Re: [PATCH v10 3/4] PCI/DOE: Expose the DOE features via sysfs

[Alistair Francis]

On Thu, May 23, 2024 at 9:24 PM Jonathan Cameron
<Jonathan.Cameron@xxxxxxxxxx> wrote:
>
> On Wed, 22 May 2024 20:11:41 +1000
> Alistair Francis <alistair23@xxxxxxxxx> wrote:
>
> > The PCIe 6 specification added support for the Data Object
> > Exchange (DOE).
> > When DOE is supported the DOE Discovery Feature must be implemented per
> > PCIe r6.1 sec 6.30.1.1. The protocol allows a requester to obtain
> > information about the other DOE features supported by the device.
> >
> > The kernel is already querying the DOE features supported and cacheing
> > the values. Expose the values in sysfs to allow user space to
> > determine which DOE features are supported by the PCIe device.
> >
> > By exposing the information to userspace tools like lspci can relay the
> > information to users. By listing all of the supported features we can
> > allow userspace to parse the list, which might include
> > vendor specific features as well as yet to be supported features.
> >
> > As the DOE Discovery feature must always be supported we treat it as a
> > special named attribute case. This allows the usual PCI attribute_group
> > handling to correctly create the doe_features directory when registering
> > pci_doe_sysfs_group (otherwise it doesn't and sysfs_add_file_to_group()
> > will seg fault).
> >
> > After this patch is supported you can see something like this when
> > attaching a DOE device
> >
> > $ ls /sys/devices/pci0000:00/0000:00:02.0//doe*
> > 0001:01        0001:02        doe_discovery
> >
> > Signed-off-by: Alistair Francis <alistair.francis@xxxxxxx>
>
> What happens if multiple DOE which support the same protocol?
> (IIRC that's allowed).  You probably need to paper over repeat
> sysfs attributes and make sure they don't get double freed etc.

Fair point. I changed pci_doe_sysfs_feature_populate() to not fall
over if the entry already exists, we just skip adding it.

pci_doe_sysfs_feature_remove() should already handle double entries
with the attrs[i].show check.

>
> Otherwise some minor things inline.
>
> Jonathan
>
>
> > ---
> > v10:
> >  - Rebase to use DEFINE_SYSFS_GROUP_VISIBLE and remove
> >    special setup function
> > v9:
> >  - Add a teardown function
> >  - Rename functions to be clearer
> >  - Tidy up the commit message
> >  - Remove #ifdef from header
> > v8:
> >  - Inlucde an example in the docs
> >  - Fixup removing a file that wasn't added
> >  - Remove a blank line
> > v7:
> >  - Fixup the #ifdefs to keep the test robot happy
> > v6:
> >  - Use "feature" instead of protocol
> >  - Don't use any devm_* functions
> >  - Add two more patches to the series
> > v5:
> >  - Return the file name as the file contents
> >  - Code cleanups and simplifications
> > v4:
> >  - Fixup typos in the documentation
> >  - Make it clear that the file names contain the information
> >  - Small code cleanups
> >  - Remove most #ifdefs
> >  - Remove extra NULL assignment
> > v3:
> >  - Expose each DOE feature as a separate file
> > v2:
> >  - Add documentation
> >  - Code cleanups
> >
> >  Documentation/ABI/testing/sysfs-bus-pci |  28 ++++
> >  drivers/pci/doe.c                       | 175 ++++++++++++++++++++++++
> >  drivers/pci/pci-sysfs.c                 |  13 ++
> >  drivers/pci/pci.h                       |  10 ++
> >  4 files changed, 226 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> > index ecf47559f495..65a3238ab701 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-pci
> > +++ b/Documentation/ABI/testing/sysfs-bus-pci
> > @@ -500,3 +500,31 @@ Description:
> >               console drivers from the device.  Raw users of pci-sysfs
> >               resourceN attributes must be terminated prior to resizing.
> >               Success of the resizing operation is not guaranteed.
> > +
> > +What:                /sys/bus/pci/devices/.../doe_features
> > +Date:                May 2024
> > +Contact:     Linux PCI developers <linux-pci@xxxxxxxxxxxxxxx>
> > +Description:
> > +             This directory contains a list of the supported
> > +             Data Object Exchange (DOE) features. The features are
> > +             the file name. The contents of each file is the raw vendor id and
> > +             data object feature values.
> > +
> > +             The value comes from the device and specifies the vendor and
> > +             data object type supported. The lower (RHS of the colon) is
> > +             the data object type in hex. The upper (LHS of the colon)
> > +             is the vendor ID.
> > +
> > +             As all DOE devices must support the DOE discovery protocol, if
> > +             DOE is supported you will at least see the doe_discovery file, with
> > +             this contents
> > +
> > +             # cat doe_features/doe_discovery
> > +             0001:00
> > +
> > +             If the device supports other protocols you will see other files
> > +             as well. For example is CMA/SPDM and secure CMA/SPDM are supported
> > +             the doe_features directory will look like this
> > +
> > +             # ls doe_features
> > +             0001:01        0001:02        doe_discovery
> > diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> > index defc4be81bd4..7a20a257df5a 100644
> > --- a/drivers/pci/doe.c
> > +++ b/drivers/pci/doe.c
> > @@ -47,6 +47,7 @@
> >   * @wq: Wait queue for work item
> >   * @work_queue: Queue of pci_doe_work items
> >   * @flags: Bit array of PCI_DOE_FLAG_* flags
> > + * @sysfs_attrs: Array of sysfs device attributes
> >   */
> >  struct pci_doe_mb {
> >       struct pci_dev *pdev;
> > @@ -56,6 +57,10 @@ struct pci_doe_mb {
> >       wait_queue_head_t wq;
> >       struct workqueue_struct *work_queue;
> >       unsigned long flags;
> > +
> > +#ifdef CONFIG_SYSFS
> > +     struct device_attribute *sysfs_attrs;
> > +#endif
> >  };
> >
> >  struct pci_doe_feature {
> > @@ -92,6 +97,176 @@ struct pci_doe_task {
> >       struct pci_doe_mb *doe_mb;
> >  };
> >
> > +#ifdef CONFIG_SYSFS
> > +static ssize_t doe_discovery_show(struct device *dev,
> > +                               struct device_attribute *attr,
> > +                               char *buf)
> > +{
> > +     return sysfs_emit(buf, "0001:00\n");
> > +}
> > +DEVICE_ATTR_RO(doe_discovery);
> > +
> > +static struct attribute *pci_doe_sysfs_feature_attrs[] = {
> > +     &dev_attr_doe_discovery.attr,
> > +     NULL,
>
> No comma needed on the null terminator as we'll never add anything after
> it.
>
> > +};
> > +
> > +static umode_t pci_doe_sysfs_attr_visible(struct kobject *kobj,
> > +                                       struct attribute *a, int n)
> > +{
> > +     struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
> > +     struct pci_doe_mb *doe_mb;
> > +     unsigned long index, j;
> > +     unsigned long vid, type;
> > +     void *entry;
> > +
> > +     xa_for_each(&pdev->doe_mbs, index, doe_mb) {
> > +             xa_for_each(&doe_mb->feats, j, entry) {
> > +                     vid = xa_to_value(entry) >> 8;
> > +                     type = xa_to_value(entry) & 0xFF;
> > +
> > +                     if (vid == 0x01 && type == 0x00) {
> > +                             /* This is the DOE discovery protocol
> local comment syntax is the
>                                 /*
>                                  * This is the
> form so stick to that.
>
>
> Shouldn't this also return a->mode for any case where the particular attribute
> matches?  I guess is_visible() isn't called for late registered sysfs attributes
> though I think it probably should be!

The is_visible is only called for the original doe_features attribute,
I will update the names of the functions to make this clear.

>
> > +                              * Every DOE instance must support this, so we
> > +                              * give it a useful name.
> > +                              */
> > +                             return a->mode;
> > +                     }
> > +             }
> > +     }
> > +
> > +     return 0;
> > +}
> > +
> > +static bool pci_doe_sysfs_group_visible(struct kobject *kobj)
> > +{
> > +     struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
> > +     struct pci_doe_mb *doe_mb;
> > +     unsigned long index, j;
> > +     void *entry;
> > +
> > +     xa_for_each(&pdev->doe_mbs, index, doe_mb) {
> > +             xa_for_each(&doe_mb->feats, j, entry)
> Is this simpler as
>                 if (!xa_empty(&doe_mb->feats))
>                         return true;

Fine with me

>
> > +                     return true;
> > +     }
> > +
> > +     return false;
> > +}
> > +DEFINE_SYSFS_GROUP_VISIBLE(pci_doe_sysfs)
> > +
> > +const struct attribute_group pci_doe_sysfs_group = {
> > +     .name       = "doe_features",
> > +     .attrs      = pci_doe_sysfs_feature_attrs,
> > +     .is_visible = SYSFS_GROUP_VISIBLE(pci_doe_sysfs),
> > +};
> > +
> > +static ssize_t pci_doe_sysfs_feature_show(struct device *dev,
> > +                                       struct device_attribute *attr,
> > +                                       char *buf)
> > +{
> > +     return sysfs_emit(buf, "%s\n", attr->attr.name);
> > +}
> > +
> > +static void pci_doe_sysfs_feature_remove(struct pci_dev *pdev,
> > +                                      struct pci_doe_mb *doe_mb)
> > +{
> > +     struct device_attribute *attrs = doe_mb->sysfs_attrs;
> > +     struct device *dev = &pdev->dev;
> > +     unsigned long i;
> > +     void *entry;
> > +
> > +     if (!attrs)
> > +             return;
> > +
> > +     doe_mb->sysfs_attrs = NULL;
> > +     xa_for_each(&doe_mb->feats, i, entry) {
>
> I'm not particularly keen on using an index over the xa
> just to get the number of elements for the loop limit.
> Maybe just store that when you allocate attrs?

Is that really any better? Then we have another value to keep track
of. Plus this gets trickier if we skip a duplicate entry.

>
> > +             if (attrs[i].show)
> > +                     sysfs_remove_file_from_group(&dev->kobj, &attrs[i].attr,
> > +                                                  pci_doe_sysfs_group.name);
> > +             kfree(attrs[i].attr.name);
> > +     }
> > +     kfree(attrs);
> > +}
> > +
> > +static int pci_doe_sysfs_feature_populate(struct pci_dev *pdev,
> > +                                       struct pci_doe_mb *doe_mb)
> > +{
> > +     struct device *dev = &pdev->dev;
> > +     struct device_attribute *attrs;
> > +     unsigned long num_features = 0;
> > +     unsigned long vid, type;
> > +     unsigned long i;
> > +     void *entry;
> > +     int ret;
> > +
> > +     xa_for_each(&doe_mb->feats, i, entry)
> > +             num_features++;
> > +
> > +     attrs = kcalloc(num_features, sizeof(*attrs), GFP_KERNEL);
> > +     if (!attrs)
> > +             return -ENOMEM;
> > +
> > +     doe_mb->sysfs_attrs = attrs;
> > +     xa_for_each(&doe_mb->feats, i, entry) {
> > +             sysfs_attr_init(&attrs[i].attr);
> > +             vid = xa_to_value(entry) >> 8;
> > +             type = xa_to_value(entry) & 0xFF;
> > +
> > +             if (vid == 0x01 && type == 0x00) {
> > +                     // DOE Discovery, manually displayed by `dev_attr_doe_discovery`
>
> /* */ syntax.
>
> > +                     continue;
> > +             }
> > +
> > +             attrs[i].attr.name = kasprintf(GFP_KERNEL,
> > +                                            "%04lx:%02lx", vid, type);
> > +             if (!attrs[i].attr.name) {
> > +                     ret = -ENOMEM;
> > +                     goto fail;
> > +             }
> > +
> > +             attrs[i].attr.mode = 0444;
> > +             attrs[i].show = pci_doe_sysfs_feature_show;
> > +
> > +             ret = sysfs_add_file_to_group(&dev->kobj, &attrs[i].attr,
> > +                                           pci_doe_sysfs_group.name);
> > +             if (ret) {
> > +                     attrs[i].show = NULL;
> > +                     goto fail;
>
> Repeated DOE 'features' on different DOE instances may cause this to fail.

We just skip that case then

Alistair

>
>
> > +             }
> > +     }
> > +
> > +     return 0;
> > +
> > +fail:
> > +     pci_doe_sysfs_feature_remove(pdev, doe_mb);
> > +     return ret;
> > +}
>
> >  static int pci_doe_wait(struct pci_doe_mb *doe_mb, unsigned long timeout)
> >  {
> >       if (wait_event_timeout(doe_mb->wq,
> > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > index 40cfa716392f..b5db191cb29f 100644
> > --- a/drivers/pci/pci-sysfs.c
> > +++ b/drivers/pci/pci-sysfs.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/kernel.h>
> >  #include <linux/sched.h>
> >  #include <linux/pci.h>
> > +#include <linux/pci-doe.h>
> >  #include <linux/stat.h>
> >  #include <linux/export.h>
> >  #include <linux/topology.h>
> > @@ -1143,6 +1144,9 @@ static void pci_remove_resource_files(struct pci_dev *pdev)
> >  {
> >       int i;
> >
> > +     if (IS_ENABLED(CONFIG_PCI_DOE))
> > +             pci_doe_sysfs_teardown(pdev);
> > +
> >       for (i = 0; i < PCI_STD_NUM_BARS; i++) {
> >               struct bin_attribute *res_attr;
> >
> > @@ -1227,6 +1231,12 @@ static int pci_create_resource_files(struct pci_dev *pdev)
> >       int i;
> >       int retval;
> >
> > +     if (IS_ENABLED(CONFIG_PCI_DOE)) {
> > +             retval = pci_doe_sysfs_init(pdev);
> > +             if (retval)
> > +                     return retval;
> > +     }
> > +
> >       /* Expose the PCI resources from this device as files */
> >       for (i = 0; i < PCI_STD_NUM_BARS; i++) {
> >
> > @@ -1661,6 +1671,9 @@ const struct attribute_group *pci_dev_attr_groups[] = {
> >  #endif
> >  #ifdef CONFIG_PCIEASPM
> >       &aspm_ctrl_attr_group,
> > +#endif
> > +#ifdef CONFIG_PCI_DOE
> > +     &pci_doe_sysfs_group,
> >  #endif
> >       NULL,
> >  };
>
>