Re: [PATCH 10/14] irqchip/mips-gic: Add a IPI hierarchy domain

From: Qais Yousef
Date: Tue Nov 17 2015 - 05:08:39 EST

On 11/16/2015 05:17 PM, Thomas Gleixner wrote:
On Mon, 9 Nov 2015, Qais Yousef wrote:
On 11/07/2015 02:51 PM, Thomas Gleixner wrote:
Generally it's hard to know whether a real device is connected to a hwirq or
not. I am saving a patch where we get a set of free hwirqs from DT as only the
SoC designer knows what hwirq are actually free and safe to use for IPI. I'll
send this patch with the DT IPI changes or the rproc driver that I will be
send once these changes are merged.

The current code assumes that the last 2 * NR_CPUs hwirqs are always free to
use for Linux SMP.
So what you're saying is that you cannot rely on the last X hwirqs
being available for IPIs. That's insane and to my knowledge there is
no hardware out there which does not reserve a consecutive IPI space.

If I read the code you were suggesting correctly, you were trying to fit the IPIs in any available non allocated area in the GIC space. What I am trying to say is that we can only work on a limited subset of this space that we are told explicitly it's safe to use for IPIs. Most likely it's consecutive, but I don't feel brave enough to make this assumption personally - maybe I'm over paranoid.. I'm more keen on anything that would simplify this patch series now though.

I'll do my best with the next series but maybe we'd need to iterate this more than once till I get it right.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at