Re: [RESEND PATCH V3 6/6] PCI: Enable 10-Bit tag support for PCIe RP devices

On 2021/6/14 13:57, Christoph Hellwig wrote:

On Sun, Jun 13, 2021 at 05:29:15PM +0800, Dongdong Liu wrote:

quoted

PCIe spec 5.0r1.0 section 2.2.6.2 implementation note, In configurations
where a Requester with 10-Bit Tag Requester capability needs to target
multiple Completers, one needs to ensure that the Requester sends 10-Bit
Tag Requests only to Completers that have 10-Bit Tag Completer capability.
So we enable 10-Bit Tag Requester for root port only when the devices
under the root port support 10-Bit Tag Completer.

Signed-off-by: Dongdong Liu <redacted>
---
 drivers/pci/pcie/portdrv_pci.c | 75 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
index c7ff1ee..baf413f 100644
--- a/drivers/pci/pcie/portdrv_pci.c
+++ b/drivers/pci/pcie/portdrv_pci.c

@@ -90,6 +90,78 @@ static const struct dev_pm_ops pcie_portdrv_pm_ops = {
 #define PCIE_PORTDRV_PM_OPS	NULL
 #endif /* !PM */

+static int pci_10bit_tag_comp_support(struct pci_dev *dev, void *data)
+{
+	u8 *support = data;
+
+	if (*support == 0)
+		return 0;
+
+	if (!pci_is_pcie(dev)) {
+		*support = 0;
+		return 0;
+	}
+
+	/*
+	 * PCIe spec 5.0r1.0 section 2.2.6.2 implementation note.
+	 * For configurations where a Requester with 10-Bit Tag Requester
+	 * capability targets Completers where some do and some do not have
+	 * 10-Bit Tag Completer capability, how the Requester determines which
+	 * NPRs include 10-Bit Tags is outside the scope of this specification.
+	 * So we do not consider hotplug scenario.
+	 */
+	if (dev->is_hotplug_bridge) {
+		*support = 0;
+		return 0;
+	}
+
+	if (!(dev->pcie_devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_COMP)) {
+		*support = 0;
+		return 0;
+	}
+
+	return 0;
+}
+
+static void pci_configure_rp_10bit_tag(struct pci_dev *dev)
+{
+	u8 support = 1;
+	struct pci_dev *pchild;
+
+	if (dev->subordinate == NULL)
+		return;
+
+	/* If no devices under the root port, no need to enable 10-Bit Tag. */
+	pchild = list_first_entry_or_null(&dev->subordinate->devices,
+					  struct pci_dev, bus_list);
+	if (pchild == NULL)
+		return;

pchild is never used after this check, so this could be simplified to
a list_empty(&dev->subordinate->devices).

Good point, will do.

Thanks,
Dongdong

.