Re: [RFC PATCH 04/13] cxl: Add Get Supported Features command for kernel usage

Dave Jiang
2024-09-27T16:22:03Z

On 7/26/24 10:50 AM, Jonathan Cameron wrote:
> On Thu, 18 Jul 2024 14:32:22 -0700
> Dave Jiang <dave.jiang@intel.com> wrote:
>
>> CXL spec r3.1 8.2.9.6.1 Get Supported Features (Opcode 0500h)
>> The command retrieve the list of supported device-specific features
>> (identified by UUID) and general information about each Feature.
>>
>> The driver will retrieve the feature entries in order to make checks and
>> provide information for the Get Feature and Set Feature command. One of
>> the main piece of information retrieved are the effects a Set Feature
>> command would have for a particular feature.
>>
>> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
>
> Already a fairly well reviewed implementation of this in
>
> https://lore.kernel.org/linux-cxl/20240726160556.2079-5-shiju.jose@huawei.com/
>
> Though it wasn't focused on providing userspace access to it and doesn't handle
> large feature lists which would be eventually needed.
>
> I'd have preferred to see review on that rather than another version
> of the same functionality.
>
> Note the QEMU testing used for that set will be useable here too
> and is now upstream.
>
> A few comments inline.
>
> Jonathan
>
>
>> +int cxl_get_supported_features(struct cxl_mailbox *cxl_mbox)
>> +{
>> + int remain_feats, max_size, max_feats, start, rc;
>> + int feat_size = sizeof(struct cxl_feat_entry);
>> + struct cxl_mbox_get_sup_feats_out *mbox_out;
>> + struct cxl_mbox_get_sup_feats_in mbox_in;
>> + int hdr_size = sizeof(*mbox_out);
>> + struct cxl_mbox_cmd mbox_cmd;
>> + struct cxl_mem_command *cmd;
>> + void *ptr;
>> +
>> + /* Get supported features is optional, need to check */
>> + cmd = cxl_mem_find_command(CXL_MBOX_OP_GET_SUPPORTED_FEATURES);
>> + if (!cmd)
>> + return -EOPNOTSUPP;
>> + if (!test_bit(cmd->info.id, cxl_mbox->enabled_cmds))
>> + return -EOPNOTSUPP;
>> +
>> + rc = cxl_get_supported_features_count(cxl_mbox);
>> + if (rc)
>> + return rc;
>> +
>> + struct cxl_feat_entry *entries __free(kvfree) =
>> + kvmalloc(cxl_mbox->num_features * feat_size, GFP_KERNEL);
>> +
>> + if (!entries)
>> + return -ENOMEM;
>> +
>> + cxl_mbox->entries = no_free_ptr(entries);
>
> Hmm. Not srue I'd bother with __free(kvfree) for one line that doesn't
> do the free.
>
>> + rc = devm_add_action_or_reset(cxl_mbox->host, cxl_free_features,
>> + cxl_mbox->entries);
>> + if (rc)
>> + return rc;
>> +
>> + max_size = cxl_mbox->payload_size - hdr_size;
>> + /* max feat entries that can fit in mailbox max payload size */
>> + max_feats = max_size / feat_size;
>> + ptr = &cxl_mbox->entries[0];
>> +
>> + mbox_out = kvmalloc(cxl_mbox->payload_size, GFP_KERNEL);
> Freed?
>
>> + if (!mbox_out)
>> + return -ENOMEM;
>> +
>> + start = 0;
>> + remain_feats = cxl_mbox->num_features;
>> + do {
>> + int retrieved, alloc_size, copy_feats;
>> +
>> + if (remain_feats > max_feats) {
>> + alloc_size = sizeof(*mbox_out) + max_feats * feat_size;
>> + remain_feats = remain_feats - max_feats;
>> + copy_feats = max_feats;
>> + } else {
>> + alloc_size = sizeof(*mbox_out) + remain_feats * feat_size;
>> + copy_feats = remain_feats;
>> + remain_feats = 0;
>> + }
>> +
>> + memset(&mbox_in, 0, sizeof(mbox_in));
>> + mbox_in.count = alloc_size;
>> + mbox_in.start_idx = start;
>> + memset(mbox_out, 0, alloc_size);
>> + mbox_cmd = (struct cxl_mbox_cmd) {
>> + .opcode = CXL_MBOX_OP_GET_SUPPORTED_FEATURES,
>> + .size_in = sizeof(mbox_in),
>> + .payload_in = &mbox_in,
>> + .size_out = alloc_size,
>> + .payload_out = mbox_out,
>> + .min_out = hdr_size,
>> + };
>> + rc = cxl_internal_send_cmd(cxl_mbox, &mbox_cmd);
>> + if (rc < 0)
>> + return rc;
>> +
>> + if (mbox_cmd.size_out <= hdr_size) {
>> + rc = -ENXIO;
>> + goto err;
>> + }
>> +
>> + /*
>> + * Make sure retrieved out buffer is multiple of feature
>> + * entries.
>> + */
>> + retrieved = mbox_cmd.size_out - hdr_size;
>> + if (retrieved % sizeof(struct cxl_feat_entry)) {
>> + rc = -ENXIO;
>> + goto err;
>> + }
>> +
>> + /*
>> + * If the reported output entries * defined entry size !=
>> + * retrieved output bytes, then the output package is incorrect.
>> + */
>> + if (mbox_out->num_entries * feat_size != retrieved) {
>> + rc = -ENXIO;
>> + goto err;
>> + }
>> +
>> + memcpy(ptr, mbox_out->ents, retrieved);
>> + ptr += retrieved;
>> + /*
>> + * If the number of output entries is less than expected, add the
>> + * remaining entries to the next batch.
>> + */
>> + remain_feats += copy_feats - mbox_out->num_entries;
>> + start += mbox_out->num_entries;
>> + } while (remain_feats);
>> +
>> + return 0;
>> +
>> +err:
>> + cxl_mbox->num_features = 0;
>> + return rc;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_get_supported_features, CXL);
>> +
>> /**
>> * cxl_enumerate_cmds() - Enumerate commands for a device.
>> * @mds: The driver data for the operation
>> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
>> index efdf833f2c51..4d3690aa2f3b 100644
>> --- a/drivers/cxl/cxlmem.h
>> +++ b/drivers/cxl/cxlmem.h
>
>> +struct cxl_mbox_get_sup_feats_out {
>> + __le16 num_entries;
>> + __le16 supported_feats;
>> + __le32 reserved;
>> + struct cxl_feat_entry ents[] __counted_by(le32_to_cpu(supported_feats));
>
> I didn't know __counted_by worked with function calls. Interesting.

Actually I need to use __counted_by_le() instead as someone pointed out via kbot reporting.

DJ

>
>> +} __packed;
>> +
>
>> #endif /* __CXL_MEM_H__ */
>> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
>> index 7e26da706921..6a00238446f9 100644
>> --- a/drivers/cxl/pci.c
>> +++ b/drivers/cxl/pci.c
>> @@ -872,6 +872,10 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>> if (rc)
>> return rc;
>>
>> + rc = cxl_get_supported_features(&cxlds->cxl_mbox);
>
> I would separate no features from an error in trying to enumerate them.
>
>> + if (rc)
>> + dev_dbg(&pdev->dev, "No features enumerated.\n");
>> +
>> rc = cxl_set_timestamp(mds);
>> if (rc)
>> return rc;
>> diff --git a/include/linux/cxl/mailbox.h b/include/linux/cxl/mailbox.h
>> index 2380b22d7a12..570864239b8f 100644
>> --- a/include/linux/cxl/mailbox.h
>> +++ b/include/linux/cxl/mailbox.h
>> @@ -53,6 +53,7 @@ struct cxl_mbox_cmd {
>> * @mbox_mutex: mutex protects device mailbox and firmware
>> * @mbox_wait: rcuwait for mailbox
>> * @mbox_send: @dev specific transport for transmitting mailbox commands
>> + * @features: number of supported features
>
> missing docs for entries.
>
>> */
>> struct cxl_mailbox {
>> struct device *host;
>> @@ -63,6 +64,8 @@ struct cxl_mailbox {
>> struct mutex mbox_mutex; /* lock to protect mailbox context */
>> struct rcuwait mbox_wait;
>> int (*mbox_send)(struct cxl_mailbox *cxl_mbox, struct cxl_mbox_cmd *cmd);
>> + int num_features;
>> + struct cxl_feat_entry *entries;
>> };
>>
>> #endif
>> diff --git a/include/uapi/linux/cxl_mem.h b/include/uapi/linux/cxl_mem.h
>> index c6c0fe27495d..bd2535962f70 100644
>> --- a/include/uapi/linux/cxl_mem.h
>> +++ b/include/uapi/linux/cxl_mem.h
>> @@ -50,6 +50,7 @@
>> ___C(GET_LOG_CAPS, "Get Log Capabilities"), \
>> ___C(CLEAR_LOG, "Clear Log"), \
>> ___C(GET_SUP_LOG_SUBLIST, "Get Supported Logs Sub-List"), \
>> + ___C(GET_SUPPORTED_FEATURES, "Get Supported Features"), \
>> ___C(MAX, "invalid / last command")
>>
>> #define ___C(a, b) CXL_MEM_COMMAND_ID_##a
>