Hi,
On 04/02/2024 09:40, Peng Fan wrote:
-----Original Message-----
From: Julien Grall <jul...@xen.org>
Sent: 2024年2月2日 17:20
To: John Ernberg <john.ernb...@actia.se>; Stefano Stabellini
<sstabell...@kernel.org>; Bertrand Marquis <bertrand.marq...@arm.com>;
Michal Orzel <michal.or...@amd.com>; Volodymyr Babchuk
<volodymyr_babc...@epam.com>; Peng Fan <peng....@nxp.com>
Cc: Jonas Blixt <jonas.bl...@actia.se>; xen-devel@lists.xenproject.org
Subject: Re: [PATCH 1/2] xen/arm: Add imx8q{m,x} platform glue
On 01/02/2024 16:17, John Ernberg wrote:
On 2/1/24 13:20, Julien Grall wrote:
On 31/01/2024 15:32, John Ernberg wrote:
Hi Julien,
Hi John,
On 1/31/24 13:22, Julien Grall wrote:
Hi,
On 31/01/2024 11:50, John Ernberg wrote:
When using Linux for dom0 there are a bunch of drivers that need
to do SMC SIP calls into the PSCI provider to enable certain
hardware bits like the watchdog.
Do you know which protocol this is under the hood. Is this SCMI?
I think I confused myself here when I wrote the commit log.
The EL3 code in our case is ATF, and it does not appear to be SCMI,
nor PSCI. The register usage of these SMC SIP calls are as follows:
a0 - service
a1 - function
a2-a7 - args
In ATF the handler is declared as a runtime service.
Would the appropriate commmit message here be something along the
lines of below?
"""
When using Linux for dom0 there are a bunch of drivers that need to
do SMC SIP calls into the firmware to enable certain hardware bits
like the watchdog.
"""
It reads better thanks.
[...]
But even if we restrict to dom0, have you checked that none of the
SMCs use buffers?
I haven't found any such instances in the Linux kernel where a
buffer is used. Adding a call filtering like suggested below
additions of such functions can be discovered and adapted for if they
would show up later.
Rather than providing a blanket forward, to me it sounds more like
you want to provide an allowlist of the SMCs. This is more
futureproof and avoid the risk to expose unsafe SMCs to any domain.
For an example, you can have a look at the EEMI mediator for Xilinx.
Ack. Do you prefer to see only on SMCCC service level or also on
function level? (a1 register, per description earlier)
I am not sure. It will depend on whether it is correct to expose
*all* the functions within a service level and they have the same format.
If you can't guarantee that, then you will most likely need to
allowlist at the function level.
Also, do you have a spec in hand that would help to understand which
service/function is implemented via those SMCs?
I don't have the spec unfortunately, but I will add a filter on both
service and function for V2 and we'll take it from there.
@Peng, do you have any specification you could share? How stable is the
interface?
No specification, the use is IMX_SIP_X in linux kernel source.
Such as IMX_SIP_RTC, IMX_SIP_TIMER
It is stable and no change, we only add new SIP macro if needed
and no change the meaning or reuse old SIP.
Thanks for the answer. It is a bit unfortunate there are no
specification, but at least they are stable.
I have searched IMX_SIP in Linux, there doesn't seem many so we could
allowlist them (see more below). Do you know if there are more necessary
that are not yet upstreamed in Linux?
Looking through the list, there are some that probably want a bit more
discussion on whether we want to expose them:
* IMX_SIP_CPUFREQ: Right now, dom0 is not aware of the full system.
So it may take wrong decision.
* IMX_SIP_DDR_DVFS: Some operation seems to take the number of online
CPUs. Dom0 doesn't know that
* IMX_SIP_TIMER_*: This seems to be related to the watchdog.
Shouldn't dom0 rely on the watchdog provided by Xen instead? So those
call will be used by Xen.
Also, what happen if we don't expose those SMC to dom0?
Cheers,
--
Julien Grall
