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From: Nathan Lynch <nathanl@linux.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 03/13] powerpc/rtas: avoid device tree lookups in
 rtas_os_term()
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Date: Tue, 29 Nov 2022 09:37:36 -0600
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"Nicholas Piggin" <npiggin@gmail.com> writes:
> On Tue Nov 29, 2022 at 4:26 AM AEST, Nathan Lynch wrote:
>> "Nicholas Piggin" <npiggin@gmail.com> writes:
>> > On Sat Nov 19, 2022 at 1:07 AM AEST, Nathan Lynch wrote:
>> >> rtas_os_term() is called during panic. Its behavior depends on a
>> >> couple of conditions in the /rtas node of the device tree, the
>> >> traversal of which entails locking and local IRQ state changes. If the
>> >> kernel panics while devtree_lock is held, rtas_os_term() as currently
>> >> written could hang.
>> >
>> > Nice.
>> >
>> >>
>> >> Instead of discovering the relevant characteristics at panic time,
>> >> cache them in file-static variables at boot. Note the lookup for
>> >> "ibm,extended-os-term" is converted to of_property_read_bool() since
>> >> it is a boolean property, not a RTAS function token.
>> >
>> > Small nit, but you could do that at the query site unless you
>> > were going to start using ibm,os-term without the extended
>> > capability.
>>
>> I'm unsure that this is what you're suggesting, but we don't want to use
>> of_property_read_bool() in this context either, because it has the same
>> undesirable qualities as rtas_token().
>
> I mean rtas_initialize() could do
>
> 	if (of_property_read_bool(rtas.dev, "ibm,extended-os-term"))
> 		ibm_os_term_token = rtas_token("ibm,os-term");

Oh of course, thanks. Since I need to do a v2 anyway, I'll make that
change.