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[ Upstream commitf89c7fb83a] On RK3588 with LPDDR4X memory, the cycle count as returned by perf stat -a -e rockchip_ddr/cycles/ sleep 1 consistently reads half as much as what the actual DDR frequency is at. For a LPDDR4X module running at 2112MHz, I get more like 1056059916 cycles per second, which is almost bang-on half what it should be. No, I'm not mixing up megatransfers and megahertz. Consulting the downstream driver, this appears to be because the RK3588 hardware specifically (and RK3528 as well, for future reference) needs a multiplier of 2 to get to the correct frequency with everything but LPDDR5. The RK3588's actual memory bandwidth measurements in MB/s are correct however, as confirmed with stress-ng --stream. This makes me think the access counters are not affected in the same way. This tracks with the vendor kernel not multiplying the access counts either. Solve this by adding a new member to the dfi struct, which each SoC can set to whatever they want, but defaults to 1 if left unset by the SoC init functions. The event_get_count op can then use this multiplier if the cycle count is requested. The cycle multiplier is not used in rockchip_dfi_get_event because the vendor driver doesn't use it there either, and we don't do other actual bandwidth unit conversion stuff in there anyway. Fixes:481d97ba61("PM / devfreq: rockchip-dfi: add support for RK3588") Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com> Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com> Link: https://lore.kernel.org/lkml/20250530-rk3588-dfi-improvements-v1-1-6e077c243a95@collabora.com/ Signed-off-by: Sasha Levin <sashal@kernel.org>
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 reStructuredText 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.