[OpenWrt-Devel] [PATCH] ath79: switch to kernel 5.4

[Petr Štetiar]

Hauke Mehrtens <hauke at hauke-m.de> [2020-06-29 00:29:22]:

Hi,

> This is set in the configure_status() function:
> https://elixir.bootlin.com/linux/v5.4.47/source/arch/mips/kernel/traps.c#L2125
> But I think this is not working correctly under some unknown conditions.
> 
> I printed the read_c0_status() in the do_dsp() function and when this
> exception occurs the DSPEn bit is *not* set.

maybe it's due to the following:

 if (cpu_has_dsp)
 	status_set |= ST0_MX;

> Does someone see a bug in the broken version?

No.

> In this line:
>   4c:   40826000        mtc0    v0,c0_status
> in v0 the following bits should be set:

Seems to be alright:

> #define ST0_MX			0x01000000

 2c:   3c040100        lui     a0,0x100 << 16 = 0x01000000

> #define ST0_CU0			0x10000000

 8:   3c051000        lui     a1,0x1000 << 16 = 0x10000000

I think, that the problem is here, as the ST0_MX bit is set conditionally:

 20:   30630010        andi    v1,v1,0x10
 24:   10600003        beqz    v1,34 <configure_status+0x34>

 if (cpu_data[0].ases & 0x10) 	// 0x10 = MIPS_ASE_DSP

  #define MIPS_ASE_DSP           0x00000010
  #define cpu_has_dsp            __ase(MIPS_ASE_DSP)
  #define __ase(ase)             (cpu_data[0].ases & (ase))

and then status_set doesn't have ST0_MX bit set? Just printk the status_set.

-- ynezz