Re: [PATCH v3] MIPS: add support for buggy MT7621S core detection

Greg Ungerer
2021-09-16T02:56:45Z

Hi Ilya,

> Most MT7621 SoCs have 2 cores, which is detected and supported properly
> by CPS.
>
> Unfortunately, MT7621 SoC has a less common S variant with only one core.
> On MT7621S, GCR_CONFIG still reports 2 cores, which leads to hangs when
> starting SMP. CPULAUNCH registers can be used in that case to detect the
> absence of the second core and override the GCR_CONFIG PCORES field.
>
> Rework a long-standing OpenWrt patch to override the value of
> mips_cps_numcores on single-core MT7621 systems.
>
> Tested on a dual-core MT7621 device (Ubiquiti ER-X) and a single-core
> MT7621 device (Netgear R6220).

This is breaking core detection on my MT7621 based platforms.
I only get 2 cores detected now running 5.13. Reverting this change gives
me 4 cores back.

From a fully working (pre-change) system I get:

# cat /proc/cpuinfo
system type : MediaTek MT7621 ver:1 eco:3
machine : Digi EX15
processor : 0
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
shadow register sets : 1
kscratch registers : 0
package : 0
core : 0
VPE : 0
VCED exceptions : not available
VCEI exceptions : not available

processor : 1
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
shadow register sets : 1
kscratch registers : 0
package : 0
core : 0
VPE : 1
VCED exceptions : not available
VCEI exceptions : not available

processor : 2
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
shadow register sets : 1
kscratch registers : 0
package : 0
core : 1
VPE : 0
VCED exceptions : not available
VCEI exceptions : not available

processor : 3
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
shadow register sets : 1
kscratch registers : 0
package : 0
core : 1
VPE : 1
VCED exceptions : not available
VCEI exceptions : not available

After this patch is applied:

# cat /proc/cpuinfo
system type : MediaTek MT7621 ver:1 eco:3
machine : Digi EX15
processor : 0
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
shadow register sets : 1
kscratch registers : 0
package : 0
core : 0
VPE : 0
VCED exceptions : not available
VCEI exceptions : not available

processor : 1
cpu model : MIPS 1004Kc V2.15
BogoMIPS : 586.13
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa : mips1 mips2 mips32r1 mips32r2
ASEs implemented : mips16 dsp mt
shadow register sets : 1
kscratch registers : 0
package : 0
core : 0
VPE : 1
VCED exceptions : not available
VCEI exceptions : not available

Any ideas?

Regards
Greg

> Original 4.14 OpenWrt patch:
> Link: https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=4cdbc90a376dd0555201c1434a2081e055e9ceb7
> Current 5.10 OpenWrt patch:
> Link: https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/ramips/patches-5.10/320-mt7621-core-detect-hack.patch;h=c63f0f4c1ec742e24d8480e80553863744b58f6a;hb=10267e17299806f9885d086147878f6c492cb904
>
> Suggested-by: Felix Fietkau <nbd@nbd.name>
> Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
> ---
> arch/mips/include/asm/mips-cps.h | 23 ++++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/include/asm/mips-cps.h b/arch/mips/include/asm/mips-cps.h
> index fd43d876892e..35fb8ee6dd33 100644
> --- a/arch/mips/include/asm/mips-cps.h
> +++ b/arch/mips/include/asm/mips-cps.h
> @@ -10,6 +10,8 @@
> #include <linux/io.h>
> #include <linux/types.h>
>
> +#include <asm/mips-boards/launch.h>
> +
> extern unsigned long __cps_access_bad_size(void)
> __compiletime_error("Bad size for CPS accessor");
>
> @@ -165,11 +167,30 @@ static inline uint64_t mips_cps_cluster_config(unsigned int cluster)
> */
> static inline unsigned int mips_cps_numcores(unsigned int cluster)
> {
> + unsigned int ncores;
> +
> if (!mips_cm_present())
> return 0;
>
> /* Add one before masking to handle 0xff indicating no cores */
> - return (mips_cps_cluster_config(cluster) + 1) & CM_GCR_CONFIG_PCORES;
> + ncores = (mips_cps_cluster_config(cluster) + 1) & CM_GCR_CONFIG_PCORES;
> +
> + if (IS_ENABLED(CONFIG_SOC_MT7621)) {
> + struct cpulaunch *launch;
> +
> + /*
> + * Ralink MT7621S SoC is single core, but the GCR_CONFIG method
> + * always reports 2 cores. Check the second core's LAUNCH_FREADY
> + * flag to detect if the second core is missing. This method
> + * only works before the core has been started.
> + */
> + launch = (struct cpulaunch *)CKSEG0ADDR(CPULAUNCH);
> + launch += 2; /* MT7621 has 2 VPEs per core */
> + if (!(launch->flags & LAUNCH_FREADY))
> + ncores = 1;
> + }
> +
> + return ncores;
> }
>
> /**
> --
> 2.31.1