On 09/09/2024 10:50, Ayan Kumar Halder wrote:
On 09/09/2024 10:11, Julien Grall wrote:
On 09/09/2024 09:56, Michal Orzel wrote:
Hi Julien,
On 08/09/2024 23:05, Julien Grall wrote:
Hi Ayan,
On 06/09/2024 11:13, Ayan Kumar Halder wrote:
From: Michal Orzel <michal.or...@amd.com>
AOU are the assumptions Xen relies on other components (eg
platform, domains)
Searching online, I think the abbrevition is AoU rather than AOU. This
would also match how we abbreviate in Xen (IOW if we use a lower case
letter from the expanded name, then the letter in the acronym is also
lower case).
to fulfill its requirements. In our case, platform means a
combination of
hardware, firmware and bootloader.
We have defined AOU in the intro.rst and added AOU for the generic
timer.
Signed-off-by: Michal Orzel <michal.or...@amd.com>
Signed-off-by: Ayan Kumar Halder <ayan.kumar.hal...@amd.com>
---
.../reqs/design-reqs/arm64/generic-timer.rst | 19 +++++++++++++
++++++
docs/fusa/reqs/intro.rst | 10 ++++++++++
2 files changed, 29 insertions(+)
diff --git a/docs/fusa/reqs/design-reqs/arm64/generic-timer.rst b/
docs/fusa/reqs/design-reqs/arm64/generic-timer.rst
index f2a0cd7fb8..9df87cf4e0 100644
--- a/docs/fusa/reqs/design-reqs/arm64/generic-timer.rst
+++ b/docs/fusa/reqs/design-reqs/arm64/generic-timer.rst
@@ -116,6 +116,25 @@ Rationale:
Comments:
+Covers:
+ - `XenProd~emulated_timer~1`
+
+Assumption of Use on the Platform
+=================================
+
+Expose system timer frequency via register
+------------------------------------------
+
+`XenSwdgn~arm64_generic_timer_pf_program_cntfrq_el0~1`
+
+Description:
+Underlying platform shall ensure that CNTFRQ_EL0 register contains
the system
+timer frequency.
The wording in [1] (not yet merged) implies that CNTFRQ_EL0 may be
It is merged:
https://xenbits.xen.org/gitweb/?
p=xen.git;a=commit;h=51ad2c57a2d21b583a5944a0dc21c709af022f3c
invalid. This seems to contradict the Assumption of Use. Can you
explain
the difference?
The requirement you refer to is written from a domain perspective and
is about Xen exposing the frequency
to domains via CNTFRQ and/or dt property. In case of a presence of dt
property in the host dtb, Xen could for instance decide
to emulate CNTFRQ instead of relying on the domain to parse the dt at
runtime.
AFAICT, you can't trap CNTFRQ access. So what you suggest would not work.
The AoU on the platform (hw/firmware/bootloader) is written from Xen
perspective and is about the platform
exposing the correct frequency via register. This is Xen expected
behavior on the platform. In other words, the platform should
expose the correct frequency via register.
Xen is able to deal with broken CNTFRQ_EL0.
Yes, this is correct if the user provides "clock-frequency" dt property.
So I don't understand why we we would want to make an assumption that
it shall not be broken. What do you gain?
Refer https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
linux.git/tree/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml
```
Use of this property is strongly discouraged; fix your firmware unless
absolutely impossible.
```
We wish to put the onus on the platform/firmware provider to program the
register correctly. Otherwise, we will have to document it somewhere
(may be safety manual) that User needs to provide the "clock-frequency"
dt property.
I think you will have to. The integrator may not have the possibility to
modify the firmware.
We wish to put as little responsibility on the user as
possible(especially when the dt documentation discourages it as well).
I think there are some contradiction with the requirements. I understand
they are for the guest interface only but, if I am not mistaken, the
only way the "clock-frequency" can be visible to the guest is because it
is part of the host DT.
Furthermore, as soon as the property is specified, then Xen will ignore
the value from CNTFRQ_EL0. So if we want to push the firmware vendor to
expose a valid CNTFREQ_EL0, then I don't understand why we would want to
mention the property in the requirements.
Cheers,
--
Julien Grall
