From: Valentin Schneider <valentin.schneider@arm.com>
To: Ruifeng Zhang <ruifeng.zhang0110@gmail.com>
Cc: linux@armlinux.org.uk, sudeep.holla@arm.com,
Greg KH <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
a.p.zijlstra@chello.nl, dietmar.eggemann@arm.com,
mingo@kernel.org, ruifeng.zhang1@unisoc.com,
nianfu.bai@unisoc.com, linux-arm-kernel@lists.infradead.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/1] arm: topology: parse the topology from the dt
Date: Mon, 12 Apr 2021 16:32:57 +0100 [thread overview]
Message-ID: <87tuobmsba.mognet@arm.com> (raw)
In-Reply-To: <CAG7+-3MsjuChoEOj11VAMX9W61UY6MmphkxWDF=-_R1A8sfvpA@mail.gmail.com>
On 12/04/21 20:20, Ruifeng Zhang wrote:
> There is a armv8.3 cpu which should work normally both on aarch64 and aarch32.
> The MPIDR has been written to the chip register in armv8.3 format.
> For example,
> core0: 0000000080000000
> core1: 0000000080000100
> core2: 0000000080000200
> ...
>
> Its cpu topology can be parsed normally on aarch64 mode (both
> userspace and kernel work on arm64).
>
> The problem is when it working on aarch32 mode (both userspace and
> kernel work on arm 32-bit),
I didn't know using aarch32 elsewhere than EL0 was something actually being
used. Do you deploy this somewhere, or do you use it for testing purposes?
> the cpu topology
> will parse error because of the format is different between armv7 and armv8.3.
> The arm 32-bit driver, arch/arm/kernel/topology will parse the MPIDR
> and store to the topology with armv7,
> and the result is all cpu core_id is 0, the bit[1:0] of armv7 MPIDR format.
>
I'm not fluent at all in armv7 (or most aarch32 compat mode stuff), but
I couldn't find anything about MPIDR format differences:
DDI 0487G.a G8.2.113
"""
AArch32 System register MPIDR bits [31:0] are architecturally mapped to
AArch64 System register MPIDR_EL1[31:0].
"""
Peeking at some armv7 doc and arm/kernel/topology.c the layout really looks
just the same, i.e. for both of them, with your example of:
core0: 0000000080000000
core1: 0000000080000100
core2: 0000000080000200
...
we'll get:
| | aff2 | aff1 | aff0 |
|-------+------+------+------|
| Core0 | 0 | 0 | 0 |
| Core1 | 0 | 1 | 0 |
| Core2 | 0 | 2 | 0 |
...
Now, arm64 doesn't fallback to MPIDR for topology information anymore since
3102bc0e6ac7 ("arm64: topology: Stop using MPIDR for topology information")
so without DT we would get:
| | package_id | core_id |
|-------+------------+---------|
| Core0 | 0 | 0 |
| Core1 | 0 | 1 |
| Core2 | 0 | 2 |
Whereas with an arm kernel we'll end up parsing MPIDR as:
| | package_id | core_id |
|-------+------------+---------|
| Core0 | 0 | 0 |
| Core1 | 1 | 0 |
| Core2 | 2 | 0 |
Did I get this right? Is this what you're observing?
> In addition, I think arm should also allow customers to configure cpu
> topologies via DT.
next prev parent reply other threads:[~2021-04-12 15:33 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-12 7:08 [PATCH 1/1] arm: topology: parse the topology from the dt Ruifeng Zhang
2021-04-12 11:31 ` Valentin Schneider
2021-04-12 12:20 ` Ruifeng Zhang
2021-04-12 12:40 ` Dietmar Eggemann
2021-04-13 6:18 ` Ruifeng Zhang
2021-04-12 15:32 ` Valentin Schneider [this message]
2021-04-13 6:13 ` Ruifeng Zhang
2021-04-13 11:40 ` Valentin Schneider
2021-04-13 13:26 ` Ruifeng Zhang
2021-04-14 9:42 ` Dietmar Eggemann
2021-04-14 11:26 ` Ruifeng Zhang
2021-04-14 13:53 ` Dietmar Eggemann
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87tuobmsba.mognet@arm.com \
--to=valentin.schneider@arm.com \
--cc=a.p.zijlstra@chello.nl \
--cc=dietmar.eggemann@arm.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=mingo@kernel.org \
--cc=nianfu.bai@unisoc.com \
--cc=rafael@kernel.org \
--cc=ruifeng.zhang0110@gmail.com \
--cc=ruifeng.zhang1@unisoc.com \
--cc=sudeep.holla@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).