>     warn if call to sysfs_create_group fails
>     include header file with function prototypes
>     change logical OR to bitwise
> 
> ---
>  Documentation/ABI/testing/sysfs-bus-pci |  14 ++
>  drivers/pci/Kconfig                     |   7 +
>  drivers/pci/Makefile                    |   1 +
>  drivers/pci/pci-ssdleds.c               | 194 ++++++++++++++++++++++++
>  drivers/pci/pci-sysfs.c                 |   1 +
>  drivers/pci/pci.h                       |  11 ++
>  6 files changed, 228 insertions(+)
>  create mode 100644 drivers/pci/pci-ssdleds.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 77ad9ec3c801..18ca73b764ac 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -366,3 +366,17 @@ Contact:	Heiner Kallweit <hkallweit1@gmail.com>
>  Description:	If ASPM is supported for an endpoint, these files can be
>  		used to disable or enable the individual power management
>  		states. Write y/1/on to enable, n/0/off to disable.
> +
> +What:		/sys/bus/pci/devices/.../ssdleds_supported_states
> +Date:		October 2020
> +Contact:	Stuart Hayes <stuart.w.hayes@gmail.com>
> +Description:	If the device supports the ACPI _DSM method to control the
> +		PCIe SSD LED states, ssdleds_supported_states (read only)
> +		will show the LED states that are supported by the _DSM.
> +
> +What:		/sys/bus/pci/devices/.../ssdleds_current_state
> +Date:		October 2020
> +Contact:	Stuart Hayes <stuart.w.hayes@gmail.com>
> +Description:	If the device supports the ACPI _DSM method to control the
> +		PCIe SSD LED states, ssdleds_current_state will show or set
> +		the current LED states that are active.
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 0c473d75e625..48049866145f 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -182,6 +182,13 @@ config PCI_LABEL
>  	def_bool y if (DMI || ACPI)
>  	select NLS
>  
> +config PCI_SSDLEDS
> +	def_bool y if (ACPI && PCI)
> +	depends on PCI && ACPI
> +	help
> +	  Enables userspace access to PCIe SSD LED management interface via
> +	  sysfs.
> +
>  config PCI_HYPERV
>  	tristate "Hyper-V PCI Frontend"
>  	depends on X86_64 && HYPERV && PCI_MSI && PCI_MSI_IRQ_DOMAIN && SYSFS
> diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
> index 522d2b974e91..75d3d5a3b1ed 100644
> --- a/drivers/pci/Makefile
> +++ b/drivers/pci/Makefile
> @@ -23,6 +23,7 @@ obj-$(CONFIG_PCI_ATS)		+= ats.o
>  obj-$(CONFIG_PCI_IOV)		+= iov.o
>  obj-$(CONFIG_PCI_BRIDGE_EMUL)	+= pci-bridge-emul.o
>  obj-$(CONFIG_PCI_LABEL)		+= pci-label.o
> +obj-$(CONFIG_PCI_SSDLEDS)	+= pci-ssdleds.o
>  obj-$(CONFIG_X86_INTEL_MID)	+= pci-mid.o
>  obj-$(CONFIG_PCI_SYSCALL)	+= syscall.o
>  obj-$(CONFIG_PCI_STUB)		+= pci-stub.o
> diff --git a/drivers/pci/pci-ssdleds.c b/drivers/pci/pci-ssdleds.c
> new file mode 100644
> index 000000000000..d35e4f3caa71
> --- /dev/null
> +++ b/drivers/pci/pci-ssdleds.c
> @@ -0,0 +1,194 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Provide userspace access to PCIe SSD Status LED Management
> + *
> + * The PCIe spec defines an ACPI _DSM method to allow PCIe SSD status LED

s/PCIe spec/PCI Firmware spec/

> + * management (see "_DSM additions for PCIe SSD Status LED Management" ECN,
> + * February 12, 2020). This code provides a sysfs interface to this _DSM.
> + *
> + * Copyright (C) 2020 Dell Inc.
> + *

Unnecessary blank line.

> + */
> +
> +#include <linux/sysfs.h>
> +#include <linux/pci.h>
> +#include <linux/device.h>
> +#include <linux/acpi.h>
> +#include "pci.h"
> +
> +const guid_t pci_ssdleds_dsm_guid =
> +	GUID_INIT(0x5d524d9d, 0xfff9, 0x4d4b,
> +		  0x8c, 0xb7, 0x74, 0x7e, 0xd5, 0x1e, 0x19, 0x4d);

Static?

> +#define SSDLEDS_GET_SUPPORTED_STATES_DSM	0x01
> +#define SSDLEDS_GET_STATE_DSM			0x02
> +#define SSDLEDS_SET_STATE_DSM			0x03
> +
> +struct pci_ssdleds_dsm_output {
> +	u16 status;
> +	u8 function_specific_err;
> +	u8 vendor_specific_err;
> +	u32 state;
> +};
> +
> +static int ssdleds_dsm_set(struct device *dev, const char *buf, u64 dsm_func)
> +{
> +	acpi_handle handle;
> +	union acpi_object *out_obj, arg3[2];
> +	struct pci_ssdleds_dsm_output *dsm_output;
> +	u32 val;
> +	int err;
> +
> +	handle = ACPI_HANDLE(dev);
> +	if (!handle)
> +		return -ENODEV;
> +
> +	err = kstrtou32(buf, 0, &val);
> +	if (err || val > U32_MAX)
> +		return -EINVAL;

"buf" is really a sysfs concept, not a _DSM concept, so I would
consider moving the kstrtou32() to the caller.

> +	arg3[0].type = ACPI_TYPE_PACKAGE;
> +	arg3[0].package.count = 1;
> +	arg3[0].package.elements = &arg3[1];
> +
> +	arg3[1].type = ACPI_TYPE_BUFFER;
> +	arg3[1].buffer.length = 4;
> +	arg3[1].buffer.pointer = (u8 *)&val;
> +
> +	out_obj = acpi_evaluate_dsm_typed(handle, &pci_ssdleds_dsm_guid, 0x1,
> +				      dsm_func, &arg3[0], ACPI_TYPE_BUFFER);
> +	if (!out_obj)
> +		return -EIO;
> +
> +	if (out_obj->buffer.length < 8) {
> +		ACPI_FREE(out_obj);
> +		return -EIO;
> +	}
> +
> +	dsm_output = (struct pci_ssdleds_dsm_output *)out_obj->buffer.pointer;
> +	/*
> +	 * Ignore function specific error bit 1 (some LED state bits weren't
> +	 * set), since write was done. User can read current state to see which
> +	 * bits were set.
> +	 */
> +	if (dsm_output->status != 0 &&
> +	    !(dsm_output->status == 4 && dsm_output->function_specific_err == 1)) {

It looks like this error check is specific to SSDLEDS_SET_STATE_DSM.

I know this function is currently only called for
SSDLEDS_SET_STATE_DSM, but I think you should either get rid of the
dsm_func argument and specify SSDLEDS_SET_STATE_DSM explicitly in
*this* function, or do this error check in the caller where you *know*
you're passing SSDLEDS_SET_STATE_DSM.

I guess the dsm_output you're checking only exists in this function,
so maybe the former?

> +		ACPI_FREE(out_obj);
> +		return -EIO;
> +	}
> +
> +	ACPI_FREE(out_obj);
> +
> +	return 0;
> +}
> +
> +static int ssdleds_dsm_get(struct device *dev, char *buf, u64 dsm_func)
> +{
> +	acpi_handle handle;
> +	union acpi_object *out_obj;
> +	struct pci_ssdleds_dsm_output *dsm_output;
> +
> +	handle = ACPI_HANDLE(dev);
> +	if (!handle)
> +		return -ENODEV;
> +
> +	out_obj = acpi_evaluate_dsm_typed(handle, &pci_ssdleds_dsm_guid, 0x1,
> +				      dsm_func, NULL, ACPI_TYPE_BUFFER);
> +	if (!out_obj)
> +		return -EIO;
> +
> +	if (out_obj->buffer.length < 8) {
> +		ACPI_FREE(out_obj);
> +		return -EIO;
> +	}
> +
> +	dsm_output = (struct pci_ssdleds_dsm_output *)out_obj->buffer.pointer;
> +	if (dsm_output->status != 0) {
> +		ACPI_FREE(out_obj);
> +		return -EIO;
> +	}
> +
> +	scnprintf(buf, PAGE_SIZE, "%#x\n", dsm_output->state);

Similarly, I would consider returning dsm_output->state and moving the
scnprintf() so the sysfs-specific stuff is in the caller.

It looks like you just expose the hex value that encodes things like:

  OK
  Locate
  Fail
  Rebuild
  ...

The hex value is sort of a pain to interpret, especially since the PCI
specs are not public.  Maybe consider decoding it?  If you did decode
it, that might be a way to reduce this to a single file instead of
having both "supported_states" and "current_state" -- the single file
could list all the supported states, with the current states
highlighted somehow.

Not sure if that would run afoul of the sysfs "one value per file"
rule.  CC'd Greg in case he wants to chime in.

> +	ACPI_FREE(out_obj);
> +
> +	return strlen(buf) > 0 ? strlen(buf) : -EIO;
> +}
> +
> +static bool device_has_dsm(struct device *dev)
> +{
> +	acpi_handle handle;
> +
> +	handle = ACPI_HANDLE(dev);
> +	if (!handle)
> +		return false;
> +
> +	return !!acpi_check_dsm(handle, &pci_ssdleds_dsm_guid, 0x1,
> +		       1 << SSDLEDS_GET_SUPPORTED_STATES_DSM |
> +		       1 << SSDLEDS_GET_STATE_DSM |
> +		       1 << SSDLEDS_SET_STATE_DSM);
> +}
> +
> +static ssize_t ssdleds_current_store(struct device *dev,
> +				struct device_attribute *attr,
> +				const char *buf, size_t count)
> +{
> +	int ret;
> +
> +	ret = ssdleds_dsm_set(dev, buf, SSDLEDS_SET_STATE_DSM);
> +	return (ret < 0) ? ret : count;
> +}
> +
> +static ssize_t ssdleds_current_show(struct device *dev,
> +			      struct device_attribute *attr, char *buf)
> +{
> +	return ssdleds_dsm_get(dev, buf, SSDLEDS_GET_STATE_DSM);
> +}
> +
> +static ssize_t ssdleds_supported_show(struct device *dev,
> +			      struct device_attribute *attr, char *buf)
> +{
> +	return ssdleds_dsm_get(dev, buf, SSDLEDS_GET_SUPPORTED_STATES_DSM);
> +}
> +
> +static umode_t ssdleds_attr_visible(struct kobject *kobj,
> +				    struct attribute *attr, int n)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	umode_t mode = attr->mode;
> +
> +	return device_has_dsm(dev) ? mode : 0;
> +}
> +
> +static struct device_attribute ssdleds_attr_current = {
> +	.attr = {.name = "ssdleds_current_state", .mode = 0644},
> +	.show = ssdleds_current_show,
> +	.store = ssdleds_current_store,
> +};

Can these use DEVICE_ATTR_RW() and friends?

> +static struct device_attribute ssdleds_attr_supported = {
> +	.attr = {.name = "ssdleds_supported_states", .mode = 0444},
> +	.show = ssdleds_supported_show,
> +};
> +
> +static struct attribute *ssdleds_attributes[] = {
> +	&ssdleds_attr_current.attr,
> +	&ssdleds_attr_supported.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group ssdleds_attr_group = {
> +	.attrs = ssdleds_attributes,
> +	.is_visible = ssdleds_attr_visible,
> +};
> +
> +void pci_create_ssdleds_files(struct pci_dev *pdev)
> +{
> +	if (sysfs_create_group(&pdev->dev.kobj, &ssdleds_attr_group))
> +		pci_warn(pdev, "Unable to create ssdleds attributes\n");
> +}
> +
> +void pci_remove_ssdleds_files(struct pci_dev *pdev)
> +{
> +	sysfs_remove_group(&pdev->dev.kobj, &ssdleds_attr_group);
> +}

I'm not a real sysfs expert, but I *think* that if you follow the
pattern in pci_dev_attr_groups[] in pci-sysfs.c, you won't need these
create/remove functions.

> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index d15c881e2e7e..820f32956971 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -1377,6 +1377,7 @@ int __must_check pci_create_sysfs_dev_files(struct pci_dev *pdev)
>  		goto err_rom_file;
>  
>  	pci_create_firmware_label_files(pdev);
> +	pci_create_ssdleds_files(pdev);
>  
>  	return 0;
>  
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index f86cae9aa1f4..8e6883a1b701 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -30,6 +30,17 @@ static inline void pci_remove_firmware_label_files(struct pci_dev *pdev)
>  void pci_create_firmware_label_files(struct pci_dev *pdev);
>  void pci_remove_firmware_label_files(struct pci_dev *pdev);
>  #endif
> +
> +#if !defined(CONFIG_PCI_SSDLEDS)
> +static inline void pci_create_ssdleds_files(struct pci_dev *pdev)
> +{ return; }
> +static inline void pci_remove_ssdleds_files(struct pci_dev *pdev)
> +{ return; }
> +#else
> +void pci_create_ssdleds_files(struct pci_dev *pdev);
> +void pci_remove_ssdleds_files(struct pci_dev *pdev);
> +#endif
> +
>  void pci_cleanup_rom(struct pci_dev *dev);
>  
>  enum pci_mmap_api {
> -- 
> 2.18.1
>