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Turns out our skills in decoding the CLKCFG register weren't good enough. On this particular elk the answer we got was 400 MHz when in reality the clock was running at 266 MHz, which then caused us to program a bogus AUX clock divider that caused all AUX communication to fail. Sadly the docs are now in bit heaven, so the fix will have to be based on empirical evidence. Using another elk machine I was able to frob the FSB frequency from the BIOS and see how it affects the CLKCFG register. The machine seesm to use a frequency of 266 MHz by default, and fortunately it still boot even with the 50% CPU overclock that we get when we bump the FSB up to 400 MHz. It turns out the actual FSB frequency and the register have no real link whatsoever. The register value is based on some straps or something, but fortunately those too can be configured from the BIOS on this board, although it doesn't seem to respect the settings 100%. In the end I was able to derive the following relationship: BIOS FSB / strap | CLKCFG ------------------------- 200 | 0x2 266 | 0x0 333 | 0x4 400 | 0x4 So only the 200 and 400 MHz cases actually match how we're currently decoding that register. But as the comment next to some of the defines says, we have been just guessing anyway. So let's fix things up so that at least the 266 MHz case will work correctly as that is actually the setting used by both the buggy machine and my test machine. The fact that 333 and 400 MHz BIOS settings result in the same register value is a little disappointing, as that means we can't tell them apart. However, according to the gmch datasheet for both elk and ctg 400 Mhz is not even a supported FSB frequency, so I'm going to make the assumption that we should decode it as 333 MHz instead. Cc: stable@vger.kernel.org Cc: Tomi Sarvela <tomi.p.sarvela@intel.com> Reported-by: Tomi Sarvela <tomi.p.sarvela@intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100926 Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170504181530.6908-1-ville.syrjala@linux.intel.com Acked-by: Jani Nikula <jani.nikula@intel.com> Tested-by: Tomi Sarvela <tomi.p.sarvela@intel.com> (cherry picked from commit 6f38123ecaac446312a63523b68df84ceb5a06ed) Signed-off-by: Jani Nikula <jani.nikula@intel.com>
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.