archive mirror
 help / color / mirror / Atom feed
From: Arnd Bergmann <>
To: "Clément Léger" <>
Cc: Lee Jones <>,
	Rob Herring <>, Mark Brown <>,
	Greg Kroah-Hartman <>,
	"Rafael J. Wysocki" <>,
	Arnd Bergmann <>, DTML <>,
	Linux Kernel Mailing List <>,
	Peng Fan <>, Sudeep Holla <>,
	Alexandre Belloni <>
Subject: Re: [PATCH 2/3] syscon: add support for "syscon-smc" compatible
Date: Fri, 23 Jul 2021 18:07:44 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, Jul 23, 2021 at 3:52 PM Clément Léger <> wrote:
> System controllers can be placed under secure monitor control when running
> under them. In order to keep existing code which accesses such system
> controllers using a syscon, add support for "syscon-smc" compatible.
> When enable, the syscon will handle this new compatible and look for an
> "arm,smc-id" property to execute the appropriate SMC. A SMC regmap is then
> created to forward register access to the secure monitor.
> Signed-off-by: Clément Léger <>

I don't see anything wrong with the implementation, but this worries
me conceptually, because of the ways this might get abused:

- this creates one more way to keep device drivers hidden away
  behind firmware when they should be in the kernel. You can already
  do that with separate SMC calls, but adding an indirection makes it
  sneakier. If the 'registers' in here are purely

- This may be seen as an easy way out for firmware writers that just
   expose a bare register-level interface when the correct solution would
   be to create a high-level interface.

There is also a problem with locking: In the case that both firmware and
kernel have to access registers within a syscon area, you may need to
have a semaphore to protect an atomic sequence of accesses, but since
the interface only provides a single register load/store, there is no way for
a kernel driver to serialize against a firmware-internal driver.


  parent reply	other threads:[~2021-07-23 16:08 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-23 13:52 [PATCH 0/3] add SMC based regmap driver for secure syscon access Clément Léger
2021-07-23 13:52 ` [PATCH 1/3] regmap: add regmap using ARM SMCCC Clément Léger
2021-07-23 14:43   ` Mark Brown
2021-07-23 15:53     ` Clément Léger
2021-07-23 16:37       ` Mark Brown
2021-07-23 13:52 ` [PATCH 2/3] syscon: add support for "syscon-smc" compatible Clément Léger
2021-07-23 15:27   ` Lee Jones
2021-07-23 15:56     ` Clément Léger
2021-07-23 16:07   ` Arnd Bergmann [this message]
2021-07-23 16:41     ` Mark Brown
2021-07-24 12:36     ` Peng Fan (OSS)
2021-07-24  7:00   ` kernel test robot
2021-07-23 13:52 ` [PATCH 3/3] dt-bindings: mfd: add "syscon-smc" YAML description Clément Léger
2021-07-29 21:19   ` Rob Herring
2021-07-30  7:21     ` Clément Léger

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:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \ \

* 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).