CTLE has two settings, HG (High Gain) mode and HDR (High Data Rate) mode. Which setting should I use when using PCIe (PCI-Express) IP with Arria® 10?

When using PCIe IP, HG mode is applied by default.
HDR mode can be selected for high bandwidths exceeding 17.4Gbps.
HG mode is recommended for lower bandwidths.

(Reference) Intel Arria 10 Transceiver PHY User Guide
https://www.intel.com/content/www/us/en/programmable/documentation/nik1398707230472.html#nik1398707104770
(see 5.1.5.4. Continuous Time Linear Equalization (CTLE) section)

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Category: PCI-Express
Tool: Quartus® Prime
Device: Arria® 10