> In my previous reply I said that "it is not so much as a need as it is a
> potential simplification." After further reflection, I don't think that
> is completely true. As we get into AMP systems with higher core counts,
> then implementing this functionality using the existing
> "protected-sources" implementation versus the new "pic-no-reset" work is
> going to be harder to maintain.
I'm not arguing that your approach isn't more suitable for AMP systems,
I just want to leave the existing protected-sources mechanism alone. I'm
not opposing adding a new, better, mechanism for newer platforms.
However, I'd name it differently. "pic-no-reset" doesn't carry enough
meaning in that case. What we want to point out here is that the PIC
has been pre-initialized.
Another option, which may be cleaner, is to stick to "no-reset" (no need
for pic- prefix) and make it do just that (prevent the reset), and then
use a positive variant of "protected-sources", call it
"allowed-sources". Maybe even make it a series of ranges. Then have the
MPIC only access these.
I think this is more robust as it would also prevent "accidental" use of
the wrong sources (bad device-tree, drivers that let you muck around
with irq numbers, etc...).
Cheers,
Ben.
> The reason being that *every* OS instance has to know about *every*
> other OSes interrupt sources, which is a little gross. You can see this
> happening already in "arch/powerpc/boot/dts/p2020rdb_camp_core0.dts" and
> "arch/powerpc/boot/dts/p2020rdb_camp_core1.dts":
>
> // p2020rdb_camp_core0.dts
> mpic: pic@40000 {
> ...
> // Sources used by the OS on core 1
> protected-sources = <
> 42 76 77 78 79 /* serial1 , dma2 */
> 29 30 34 26 /* enet0, pci1 */
> 0xe0 0xe1 0xe2 0xe3 /* msi */
> 0xe4 0xe5 0xe6 0xe7
> >;
> };
>
> // p2020rdb_camp_core1.dts
> mpic: pic@40000 {
> ...
> // Sources used by the OS on core 0
> protected-sources = <
> 17 18 43 42 59 47 /*ecm, mem, i2c, serial0, spi,gpio */
> 16 20 21 22 23 28 /* L2, dma1, USB */
> 03 35 36 40 31 32 33 /* mdio, enet1, enet2 */
> 72 45 58 25 /* sdhci, crypto , pci */
> >;
> };
>
> It is going to be a real pain to keep all of the lists up to date.
> Especially considering we already have sufficient information in the
> device tree to do this work. I do understand the concern of
> finding/testing the older systems. However, is the testing of those
> systems enough to keep out the proposed change and potentially lower
> maintenance in the future? Is the legacy system argument the only
> reason to keep this change out or are there other technical deficiencies?
>
> Also, in the proposed MPIC modifications there is a check for protected
> sources (it is treated as an alias for "pic-no-reset"; see PATCH 3 in
> the set) that should provide functionality equivalent to what systems
> using "protected-sources" already have. That check only looks for the
> presence of "protected-sources" and does not process the cells. Another
> option would be to leave in the protected sources implementation (but
> undocumented in the binding) and have the full "pic-no-reset" behavior
> there as well (and documented in the binding).
>
> If this has no chance of acceptance (?), then I will just re-submit the
> binding and implementation with "protected-sources" and the limited form
> of "pic-no-reset".
>
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
