On 02/03/2011 09:56 AM, Arnd Bergmann wrote:
On Thursday 03 February 2011, Meador Inge wrote:
In a recent discussion [1, 2] concerning device trees for AMP systems, the
question of whether we really need 'protected-sources' arose. The general
consensus was that if you don't want a source to be used, then it should *not*
be mentioned in an 'interrupts' property. If a source really needs to be
mentioned, then it should be put in a property other than 'interrupts' with
a specific binding for that use case.
[1]
http://lists.ozlabs.org/pipermail/devicetree-discuss/2011-January/004038.html
[2]
http://lists.ozlabs.org/pipermail/devicetree-discuss/2011-January/003991.html
That doesn't work in the case that this code was written for:
http://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg01394.html
The problem is that you don't want the mpic to initialize the interrupt
line to the default, but instead leave it at whatever the boot firmware
has set up. Note that interrupt is not listed in any "interrupts"
property of any of the devices on the CPU interpreting the device
tree, but it may be mentioned in the device tree that another CPU
uses to access the same MPIC.
Arnd
We touched on that use case before on list. However, I did a really bad
job of explaining things in the above patch description. I understand
that the sources that are being protected are mentioned in a device tree
other than the one that actually interprets the 'protected-sources'
property.
The idea is to try and expand the meaning of the 'no-reset' property to
cover what 'protected-sources' was taking care of, but without
explicitly naming the sources.
In the protected sources version of the code, the relevant MPIC
initialization went something like (in 'mpic_init'):
for (i = 0; i < mpic->num_sources; i++) {
/* start with vector = source number, and masked */
u32 vecpri = MPIC_VECPRI_MASK | i |
(8 << MPIC_VECPRI_PRIORITY_SHIFT);
/* check if protected */
if (mpic->protected && test_bit(i, mpic->protected))
continue;
/* init hw */
mpic_irq_write(i, MPIC_INFO(IRQ_VECTOR_PRI), vecpri);
mpic_irq_write(i, MPIC_INFO(IRQ_DESTINATION), 1 << cpu);
}
So unless a particular source was marked as protected, it would get the
VECPRI and CPU binding initialization. This is the exact behavior that
you describe above, Arnd.
In the 'no-reset' model, the initialization looks more like (see PATCH 3
in the set for the full implementation):
if (mpic->flags & MPIC_WANTS_RESET) {
for (i = 0; i < mpic->num_sources; i++) {
mpic_init_vector(mpic, hw);
}
}
So in 'mpic_init' we don't initialize anything and then in
'mpic_host_map' we lazily do the VECPRI and CPU binding initialization with:
if (!(mpic->flags & MPIC_WANTS_RESET))
if (!(mpic_is_ipi(mpic, hw)
|| mpic_is_timer_interrupt(mpic, hw)))
mpic_init_vector(mpic, hw);
Thus when 'no-reset' is thrown it ensures that only the sources which
are mentioned in the device tree are actually initialized. The net
effect should be the same as what 'protected-sources' was accomplishing,
but without having to maintain the list of sources in the property cell.
--
Meador Inge | meador_inge AT mentor.com
Mentor Embedded | http://www.mentor.com/embedded-software
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