80d7d7a904
Per PCIe r3.1, sec 5.5.1, LTR_L1.2_THRESHOLD determines whether we enter
the L1.2 Link state: if L1.2 is enabled and downstream devices have
reported that they can tolerate latency of at least LTR_L1.2_THRESHOLD, we
must enter L1.2 when CLKREQ# is de-asserted.
The implication is that LTR_L1.2_THRESHOLD is the time required to
transition the Link from L0 to L1.2 and back to L0, and per sec 5.5.3.3.1,
Figures 5-16 and 5-17, it appears that the absolute minimum time for those
transitions would be T(POWER_OFF) + T(L1.2) + T(POWER_ON) + T(COMMONMODE).
Therefore, compute LTR_L1.2_THRESHOLD as:
2us T(POWER_OFF)
+ 4us T(L1.2)
+ T(POWER_ON)
+ T(COMMONMODE)
= LTR_L1.2_THRESHOLD
Previously we set LTR_L1.2_THRESHOLD to a fixed value of 163840ns
(163.84us):
#define LTR_L1_2_THRESHOLD_BITS ((1 << 21) | (1 << 23) | (1 << 30))
((1 << 21) | (1 << 23) | (1 << 30)) = 0x40a00000
LTR_L1.2_THRESHOLD_Value = (0x40a00000 & 0x03ff0000) >> 16 = 0xa0 = 160
LTR_L1.2_THRESHOLD_Scale = (0x40a00000 & 0xe0000000) >> 29 = 0x2 (* 1024ns)
LTR_L1.2_THRESHOLD = 160 * 1024ns = 163840ns
Obviously this doesn't account for the circuit characteristics of different
implementations.
Note that while firmware may enable LTR, Linux itself currently does not
enable LTR. When L1.2 is enabled but LTR is not, LTR_L1.2_THRESHOLD is
ignored and we always enter L1.2 when it is enabled and CLKREQ# is
de-asserted. So this patch should not have any effect unless firmware
enables LTR.
Fixes:
|
||
|---|---|---|
| Documentation | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.