LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Alexander Graf <agraf@suse.de>
To: Rob Herring <robh@kernel.org>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Grant Likely <grant.likely@arm.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Mark Brown <broonie@kernel.org>, Stephen Boyd <sboyd@kernel.org>,
	boot-architecture@lists.linaro.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH] driver core: make deferring probe forever optional
Date: Wed, 2 May 2018 15:16:16 +0200	[thread overview]
Message-ID: <e7755330-bb6f-ad3a-fb82-7fc85a4cfac3@suse.de> (raw)
In-Reply-To: <20180501213114.20183-1-robh@kernel.org>

On 05/01/2018 11:31 PM, Rob Herring wrote:
> Deferred probe will currently wait forever on dependent devices to probe,
> but sometimes a driver will never exist. It's also not always critical for
> a driver to exist. Platforms can rely on default configuration from the
> bootloader or reset defaults for things such as pinctrl and power domains.
> This is often the case with initial platform support until various drivers
> get enabled. There's at least 2 scenarios where deferred probe can render
> a platform broken. Both involve using a DT which has more devices and
> dependencies than the kernel supports. The 1st case is a driver may be
> disabled in the kernel config. The 2nd case is the kernel version may
> simply not have the dependent driver. This can happen if using a newer DT
> (provided by firmware perhaps) with a stable kernel version.
>
> Unfortunately, this change breaks with modules as we have no way of
> knowing when modules are done loading. One possibility is to make this
> opt in or out based on compatible strings rather than at a subsystem level.
> Ideally this information could be extracted automatically somehow. OTOH,
> maybe the lists are pretty small. There's only a handful of subsystems
> that can be optional, and then only so many drivers in those that can be
> modules (at least for pinctrl, many drivers are built-in only).
>
> Cc: Alexander Graf <agraf@suse.de>
> Signed-off-by: Rob Herring <robh@kernel.org>
> ---
> This patch came out of a discussion on the ARM boot-architecture
> list[1] about DT forwards and backwards compatibility issues. There are
> issues with newer DTs breaking on older, stable kernels. Some of these
> are difficult to solve, but cases of optional devices not having
> kernel support should be solvable.

I think this is a reasonable approach. Maybe this should be a CONFIG 
option that disallows pinctrl drivers (and power domain later) to be =m? 
Then by default we could force those drivers to be compiled in, but if 
you really wanted to do kernel modules for pinctrl/pd you'd consciously 
potentially lose forward compatibility.


Alex

  parent reply	other threads:[~2018-05-02 13:16 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-01 21:31 Rob Herring
2018-05-01 22:08 ` Greg Kroah-Hartman
2018-05-02 11:40 ` Robin Murphy
2018-05-02 14:48   ` Rob Herring
2018-05-02 18:49     ` Robin Murphy
2018-05-05  1:25       ` Mark Brown
2018-05-07 13:37         ` Rob Herring
2018-05-02 13:16 ` Alexander Graf [this message]
2018-05-07 18:31 ` Bjorn Andersson
2018-05-07 19:55   ` Rob Herring
2018-05-07 22:34     ` Bjorn Andersson
2018-05-09  9:18       ` Mark Brown
2018-05-09  9:57       ` Alexander Graf
2018-05-09  9:44   ` Alexander Graf
2018-05-13 22:01     ` Linus Walleij
2018-05-14  7:37       ` Alexander Graf
2018-05-14 12:44         ` Michal Simek
2018-05-16 14:38           ` Linus Walleij

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=e7755330-bb6f-ad3a-fb82-7fc85a4cfac3@suse.de \
    --to=agraf@suse.de \
    --cc=boot-architecture@lists.linaro.org \
    --cc=broonie@kernel.org \
    --cc=devicetree@vger.kernel.org \
    --cc=grant.likely@arm.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=linus.walleij@linaro.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=robh@kernel.org \
    --cc=sboyd@kernel.org \
    --subject='Re: [RFC PATCH] driver core: make deferring probe forever optional' \
    /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

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).