docs/acpi/bits: add some clarity and details while also improving formating

Update bios-bits docs to add more details on why a pre-OS environment for
testing bioses is useful. Add author's FOSDEM talk link. Also improve the
formating of the document while at it.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

docs/devel/acpi-bits.rst

@@ -1,26 +1,48 @@
 =============================================================================
 ACPI/SMBIOS avocado tests using biosbits
 =============================================================================
-
+************
+Introduction
+************
 Biosbits is a software written by Josh Triplett that can be downloaded
 from https://biosbits.org/. The github codebase can be found
-`here <https://github.com/biosbits/bits/tree/master>`__. It is a software that executes
-the bios components such as acpi and smbios tables directly through acpica
-bios interpreter (a freely available C based library written by Intel,
+`here <https://github.com/biosbits/bits/tree/master>`__. It is a software that
+executes the bios components such as acpi and smbios tables directly through
+acpica bios interpreter (a freely available C based library written by Intel,
 downloadable from https://acpica.org/ and is included with biosbits) without an
-operating system getting involved in between.
+operating system getting involved in between. Bios-bits has python integration
+with grub so actual routines that executes bios components can be written in
+python instead of bash-ish (grub's native scripting language).
 There are several advantages to directly testing the bios in a real physical
-machine or VM as opposed to indirectly discovering bios issues through the
-operating system. For one thing, the OSes tend to hide bios problems from the
-end user. The other is that we have more control of what we wanted to test
-and how by directly using acpica interpreter on top of the bios on a running
-system. More details on the inspiration for developing biosbits and its real
-life uses can be found in [#a]_ and [#b]_.
+machine or in a VM as opposed to indirectly discovering bios issues through the
+operating system (the OS). Operating systems tend to bypass bios problems and
+hide them from the end user. We have more control of what we wanted to test and
+how by being as close to the bios on a running system as possible without a
+complicated software component such as an operating system coming in between.
+Another issue is that we cannot exercise bios components such as ACPI and
+SMBIOS without being in the highest hardware privilege level, ring 0 for
+example in case of x86. Since the OS executes from ring 0 whereas normal user
+land software resides in unprivileged ring 3, operating system must be modified
+in order to write our test routines that exercise and test the bios. This is
+not possible in all cases. Lastly, test frameworks and routines are preferably
+written using a high level scripting language such as python. OSes and
+OS modules are generally written using low level languages such as C and
+low level assembly machine language. Writing test routines in a low level
+language makes things more cumbersome. These and other reasons makes using
+bios-bits very attractive for testing bioses. More details on the inspiration
+for developing biosbits and its real life uses can be found in [#a]_ and [#b]_.
+
 For QEMU, we maintain a fork of bios bits in gitlab along with all the
-dependent submodules here: https://gitlab.com/qemu-project/biosbits-bits
+dependent submodules `here <https://gitlab.com/qemu-project/biosbits-bits>`__.
 This fork contains numerous fixes, a newer acpica and changes specific to
 running this avocado QEMU tests using bits. The author of this document
-is the sole maintainer of the QEMU fork of bios bits repo.
+is the sole maintainer of the QEMU fork of bios bits repository. For more
+information, please see author's `FOSDEM talk on this bios-bits based test
+framework <https://fosdem.org/2024/schedule/event/fosdem-2024-2262-exercising-qemu-generated-acpi-smbios-tables-using-biosbits-from-within-a-guest-vm-/>`__.
+
+*********************************
+Description of the test framework
+*********************************
 
 Under the directory ``tests/avocado/``, ``acpi-bits.py`` is a QEMU avocado
 test that drives all this.
@@ -120,8 +142,9 @@ Under ``tests/avocado/`` as the root we have:
        (b) Add a SPDX license header.
        (c) Perform modifications to the test.
 
-   Commits (a), (b) and (c) should go under separate commits so that the original
-   test script and the changes we have made are separated and clear.
+   Commits (a), (b) and (c) preferably should go under separate commits so that
+   the original test script and the changes we have made are separated and
+   clear. (a) and (b) can sometimes be combined into a single step.
 
    The test framework will then use your modified test script to run the test.
    No further changes would be needed. Please check the logs to make sure that
@@ -141,4 +164,4 @@ References:
 -----------
 .. [#a] https://blog.linuxplumbersconf.org/2011/ocw/system/presentations/867/original/bits.pdf
 .. [#b] https://www.youtube.com/watch?v=36QIepyUuhg
-
+.. [#c] https://fosdem.org/2024/schedule/event/fosdem-2024-2262-exercising-qemu-generated-acpi-smbios-tables-using-biosbits-from-within-a-guest-vm-/