Subject: Re: [1/2] PCI-Express Non-Transparent Bridge Support

From: Jakub Kicinski <[email-masked]>
Date: Sun, 7 Oct 2012 14:13:44 +0200

Hi,

it's good to see some NTB code getting into mainline! I have a few comments
though.

On Tue, 02 Oct 2012 21:26:16 -0000, Jon Mason <[email-masked]>
wrote:

[...]
>+/**
>+ * ntb_write_local_spad() - write to the secondary scratchpad register
>+ * @ndev: pointer to ntb_device instance
>+ * @idx: index to the scratchpad register, 0 based
>+ * @val: the data value to put into the register
>+ *
>+ * This function allows writing of a 32bit value to the indexed scratchpad
>+ * register. The register resides on the secondary (external) side.
>+ *
>+ * RETURNS: An appropriate -ERRNO error value on error, or zero for success.
>+ */
[...]
>+/**
>+ * ntb_write_remote_spad() - write to the secondary scratchpad register
>+ * @ndev: pointer to ntb_device instance
>+ * @idx: index to the scratchpad register, 0 based
>+ * @val: the data value to put into the register
>+ *
>+ * This function allows writing of a 32bit value to the indexed scratchpad
>+ * register. The register resides on the secondary (external) side.
>+ *
>+ * RETURNS: An appropriate -ERRNO error value on error, or zero for success.
>+ */

Those comments look suspiciously similar. I think one of the functions
does write to primary scratchpad?

[...]
>+/**
>+ * ntb_read_local_spad() - read from the primary scratchpad register
>+ * @ndev: pointer to ntb_device instance
>+ * @idx: index to scratchpad register, 0 based
>+ * @val: pointer to 32bit integer for storing the register value
>+ *
>+ * This function allows reading of the 32bit scratchpad register on
>+ * the primary (internal) side.
>+ *
>+ * RETURNS: An appropriate -ERRNO error value on error, or zero for success.
>+ */
[...]
>+/**
>+ * ntb_read_remote_spad() - read from the primary scratchpad register
>+ * @ndev: pointer to ntb_device instance
>+ * @idx: index to scratchpad register, 0 based
>+ * @val: pointer to 32bit integer for storing the register value
>+ *
>+ * This function allows reading of the 32bit scratchpad register on
>+ * the primary (internal) side.
>+ *
>+ * RETURNS: An appropriate -ERRNO error value on error, or zero for success.
>+ */

Same here.

[...]
>+static int ntb_setup_msix(struct ntb_device *ndev)
>+{
>+	struct pci_dev *pdev = ndev->pdev;
>+	struct msix_entry *msix;
>+	int msix_entries;
>+	int rc, i, pos;
>+	u16 val;
>+
>+	pos = pci_find_capability(pdev, PCI_CAP_ID_MSIX);
>+	if (!pos) {
>+		rc = -EIO;
>+		goto err;
>+	}
>+
>+	rc = pci_read_config_word(pdev, pos + PCI_MSIX_FLAGS, &val);
>+	if (rc)
>+		goto err;
>+
>+	msix_entries = msix_table_size(val);
>+	if (msix_entries > ndev->limits.msix_cnt) {
>+		rc = -EINVAL;
>+		goto err;
>+	}
>+
>+	ndev->msix_entries = kmalloc(sizeof(struct msix_entry) * msix_entries,
>+				     GFP_KERNEL);
>+	if (!ndev->msix_entries) {
>+		rc = -ENOMEM;
>+		goto err;
>+	}
>+
>+	for (i = 0; i < msix_entries; i++)
>+		ndev->msix_entries[i].entry = i;
>+
>+	rc = pci_enable_msix(pdev, ndev->msix_entries, msix_entries);
>+	if (rc < 0)
>+		goto err1;
>+	if (rc > 0) {

rc > 0 doesn't mean that vectors were allocated. Have a look at the
example in Documentation/PCI/MSI-HOWTO.txt.

>+		/* On SNB, the link interrupt is always tied to 4th vector.  If
>+		 * we can't get all 4, then we can't use MSI-X.
>+		 */
>+		if (ndev->hw_type != BWD_HW) {
>+			rc = -EIO;
>+			goto err1;
>+		}

This looks fragile, what if msix_table_size(val) was < 4? 

>+
>+		dev_warn(&pdev->dev,
>+			 "Only %d MSI-X vectors.  Limiting the number of queues to that number.\n",
>+			 rc);
>+		msix_entries = rc;
>+	}
>+
>+	for (i = 0; i < msix_entries; i++) {
>+		msix = &ndev->msix_entries[i];
>+		WARN_ON(!msix->vector);
>+
>+		/* Use the last MSI-X vector for Link status */
>+		if (ndev->hw_type == BWD_HW) {
>+			rc = request_irq(msix->vector, bwd_callback_msix_irq, 0,
>+					 "ntb-callback-msix", &ndev->db_cb[i]);
>+			if (rc)
>+				goto err2;
>+		} else {
>+			if (i == msix_entries - 1) {
>+				rc = request_irq(msix->vector,
>+						 xeon_event_msix_irq, 0,
>+						 "ntb-event-msix", ndev);
>+				if (rc)
>+					goto err2;
>+			} else {
>+				rc = request_irq(msix->vector,
>+						 xeon_callback_msix_irq, 0,
>+						 "ntb-callback-msix",
>+						 &ndev->db_cb[i]);
>+				if (rc)
>+					goto err2;
>+			}
>+		}
>+	}
>+
>+	ndev->num_msix = msix_entries;
>+	if (ndev->hw_type == BWD_HW)
>+		ndev->max_cbs = msix_entries;
>+	else
>+		ndev->max_cbs = msix_entries - 1;
>+
>+	return 0;
>+
>+err2:
>+	while (--i >= 0) {
>+		msix = &ndev->msix_entries[i];
>+		if (ndev->hw_type != BWD_HW && i == ndev->num_msix - 1)
>+			free_irq(msix->vector, ndev);
>+		else
>+			free_irq(msix->vector, &ndev->db_cb[i]);
>+	}
>+	pci_disable_msix(pdev);
>+err1:
>+	kfree(ndev->msix_entries);
>+	dev_err(&pdev->dev, "Error allocating MSI-X interrupt\n");
>+err:
>+	ndev->num_msix = 0;
>+	return rc;
>+}

Thanks for your work,

  -- Kuba