On Thu, Sep 05, 2024 at 09:46:44AM -0500, Wei Huang wrote:

On 9/4/24 14:40, Bjorn Helgaas wrote:

quoted

On Thu, Aug 22, 2024 at 03:41:11PM -0500, Wei Huang wrote:

quoted

Add pcie_tph_modes() to allow drivers to query the TPH modes supported
by an endpoint device, as reported in the TPH Requester Capability
register. The modes are reported as a bitmask and current supported
modes include:

 - PCI_TPH_CAP_NO_ST: NO ST Mode Supported
 - PCI_TPH_CAP_INT_VEC: Interrupt Vector Mode Supported
 - PCI_TPH_CAP_DEV_SPEC: Device Specific Mode Supported

quoted

+ * pcie_tph_modes - Get the ST modes supported by device
+ * @pdev: PCI device
+ *
+ * Returns a bitmask with all TPH modes supported by a device as shown in the
+ * TPH capability register. Current supported modes include:
+ *   PCI_TPH_CAP_NO_ST - NO ST Mode Supported
+ *   PCI_TPH_CAP_INT_VEC - Interrupt Vector Mode Supported
+ *   PCI_TPH_CAP_DEV_SPEC - Device Specific Mode Supported
+ *
+ * Return: 0 when TPH is not supported, otherwise bitmask of supported modes
+ */
+int pcie_tph_modes(struct pci_dev *pdev)
+{
+	if (!pdev->tph_cap)
+		return 0;
+
+	return get_st_modes(pdev);
+}
+EXPORT_SYMBOL(pcie_tph_modes);

I'm not sure I see the need for pcie_tph_modes().  The new bnxt code
looks like this:

  bnxt_request_irq
    if (pcie_tph_modes(bp->pdev) & PCI_TPH_CAP_INT_VEC)
      rc = pcie_enable_tph(bp->pdev, PCI_TPH_CAP_INT_VEC);

What is the advantage of this over just this?

  bnxt_request_irq
    rc = pcie_enable_tph(bp->pdev, PCI_TPH_CAP_INT_VEC);

It seems like drivers could just ask for what they want since
pcie_enable_tph() has to verify support for it anyway.  If that fails,
the driver can fall back to another mode.

I can get rid of pcie_tph_modes() if unnecessary.

The design logic was that a driver can be used on various devices from
the same company. Some of these devices might not be TPH capable. So
instead of using trial-and-error (i.e. try INT_VEC ==> DEV_SPEC ==> give
up), we provide a way for the driver to query the device TPH
capabilities and pick a mode explicitly. IMO the code will be a bit cleaner.

quoted

Returning a bitmask of supported modes might be useful if the driver
could combine them, but IIUC the modes are all mutually exclusive, so
the driver can't request a combination of them.

In the real world cases I saw, this is true. In the spec I didn't find
that these bits are mutually exclusive though.

A device may advertise *support* for multiple modes in TPH Requester
Capability, of course.  

What I meant by "driver can't request a combination" is that we can
only *select* one of them via the ST Mode select in TPH Requester
Control.