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

Sergio Paracuellos
2021-09-30T13:35:28Z

Hi Greg,

On Thu, Sep 30, 2021 at 3:13 PM Greg Ungerer <gerg@kernel.org> wrote:
>
> Hi Steven,
>
> On 16/9/21 6:54 pm, Strontium wrote:
> > Hi Greg,
> >
> > I had trouble with this as well. This line from the patch:
> >
> >> if (!(launch->flags & LAUNCH_FREADY))
> >
> > is checking ram which I believe is supposed to be set by the bootloader.
> > On my platform it looked like the preloaded uboot wasn't setting that as
> > expected.
> > If you have control over your bootloader you can force this ram address
> > to be what the kernel wants, or you can do what i did, because i didn't
> > have that targets uboot src, and wedge before the kernel starts to force
> > the ram to the required state, like so:
>
> Well, my solution was to revert that patch locally :-)
>
> But many people will not have control of or the desire to change
> their u-boot loader. I would have figured this ends up being a
> real regression for many (most?) users of this SoC.

Agree.

>
>
> > #define CORE0_INITIAL_CPU_STATE (0xf00)
> > #define CORE_FL_OFFSET (0x1C)
> > #define FLAG_LAUNCH_FREADY (1)
> >
> > #define WRITEREG(r, v) *(volatile uint32_t *)(r) = v
> > #define KSEG1ADDR(_x) (((_x)&0x1fffffff) | 0xa0000000)
> >
> > void set_core(uint32_t core)
> > {
> > uint32_t start = CORE0_INITIAL_CPU_STATE + (0x40 * core);
> > WRITEREG(KSEG1ADDR(start + CORE_FL_OFFSET), FLAG_LAUNCH_FREADY);
> > }
> >
> > void fix_cores(void) {
> > // Fixes the flags for each core, just before running the kernel.
> > // Means we don't have to patch the kernel check for valid CPU's.
> > for (int i = 0; i < 4; i++) {
> > set_core(i);
> > }
> > }
> >
> > It seems that memory section is supposed to set all the cores registers
> > before the kernel runs, but i never found it did anything except that 1
> > flag.
> >
> > Obviously a better way would be to properly detect the number of cores
> > and not rely on the boot loader to set a flag in ram, I don't know if
> > that's even possible.
>
> I can't help but think this commit is not a proper fix for this problem.

I also do think this commit should be reverted. Ilya, do you have a
strong opinion to maintain it instead?

>
> Regards
> Greg

Best regards,
Sergio Paracuellos
>
>
> > Steven Johnson
> >
> > On 16/9/21 09:56, Greg Ungerer wrote:
> >> 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
> >>
> >