On Thu, Nov 10, 2016 at 01:35:41PM -0500, Sinan Kaya wrote:

On 9/24/2016 10:10 PM, Sinan Kaya wrote:

quoted

Each PCIe device can issue up to 32 transactions at a time by default.
Each transaction is tracked by a tag number on the bus. 32 outstanding
transactions is not enough for some performance critical applications
especially when a lot of small sized frames are transmitted.

Extended tags support increases this number to 256. Devices not
supporting extended tags tie-off this field to 0. According to ECN, it
is safe to enable this feature for all PCIe endpoints.

Signed-off-by: Sinan Kaya <redacted>
---
 drivers/pci/probe.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 93f280d..2424f38 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c

@@ -1505,12 +1505,19 @@ static void program_hpp_type2(struct pci_dev *dev, struct hpp_type2 *hpp)
 	 */
 }
 
+static int pci_configure_extended_tags(struct pci_dev *dev)
+{

I should have checked the capability here before trying to enable it. 
I'll post a follow up patch on this. 

Is there any other feedback?

If this were completely safe to enable for every device that supported
it, why would there be an enable bit in Device Control?

I don't know anything about extended tags, but it worries me a little
when there's a "go-fast" switch and no explanation about when and why
we might need to go slow.

quoted

+	return pcie_capability_set_word(dev, PCI_EXP_DEVCTL,
+					 PCI_EXP_DEVCTL_EXT_TAG);
+}
+
 static void pci_configure_device(struct pci_dev *dev)
 {
 	struct hotplug_params hpp;
 	int ret;
 
 	pci_configure_mps(dev);
+	pci_configure_extended_tags(dev);
 
 	memset(&hpp, 0, sizeof(hpp));
 	ret = pci_get_hp_params(dev, &hpp);

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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