Re: [PATCH v3 11/16] hw/arm/raspi: Use -smp cores=<N> option to restrict enabled cores

[Bonnans, Laurent]

On 10/20/19 1:47 AM, Philippe Mathieu-Daudé wrote:
> The abstract TYPE_BCM283X device provides a 'enabled-cpus' property
> to restrict the number of cores powered on reset. This because on
> real hardware the GPU is responsible of starting the cores and keep
> them spinning until the Linux kernel is ready to use them.
> When using the -kernel paramenter, QEMU does this by installing the
> 'raspi_smpboot' code when arm_boot_info::write_board_setup() is
> called. This is a special feature to help the Linux kernel, and can
> only be used with a Linux kernel.
>
> Even if loaded with the -kernel option, U-boot is not Linux, thus
> is not recognized as it and the raspi_smpboot code is not installed.
>
> Upon introduction of this machine in commit 1df7d1f9303, the -smp <N>
> option allowd to limit the number of cores powered on reset.
> Unfortunately later commit 72649619341 added a check which made this
> feature unusable:
>
>    $ qemu-system-aarch64 -M raspi3 -smp 1
>    qemu-system-aarch64: Invalid SMP CPUs 1. The min CPUs supported by machine 
> 'raspi3' is 4
>
> Fortunately, the -smp option allow various kind of CPU topology:
>
>    -smp 
> [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,dies=dies][,sockets=sockets]
>             set the number of CPUs to 'n' [default=1]
>             maxcpus= maximum number of total cpus, including
>             offline CPUs for hotplug, etc
>             cores= number of CPU cores on one socket (for PC, it's on one die)
>             threads= number of threads on one CPU core
>             dies= number of CPU dies on one socket (for PC only)
>             sockets= number of discrete sockets in the system
>
> Let's use the 'cores' argument to specify the number of cores powered
> at reset to restore this feature, and allow to boot U-boot.
>
> We can now run U-boot using:
>
>    $ qemu-system-aarch64 -M raspi3 -smp 4,cores=1 ...
>
> Reported-by: Laurent Bonnans <address@hidden>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>   hw/arm/raspi.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/arm/raspi.c b/hw/arm/raspi.c
> index 569d85c11a..45d3f91f95 100644
> --- a/hw/arm/raspi.c
> +++ b/hw/arm/raspi.c
> @@ -190,8 +190,8 @@ static void raspi_init(MachineState *machine, int version)
>       /* Setup the SOC */
>       object_property_add_const_link(OBJECT(&s->soc), "ram", OBJECT(&s->ram),
>                                      &error_abort);
> -    object_property_set_int(OBJECT(&s->soc), machine->smp.cpus, 
> "enabled-cpus",
> -                            &error_abort);
> +    object_property_set_int(OBJECT(&s->soc), machine->smp.cores,
> +                            "enabled-cpus", &error_abort);
>       int board_rev = version == 3 ? 0xa02082 : 0xa21041;
>       object_property_set_int(OBJECT(&s->soc), board_rev, "board-rev",
>                               &error_abort);

Hi Phil,

Thanks for the patch, I finally got the chance to make some tests (sorry 
about the delay).

Using the proposed -smp options indeed helps to run u-boot elfs 
directly. However, the cores fail to start when switching to linux 
(tested on raspi2):

[ 0.071030] smp: Bringing up secondary CPUs ...
[ 1.157876] CPU1: failed to come online
[ 2.219899] CPU2: failed to come online
[ 3.285412] CPU3: failed to come online
[ 3.286137] smp: Brought up 1 node, 1 CPU
[ 3.286766] SMP: Total of 1 processors activated (125.00 BogoMIPS).
[ 3.287442] CPU: All CPU(s) started in SVC mode.

The behavior persist even without using the option on the command line.
The normal behavior is restored if I use "-smp 4, cores=4"

Greetings,

Laurent