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SubjectRe: [PATCH v3] driver core: Add sysfs support for physical location of a device
Hi Greg,

Thank you for the review.

I have a few questions on your comments.


On Sun, Mar 6, 2022 at 6:04 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Sat, Mar 05, 2022 at 12:42:58AM +0000, Won Chung wrote:
> > When ACPI table includes _PLD fields for a device, create a new
> > directory (physical_location) in sysfs to share _PLD fields.
> >
> > Currently without PLD information, when there are multiple of same
> > devices, it is hard to distinguish which device corresponds to which
> > physical device at which location. For example, when there are two Type
> > C connectors, it is hard to find out which connector corresponds to the
> > Type C port on the left panel versus the Type C port on the right panel.
> > With PLD information provided, we can determine which specific device at
> > which location is doing what.
> >
> > _PLD output includes much more fields, but only generic fields are added
> > and exposed to sysfs, so that non-ACPI devices can also support it in
> > the future. The minimal generic fields needed for locating a device are
> > the following.
> > - panel
> > - vertical_position
> > - horizontal_position
> > - dock
> > - lid
> >
> > Signed-off-by: Won Chung <wonchung@google.com>
> > ---
> >
> > Changes from v2
> > - Use sysfs_emit to create files.
> > - Correct mix of spaces and tabs.
> >
> > Changes from v1
> > - Correct directory names in Documentation.
> > - Clarify namings in core.c
> >
> > .../testing/sysfs-devices-physical_location | 42 ++++++
> > drivers/base/core.c | 139 ++++++++++++++++++
> > include/linux/device.h | 73 +++++++++
> > 3 files changed, 254 insertions(+)
> > create mode 100644 Documentation/ABI/testing/sysfs-devices-physical_location
> >
> > diff --git a/Documentation/ABI/testing/sysfs-devices-physical_location b/Documentation/ABI/testing/sysfs-devices-physical_location
> > new file mode 100644
> > index 000000000000..202324b87083
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-devices-physical_location
> > @@ -0,0 +1,42 @@
> > +What: /sys/devices/.../physical_location
> > +Date: March 2022
> > +Contact: Won Chung <wonchung@google.com>
> > +Description:
> > + This directory contains information on physical location of
> > + the device connection point with respect to the system's
> > + housing.
> > +
> > +What: /sys/devices/.../physical_location/panel
> > +Date: March 2022
> > +Contact: Won Chung <wonchung@google.com>
> > +Description:
> > + Describes which panel surface of the system’s housing the
> > + device connection point resides on.
> > +
> > +What: /sys/devices/.../physical_location/vertical_position
> > +Date: March 2022
> > +Contact: Won Chung <wonchung@google.com>
> > +Description:
> > + Describes vertical position of the device connection point on
> > + the panel surface.
> > +
> > +What: /sys/devices/.../physical_location/horizontal_position
> > +Date: March 2022
> > +Contact: Won Chung <wonchung@google.com>
> > +Description:
> > + Describes horizontal position of the device connection point on
> > + the panel surface.
> > +
> > +What: /sys/devices/.../physical_location/dock
> > +Date: March 2022
> > +Contact: Won Chung <wonchung@google.com>
> > +Description:
> > + "Yes" if the device connection point resides in a docking
> > + station or a port replicator. "No" otherwise.
> > +
> > +What: /sys/devices/.../physical_location/lid
> > +Date: March 2022
> > +Contact: Won Chung <wonchung@google.com>
> > +Description:
> > + "Yes" if the device connection point resides on the lid of
> > + laptop system. "No" otherwise.
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 7bb957b11861..9cfa71ad21f3 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -2466,6 +2466,136 @@ static ssize_t removable_show(struct device *dev, struct device_attribute *attr,
> > }
> > static DEVICE_ATTR_RO(removable);
> >
> > +static int dev_add_physical_location(struct device *dev)
> > +{
> > +#if defined(CONFIG_ACPI)
> > + struct acpi_pld_info *pld;
> > + acpi_status status;
> > +
> > + if (!has_acpi_companion(dev))
> > + return 0;
> > +
> > + status = acpi_get_physical_device_location(ACPI_HANDLE(dev), &pld);
> > + if (ACPI_FAILURE(status) || !pld)
> > + return 0;
> > +
> > + dev->location = (struct device_location) {
> > + .panel = pld->panel,
> > + .vertical_position = pld->vertical_position,
> > + .horizontal_position = pld->horizontal_position,
> > + .dock = pld->dock,
> > + .lid = pld->lid,
> > + };
>
> Is this a memcpy()? Ick, that's odd.
>
> > +
> > + return 1;
>
> Kernel functions do not return "1" as success. Or as an error.
> Positive numbers are ONLY for when to return the number of bytes
> consumed/written or the like.
>
> > +#else
>
> I have asked multiple times to not put #ifdef in .c files. I can't take
> this patch for that fact alone (also big hint, if acpi is not enabled,
> loads of these functions and the structure itself should not be present
> at all...)
>
>
>
>
>
> > + return 0;
> > +#endif
> > +}
> > +
> > +static ssize_t panel_show(struct device *dev, struct device_attribute *attr,
> > + char *buf)
> > +{
> > + const char *panel;
> > +
> > + switch (dev->location.panel) {
> > + case DEVICE_PANEL_TOP:
> > + panel = "top";
> > + break;
> > + case DEVICE_PANEL_BOTTOM:
> > + panel = "bottom";
> > + break;
> > + case DEVICE_PANEL_LEFT:
> > + panel = "left";
> > + break;
> > + case DEVICE_PANEL_RIGHT:
> > + panel = "right";
> > + break;
> > + case DEVICE_PANEL_FRONT:
> > + panel = "front";
> > + break;
> > + case DEVICE_PANEL_BACK:
> > + panel = "back";
> > + break;
> > + default:
> > + panel = "unknown";
> > + }
> > + return sysfs_emit(buf, "%s\n", panel);
> > +}
> > +static DEVICE_ATTR_RO(panel);
> > +
> > +static ssize_t vertical_position_show(struct device *dev,
> > + struct device_attribute *attr, char *buf)
> > +{
> > + const char *vertical_position;
> > +
> > + switch (dev->location.vertical_position) {
> > + case DEVICE_VERT_POS_UPPER:
> > + vertical_position = "upper";
> > + break;
> > + case DEVICE_VERT_POS_CENTER:
> > + vertical_position = "center";
> > + break;
> > + case DEVICE_VERT_POS_LOWER:
> > + vertical_position = "lower";
> > + break;
> > + default:
> > + vertical_position = "unknown";
> > + }
> > + return sysfs_emit(buf, "%s\n", vertical_position);
> > +}
> > +static DEVICE_ATTR_RO(vertical_position);
> > +
> > +static ssize_t horizontal_position_show(struct device *dev,
> > + struct device_attribute *attr, char *buf)
> > +{
> > + const char *horizontal_position;
> > +
> > + switch (dev->location.horizontal_position) {
> > + case DEVICE_HORI_POS_LEFT:
> > + horizontal_position = "left";
> > + break;
> > + case DEVICE_HORI_POS_CENTER:
> > + horizontal_position = "center";
> > + break;
> > + case DEVICE_HORI_POS_RIGHT:
> > + horizontal_position = "right";
> > + break;
> > + default:
> > + horizontal_position = "unknown";
> > + }
> > + return sysfs_emit(buf, "%s\n", horizontal_position);
> > +}
> > +static DEVICE_ATTR_RO(horizontal_position);
> > +
> > +static ssize_t dock_show(struct device *dev, struct device_attribute *attr,
> > + char *buf)
>
> Did you run your patch through checkpatch.pl?
>
> Please do so.
>

I think I did run checkpatch.pl. I tried again but there is no issue
other than a warning that the maintainers list may need to be updated
due to a new file. Do you think there is a style issue here?

> > +{
> > + return sysfs_emit(buf, "%s\n", dev->location.dock ? "yes" : "no");
> > +}
> > +static DEVICE_ATTR_RO(dock);
> > +
> > +static ssize_t lid_show(struct device *dev, struct device_attribute *attr,
> > + char *buf)
> > +{
> > + return sysfs_emit(buf, "%s\n", dev->location.lid ? "yes" : "no");
> > +}
> > +static DEVICE_ATTR_RO(lid);
> > +
> > +static struct attribute *dev_attr_physical_location[] = {
> > + &dev_attr_panel.attr,
> > + &dev_attr_vertical_position.attr,
> > + &dev_attr_horizontal_position.attr,
> > + &dev_attr_dock.attr,
> > + &dev_attr_lid.attr,
> > + NULL,
> > +};
> > +
> > +static const struct attribute_group dev_attr_physical_location_group = {
> > + .name = "physical_location",
>
> I'm all for being verbose, but why not just "location"? What other type
> of location is there for a device?

For USB ports, there seems to be a "location" file for u32 value
representing ACPI PLD group token and group location.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/core/port.c#n20

Would you prefer renaming that "location" file to something else and
have this one as "location" directory? Or would "physical_location" be
okay?

>
> > + .attrs = dev_attr_physical_location,
> > +};
> > +
> > int device_add_groups(struct device *dev, const struct attribute_group **groups)
> > {
> > return sysfs_create_groups(&dev->kobj, groups);
> > @@ -2649,8 +2779,17 @@ static int device_add_attrs(struct device *dev)
> > goto err_remove_dev_waiting_for_supplier;
> > }
> >
> > + if (dev_add_physical_location(dev)) {
> > + error = device_add_group(dev,
> > + &dev_attr_physical_location_group);
> > + if (error)
> > + goto err_remove_dev_physical_location;
> > + }
> > +
> > return 0;
> >
> > + err_remove_dev_physical_location:
> > + device_remove_group(dev, &dev_attr_physical_location_group);
> > err_remove_dev_waiting_for_supplier:
> > device_remove_file(dev, &dev_attr_waiting_for_supplier);
> > err_remove_dev_online:
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 93459724dcde..424be9cb735e 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -386,6 +386,75 @@ struct dev_msi_info {
> > #endif
> > };
> >
> > +/**
> > + * enum device_location_panel - Describes which panel surface of the system's
> > + * housing the device connection point resides on.
> > + * @DEVICE_PANEL_TOP: Device connection point is on the top panel.
> > + * @DEVICE_PANEL_BOTTOM: Device connection point is on the bottom panel.
> > + * @DEVICE_PANEL_LEFT: Device connection point is on the left panel.
> > + * @DEVICE_PANEL_RIGHT: Device connection point is on the right panel.
> > + * @DEVICE_PANEL_FRONT: Device connection point is on the front panel.
> > + * @DEVICE_PANEL_BACK: Device connection point is on the back panel.
> > + * @DEVICE_PANEL_UNKNOWN: The panel with device connection point is unknown.
> > + */
> > +enum device_location_panel {
> > + DEVICE_PANEL_TOP,
> > + DEVICE_PANEL_BOTTOM,
> > + DEVICE_PANEL_LEFT,
> > + DEVICE_PANEL_RIGHT,
> > + DEVICE_PANEL_FRONT,
> > + DEVICE_PANEL_BACK,
> > + DEVICE_PANEL_UNKNOWN,
> > +};
> > +
> > +/**
> > + * enum device_location_vertical_position - Describes vertical position of the
> > + * device connection point on the panel surface.
> > + * @DEVICE_VERT_POS_UPPER: Device connection point is at upper part of panel.
> > + * @DEVICE_VERT_POS_CENTER: Device connection point is at center part of panel.
> > + * @DEVICE_VERT_POS_LOWER: Device connection point is at lower part of panel.
> > + */
> > +enum device_location_vertical_position {
> > + DEVICE_VERT_POS_UPPER,
> > + DEVICE_VERT_POS_CENTER,
> > + DEVICE_VERT_POS_LOWER,
> > +};
> > +
> > +/**
> > + * enum device_location_horizontal_position - Describes horizontal position of
> > + * the device connection point on the panel surface.
> > + * @DEVICE_HORI_POS_LEFT: Device connection point is at left part of panel.
> > + * @DEVICE_HORI_POS_CENTER: Device connection point is at center part of panel.
> > + * @DEVICE_HORI_POS_RIGHT: Device connection point is at right part of panel.
> > + */
> > +enum device_location_horizontal_position {
> > + DEVICE_HORI_POS_LEFT,
> > + DEVICE_HORI_POS_CENTER,
> > + DEVICE_HORI_POS_RIGHT,
> > +};
>
> Why do these enum values need to be in device.h? Can they just live in
> drivers/base/ somewhere?
>

I was thinking that since these are information about device, they
could live in and be accessed through device.
Do you think this is not a good place for these enum and struct? Maybe
a new driver/base/location.h?

>
> > +
> > +/**
> > + * struct device_location - Device data related to physical location of the
> > + * device connection point.
> > + * @panel: Panel surface of the system's housing that the device connection
> > + * point resides on.
> > + * @vertical_position: Vertical position of the device connection point within
> > + * the panel.
> > + * @horizontal_position: Horizontal position of the device connection point
> > + * within the panel.
> > + * @dock: Set if the device connection point resides in a docking station or
> > + * port replicator.
> > + * @lid: Set if this device connection point resides on the lid of laptop
> > + * system.
> > + */
> > +struct device_location {
> > + enum device_location_panel panel;
> > + enum device_location_vertical_position vertical_position;
> > + enum device_location_horizontal_position horizontal_position;
> > + bool dock;
> > + bool lid;
>
> How badly did you just inflate all device structures in the kernel? Did
> you use 'pahole' to see if you added padding or not?
>

I did not use pahole. I tried it and it is giving 16 bytes for struct
device_location and 2 bytes of padding.
Would using device location* instead be better since that would be 8
bytes of inflation?

> > +};
> > +
> > /**
> > * struct device - The basic device structure
> > * @parent: The device's "parent" device, the device to which it is attached.
> > @@ -456,6 +525,8 @@ struct dev_msi_info {
> > * @removable: Whether the device can be removed from the system. This
> > * should be set by the subsystem / bus driver that discovered
> > * the device.
> > + * @location: Describes physical location of the device connection point in
> > + * the system housing.
> > *
> > * @offline_disabled: If set, the device is permanently online.
> > * @offline: Set after successful invocation of bus type's .offline().
> > @@ -569,6 +640,8 @@ struct device {
> >
> > enum device_removable removable;
> >
> > + struct device_location location;
>
> See, you just call it "location" here, not "physical_location", so why
> does userspace get a bigger name than the kernel does? :)
>
> thanks,
>
> greg k-h


Thank you,
Won

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