PCI: enable extended tags support for PCIe devices
Subsystems (2)
PATCH v2 1/1 PCI: enable extended tags support for PCIe devices
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. 2.2.6.2. Transaction Descriptor ? Transaction ID Field section of the PCIe 3.1 specification describes extended tags.
32 transaction limit has been extended to 256 on PCI Express. According to the specification, all PCIe devices are required to support receiving 8-bit Tags (Tag completer). The PCIe-PCI bridges handle the translation of 8-bit tags to 5-bit tags.
However, the generation of 8-bit tags is left optional to a particular HW implementation. The code needs to check HW support before attempting to enable extended tags producer capability.
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 devices.
--- drivers/pci/probe.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
drivers/pci/probe.c +16 -0
@@ -1650,12 +1650,28 @@ static void program_hpp_type2(struct pci_dev *dev, struct hpp_type2 *hpp)*/ } +static void pci_configure_extended_tags (struct pci_dev *pdev) +{ +u32 dev_cap; +int ret; + + ret =pcie_capability_read_dword (pdev,PCI_EXP_DEVCAP , &dev_cap); + +if (ret) +return ; + +if (dev_cap &PCI_EXP_DEVCAP_EXT_TAG ) +pcie_capability_set_word (pdev,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);
Signature · 1 line
1.9.1
Hi Bjorn,
Quoted 50 lines · Sinan Kaya
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. 2.2.6.2. Transaction Descriptor ? Transaction ID Field section of the PCIe 3.1 specification describes extended tags.
32 transaction limit has been extended to 256 on PCI Express. According to the specification, all PCIe devices are required to support receiving 8-bit Tags (Tag completer). The PCIe-PCI bridges handle the translation of 8-bit tags to 5-bit tags.
However, the generation of 8-bit tags is left optional to a particular HW implementation. The code needs to check HW support before attempting to enable extended tags producer capability.
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 devices.
Signed-off-by Sinan Kaya <[email protected]>--- drivers/pci/probe.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)drivers/pci/probe.c +15
-0@@ -1650,12 +1650,28 @@ static void program_hpp_type2(struct pci_dev *dev, struct hpp_type2 *hpp)*/ } +static void pci_configure_extended_tags (struct pci_dev *pdev) +{ +u32 dev_cap; +int ret; + + ret =pcie_capability_read_dword (pdev,PCI_EXP_DEVCAP , &dev_cap); + +if (ret) +return ; + +if (dev_cap &PCI_EXP_DEVCAP_EXT_TAG ) +pcie_capability_set_word (pdev,PCI_EXP_DEVCTL , +PCI_EXP_DEVCTL_EXT_TAG ); +} +
drivers/pci/probe.c static void program_hpp_type2(struct pci_dev *dev, struct hpp_type2 *hpp) · line 1677
Quoted 10 lines
drivers/pci/probe.c +1
-0static 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);
Any feedback?
Sinan
Signature · 3 lines
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.