1. 14 Mar, 2021 1 commit
    • Huang Pei's avatar
      MIPS: clean up CONFIG_MIPS_PGD_C0_CONTEXT handling · c6972fb9
      Huang Pei authored
      +. LOONGSON64 use 0x98xx_xxxx_xxxx_xxxx as xphys cached, instread of
      0xa8xx_xxxx_xxxx_xxxx
      
      +. let CONFIG_MIPS_PGD_C0_CONTEXT depend on 64bit
      
      +. cast CAC_BASE into u64 to silence warning on MIPS32
      
      CP0 Context has enough room for wraping pgd into its 41-bit PTEBase field.
      
      +. For XPHYS, the trick is that pgd is 4kB aligned, and the PABITS <= 53,
      only save 53 - 12 = 41 bits, aka :
      
         bit[63:59] | 0000 00 |  bit[53:12] | 0000 0000 0000
      
      +. for CKSEG0, only save 29 - 12 = 17 bits
      
      when switching pgd, only need to save bit[53:12] or bit[28:12] into
      CP0 Context's bit[63:23], see folling asm generated at run time
      
      tlbmiss_handler_setup_pgd:
      	.set	push
      	.set	noreorder
      
      	dsra	a2, a0, 29
      	move	a3, a0
      	dins	a0, zero, 29, 35
      	daddiu	a2, a2, 4	//for CKSEG0, a2 from 0xfffffffffffffffc
      				//into 0
      
      	movn	a0, a3, a2
      	dsll	a0, a0, 11
      	jr	ra
      	dmtc0	a0, CP0_CONTEXT
      
      	.set	pop
      
      when using it on page walking
      
      	dmfc0	k0, CP0_CONTEXT
      	dins	k0, zero, 0, 23	         // zero badv2
      	ori	k0, k0, (CAC_BASE >> 53) // *prefix* with bit[63:59]
      	drotr	k0, k0, 11		 // kick it in the right place
      Signed-off-by: default avatarHuang Pei <huangpei@loongson.cn>
      Signed-off-by: default avatarThomas Bogendoerfer <tsbogend@alpha.franken.de>
      c6972fb9
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