public inbox for linux-arm-kernel@lists.infradead.org
 help / color / mirror / Atom feed
From: Joonwon Kang <joonwonkang@google.com>
To: will@kernel.org, robin.murphy@arm.com, jpb@kernel.org
Cc: joro@8bytes.org, jgg@ziepe.ca, baolu.lu@linux.intel.com,
	 linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev,
	 linux-kernel@vger.kernel.org, stimim@google.com,
	cychu@google.com,  hhchung@google.com
Subject: [QUESTION] Is the ARM SMMU v3 implementation designed to always ignore SSID when SSID_VALID == 0?
Date: Tue, 28 Apr 2026 07:38:59 +0000	[thread overview]
Message-ID: <20260428073859.1502047-1-joonwonkang@google.com> (raw)

Hi team,

According to the ARM SMMU v3 spec, I believe that SSID should always be
ignored when SSID_VALID == 0 and the current ARM SMMU v3 module
implementation in the kernel seems to comply with this without exception.
For example, when handling an event from SMMU, the implementation checks
SSID_VALID(SSV) first and ignores SSID accordingly. If there is any
exception to this rule, I believe it is a bug.

Is it true for all the current and future cases? In other words, is it
**mandatory** that the ARM SMMU v3 implementation ignores SSID when
SSID_VALID == 0? or there might be some cases where the implementation
needs to refer to SSID even when SSID_VALID == 0?

Asking this question since our HW may not be able to clear SSID when
SSID_VALID == 0 and so there might be some garbage value in SSID at some
point of time(the HW will have a correct SSID when SSID_VALID == 1,
though). If the ARM SMMU v3 implementation is to refer to that garbage
value for any reason, the result would be devastating.

Thanks,
Joonwon Kang


             reply	other threads:[~2026-04-28  7:39 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-04-28  7:38 Joonwon Kang [this message]
2026-04-28  9:05 ` [QUESTION] Is the ARM SMMU v3 implementation designed to always ignore SSID when SSID_VALID == 0? Jean-Philippe Brucker
2026-04-28 11:14   ` Joonwon Kang
2026-04-28 12:15     ` Robin Murphy
2026-04-28 12:51       ` Joonwon Kang

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=20260428073859.1502047-1-joonwonkang@google.com \
    --to=joonwonkang@google.com \
    --cc=baolu.lu@linux.intel.com \
    --cc=cychu@google.com \
    --cc=hhchung@google.com \
    --cc=iommu@lists.linux.dev \
    --cc=jgg@ziepe.ca \
    --cc=joro@8bytes.org \
    --cc=jpb@kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=robin.murphy@arm.com \
    --cc=stimim@google.com \
    --cc=will@kernel.org \
    /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