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From: Zev Weiss <zweiss@equinix.com>
To: Jeremy Kerr <jk@codeconstruct.com.au>
Cc: Andrew Jeffery <andrew@aj.id.au>,
	"openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>,
	Eddie James <eajames@linux.ibm.com>
Subject: Re: [PATCH RFC] Specifying default-disabled devices
Date: Fri, 10 Sep 2021 05:28:36 +0000	[thread overview]
Message-ID: <20210910052835.GF17315@packtop> (raw)
In-Reply-To: <1df72fd584f9c54544f9d5fafcd6232e3079ee49.camel@codeconstruct.com.au>

On Thu, Sep 09, 2021 at 09:04:05PM PDT, Jeremy Kerr wrote:
>Hi Zev,
>
>> However, I think I may have spoken too soon regarding the relative
>> simplicity of implementing it -- from a quick glance at it, I think
>> I'd want to take of_device_is_available() and split it into some
>> variants for strictly-okay and okay-or-reserved (and similarly for
>> of_get_next_available_child()).  The problem there is that there are
>> currently circa 200 callers of those functions scattered thoughout the
>> tree, and auditing each of them individually to determine which of
>> those semantics is actually appropriate in each case seems...a bit
>> daunting.
>
>I think you should be OK, if you stage it this way:
>
> - add status = "reserved" to your device tree; this will supress the
>   automatic binding right away. With the current code, all it cares
>   about is status = "okay" (or "ok"), so you'll at least keep the
>   device quiesced.
>
>   with that, there won't be an easy way to initiate the driver probe,
>   but maybe that's OK for your use-case if you're doing the bind
>   manually.
>

From some grepping around it looks like the only check is for
"okay"/"ok", and nothing actually checks for "disabled", so I'd think
any non-OK string (including "reserved") would end up being equivalent
to "disabled", and hence result in the device node not being
instantiated at all.  (A quick test appears to confirm; with status =
"reserved", an attempt to bind via sysfs fails with ENODEV.)


Zev

  reply	other threads:[~2021-09-10  5:29 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10  2:24 Zev Weiss
2021-09-10  2:33 ` Jeremy Kerr
2021-09-10  3:49   ` Zev Weiss
2021-09-10  4:04     ` Jeremy Kerr
2021-09-10  5:28       ` Zev Weiss [this message]
2021-09-10  7:59         ` Jeremy Kerr
2021-09-10  8:35           ` Zev Weiss
2021-09-10  9:08             ` Jeremy Kerr
2021-09-10 21:59               ` Zev Weiss
2021-09-21  2:56                 ` Zev Weiss
2021-09-10  4:36 ` Oliver O'Halloran

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