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8efbdbfa99
Initialize MAC_ONEUS_TIC_COUNTER register with correct value derived
from CSR clock, otherwise EEE is unstable on at least NXP i.MX8M Plus
and Micrel KSZ9131RNX PHY, to the point where not even ARP request can
be sent out.
i.MX 8M Plus Applications Processor Reference Manual, Rev. 1, 06/2021
11.7.6.1.34 One-microsecond Reference Timer (MAC_ONEUS_TIC_COUNTER)
defines this register as:
"
This register controls the generation of the Reference time (1 microsecond
tic) for all the LPI timers. This timer has to be programmed by the software
initially.
...
The application must program this counter so that the number of clock cycles
of CSR clock is 1us. (Subtract 1 from the value before programming).
For example if the CSR clock is 100MHz then this field needs to be programmed
to value 100 - 1 = 99 (which is 0x63).
This is required to generate the 1US events that are used to update some of
the EEE related counters.
"
The reset value is 0x63 on i.MX8M Plus, which means expected CSR clock are
100 MHz. However, the i.MX8M Plus "enet_qos_root_clk" are 266 MHz instead,
which means the LPI timers reach their count much sooner on this platform.
This is visible using a scope by monitoring e.g. exit from LPI mode on TX_CTL
line from MAC to PHY. This should take 30us per STMMAC_DEFAULT_TWT_LS setting,
during which the TX_CTL line transitions from tristate to low, and 30 us later
from low to high. On i.MX8M Plus, this transition takes 11 us, which matches
the 30us * 100/266 formula for misconfigured MAC_ONEUS_TIC_COUNTER register.
Configure MAC_ONEUS_TIC_COUNTER based on CSR clock, so that the LPI timers
have correct 1us reference. This then fixes EEE on i.MX8M Plus with Micrel
KSZ9131RNX PHY.
Fixes:
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.