Re: [PATCH 4/8] arm64: dts: add NXP S32G2 support

[Marc Zyngier]

On Fri, 20 Aug 2021 16:15:49 +0100,
Chester Lin <clin@xxxxxxxx> wrote:
> 
> On Fri, Aug 20, 2021 at 02:12:13PM +0100, Marc Zyngier wrote:
> > On Thu, 12 Aug 2021 18:26:28 +0100,
> > Andreas Färber <afaerber@xxxxxxx> wrote:
> > > 
> > > Hi Chester et al.,
> > > 
> > > On 05.08.21 08:54, Chester Lin wrote:
> > > > Add an initial dtsi file for generic SoC features of NXP S32G2.
> > > > 
> > > > Signed-off-by: Chester Lin <clin@xxxxxxxx>
> > > > ---
> > > >  arch/arm64/boot/dts/freescale/s32g2.dtsi | 98 ++++++++++++++++++++++++
> > > >  1 file changed, 98 insertions(+)
> > > >  create mode 100644 arch/arm64/boot/dts/freescale/s32g2.dtsi
> > > > 
> > > > diff --git a/arch/arm64/boot/dts/freescale/s32g2.dtsi b/arch/arm64/boot/dts/freescale/s32g2.dtsi
> > > > new file mode 100644
> > > > index 000000000000..3321819c1a2d
> > > > --- /dev/null
> > > > +++ b/arch/arm64/boot/dts/freescale/s32g2.dtsi
> > 
> > [...]
> > 
> > > > +		gic: interrupt-controller@50800000 {
> > > > +			compatible = "arm,gic-v3";
> > > > +			#interrupt-cells = <3>;
> > > > +			interrupt-controller;
> > > > +			reg = <0 0x50800000 0 0x10000>,
> > > > +			      <0 0x50880000 0 0x200000>,
> > 
> > That's enough redistributor space for 16 CPUs. However, you only
> > describe 4. Either the number of CPUs is wrong, the size is wrong, or
> > the GIC has been configured for more cores than the SoC has.
> 
> Confirmed the SoC can only find 4 redistributors:
> 
> localhost:~ # dmesg | grep CPU
> [    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034]
> [    0.000000] Detected VIPT I-cache on CPU0
> [    0.000000] CPU features: detected: GIC system register CPU interface
> [    0.000000] CPU features: detected: ARM erratum 845719
> [    0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
> [    0.000000] rcu:     RCU restricting CPUs from NR_CPUS=480 to nr_cpu_ids=4.
> [    0.000000] GICv3: CPU0: found redistributor 0 region 0:0x0000000050880000
> [    0.063865] smp: Bringing up secondary CPUs ...
> [    0.068852] Detected VIPT I-cache on CPU1
> [    0.068894] GICv3: CPU1: found redistributor 1 region 0:0x00000000508a0000
> [    0.068963] CPU1: Booted secondary processor 0x0000000001 [0x410fd034]
> [    0.069809] Detected VIPT I-cache on CPU2
> [    0.069851] GICv3: CPU2: found redistributor 100 region 0:0x00000000508c0000
> [    0.069903] CPU2: Booted secondary processor 0x0000000100 [0x410fd034]
> [    0.070698] Detected VIPT I-cache on CPU3
> [    0.070722] GICv3: CPU3: found redistributor 101 region 0:0x00000000508e0000
> [    0.070749] CPU3: Booted secondary processor 0x0000000101 [0x410fd034]
> [    0.070847] smp: Brought up 1 node, 4 CPUs
> <..snip..>

That's not the correct way to find out. Each CPU tries to find its
matching RD in the region. This doesn't mean there aren't more RDs
present in the GIC.

You need to iterate over all the RDs in the region until you find one
that has GICR_TYPER.Last == 1. This will give you the actual count.
Alternatively, you can check whether the RD at 508e0000 has that bit
set. If it doesn't, then you know there are more RDs than CPUs.

	M.

-- 
Without deviation from the norm, progress is not possible.