topic Re: Can max payload size in Device_Capabilities_Register be re-set? in Layerscape

Can max payload size in Device_Capabilities_Register be re-set?

zy_mooncity — Sat, 14 Mar 2020 03:26:37 GMT

Hi folks,

In PCIE specification, the max payload size can be one of these:

000b = 128 bytes max payload size
001b = 256 bytes max payload size
010b = 512 bytes max payload size
011b = 1KB max payload size
100b = 2KB max payload size
101b = 4KB max payload size
110b = Reserved
111b = Reserved

The max payload size field in LS1046A is 001, which is 256bytes.

In my scenario, two LS1046A boards are across connected for data transfer. One LS1046A acts as RC, the other acts as EP. In order to improve the throughput, can the field be set to other value larger than 256bytes, take example, 101b for 4K bytes?

Re: Can max payload size in Device_Capabilities_Register be re-set?

r8070z — Sat, 14 Mar 2020 06:26:47 GMT

It is impossible set to other value larger than 256bytes in the LS1046 PCI Express Device Capabilities Register.

Re: Can max payload size in Device_Capabilities_Register be re-set?

zy_mooncity — Wed, 18 Mar 2020 02:51:21 GMT

Thanks for the answer.

I just assume some read-only fields can be modified temporarily by operating DBI Read-only Write Enable Register.

So it's a design restriction for LS1046A PCI controller, and only 256Bytes capability is provided, right?

Re: Can max payload size in Device_Capabilities_Register be re-set?

r8070z — Wed, 18 Mar 2020 10:53:28 GMT

Yes, it is right.