On Tue, Apr 19, 2022 at 12:45:03PM -0700, Dan Williams wrote: > On Tue, Apr 19, 2022 at 9:48 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Tue, Apr 19, 2022 at 09:38:50AM -0700, Tony Luck wrote: > > > Add documentation for In-Field Scan (IFS). This documentation > > > describes the basics of IFS, the loading IFS image, chunk > > > authentication, running scan and how to check result via sysfs > > > as well as tunable parameters. > > > > > > The CORE_CAPABILITIES MSR enumerates whether IFS is supported. > > > > > > The full github location for distributing the IFS images is > > > still being decided. So just a placeholder included for now > > > in the documentation. > > > > > > Future CPUs will support more than one type of test. Plan for > > > that now by using a ".0" suffix on the ABI directory names. > > > Additional test types will use ".1", etc. > > > > > > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx> > > > Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx> > > > --- > > > Documentation/x86/ifs.rst | 101 ++++++++++++++++++++++++++++++++++++ > > > Documentation/x86/index.rst | 1 + > > > 2 files changed, 102 insertions(+) > > > create mode 100644 Documentation/x86/ifs.rst > > > > > > diff --git a/Documentation/x86/ifs.rst b/Documentation/x86/ifs.rst > > > new file mode 100644 > > > index 000000000000..62f3c07d433a > > > --- /dev/null > > > +++ b/Documentation/x86/ifs.rst > > > @@ -0,0 +1,101 @@ > > > +.. SPDX-License-Identifier: GPL-2.0 > > > + > > > +============= > > > +In-Field Scan > > > +============= > > > + > > > +Introduction > > > +------------ > > > + > > > +In Field Scan (IFS) is a hardware feature to run circuit level tests on > > > +a CPU core to detect problems that are not caught by parity or ECC checks. > > > +Future CPUs will support more than one type of test which will show up > > > +with a new platform-device instance-id, for now only .0 is exposed. > > > + > > > + > > > +IFS Image > > > +--------- > > > + > > > +Intel provides a firmware file containing the scan tests via > > > +github [#f1]_. Similar to microcode there is a separate file for each > > > +family-model-stepping. > > > + > > > +IFS Image Loading > > > +----------------- > > > + > > > +The driver loads the tests into memory reserved BIOS local to each CPU > > > +socket in a two step process using writes to MSRs to first load the > > > +SHA hashes for the test. Then the tests themselves. Status MSRs provide > > > +feedback on the success/failure of these steps. When a new test file > > > +is installed it can be loaded by writing to the driver reload file:: > > > + > > > + # echo 1 > /sys/bus/platform/drivers/intel_ifs.0/reload > > > + > > > +Similar to microcode, the current version of the scan tests is stored > > > +in a fixed location: /lib/firmware/intel/ifs.0/family-model-stepping.scan > > > + > > > +Running tests > > > +------------- > > > + > > > +Tests are run by the driver synchronizing execution of all threads on a > > > +core and then writing to the ACTIVATE_SCAN MSR on all threads. Instruction > > > +execution continues when: > > > + > > > +1) All tests have completed. > > > +2) Execution was interrupted. > > > +3) A test detected a problem. > > > + > > > +In all cases reading the SCAN_STATUS MSR provides details on what > > > +happened. The driver makes the value of this MSR visible to applications > > > +via the "details" file (see below). Interrupted tests may be restarted. > > > + > > > +The IFS driver provides sysfs interfaces via /sys/devices/platform/intel_ifs.0/ > > > +to control execution: > > > + > > > +Test a specific core:: > > > + > > > + # echo <cpu#> > /sys/devices/platform/intel_ifs.0/run_test > > > + > > > +when HT is enabled any of the sibling cpu# can be specified to test its > > > +corresponding physical core. Since the tests are per physical core, the > > > +result of testing any thread is same. It is only necessary to test one > > > +thread. > > > + > > > +For e.g. to test core corresponding to cpu5 > > > + > > > + # echo 5 > /sys/devices/platform/intel_ifs.0/run_test > > > + > > > +Results of the last test is provided in /sys:: > > > + > > > + $ cat /sys/devices/platform/intel_ifs.0/status > > > + pass > > > > sysfs documentation belongs in Documentation/ABI/ > > > > And why not just include this whole thing in the driver itself and suck > > the documentation out of that? No need to have a separate file. > > At a minimum a separate file is needed to house the > --- > .. kernel-doc:: $source_file > :doc: $header > --- > ...statements, but ok, I'll recommend that going forward to > de-emphasize shipping content directly from Documentation/ when it can > be ingested from "DOC:" source. I had been assuming DOC: blocks in the > code were more for augmenting kernel-doc on driver internal ABIs and > not longer theory of operation documentation that is an awkward fit > for Documentation/ABI/. I don't know which is better, it's just that creating a whole new documentation file for a single tiny driver feels very odd as it will get out of date and is totally removed from the driver itself. I'd prefer that drivers be self-contained, including the documentation, as it is much more obvious what is happening with that. Spreading stuff around the tree only causes stuff to get out of sync easier. thanks, greg k-h
