On Thu, Mar 17, 2016 at 09:08:09PM +0000, Qais Yousef wrote:
> Malta defconfig compiles with GIC on. Hence when compiling for SMP it causes
> the
> new IPI code to be activated. But on qemu malta there's no GIC causing a
> BUG_ON(!ipidomain) to be hit in mips_smp_ipi_init().
>
> Since in that configuration one can only run a single core SMP (!), skip IPI
> initialisation if we detect that this is the case. It is a sensible behaviour
> to introduce and should keep such possible configuration to run rather than
> die
> hard unnecessarily.
Hi Qais/Ralf,
This patch is insufficient I'm afraid. It's entirely possible to use SMP
with multiple VPEs in a single core on Malta boards that don't have a
GIC - we have code handling IPIs in that case guarded by #ifdef
CONFIG_MIPS_MT_SMP in arch/mips/mti-malta/malta-int.c. I think the
BUG_ON needs to be removed entirely, unless that single-core multi-VPE
IPI code is also converted to use an IPI irqdomain.
Thanks,
Paul
>
> Signed-off-by: Qais Yousef <qsyou...@gmail.com>
> Reported-by: Guenter Roeck <li...@roeck-us.net>
> Cc: Guenter Roeck <li...@roeck-us.net>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: linux-m...@linux-mips.org
> Cc: linux-kernel@vger.kernel.org
> ---
> arch/mips/kernel/smp.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
> index 37708d9..27cb638 100644
> --- a/arch/mips/kernel/smp.c
> +++ b/arch/mips/kernel/smp.c
> @@ -243,6 +243,18 @@ static int __init mips_smp_ipi_init(void)
> struct irq_domain *ipidomain;
> struct device_node *node;
>
> + /*
> + * In some cases like qemu-malta, it is desired to try SMP with
> + * a single core. Qemu-malta has no GIC, so an attempt to set any IPIs
> + * would cause a BUG_ON() to be triggered since there's no ipidomain.
> + *
> + * Since for a single core system IPIs aren't required really, skip the
> + * initialisation which should generally keep any such configurations
> + * happy and only fail hard when trying to truely run SMP.
> + */
> + if (cpumask_weight(cpu_possible_mask) == 1)
> + return 0;
> +
> node = of_irq_find_parent(of_root);
> ipidomain = irq_find_matching_host(node, DOMAIN_BUS_IPI);
>
> --
> 2.7.3
>
>
