arch/arm/common/mcpm_head.S

   1 /*
   2  * arch/arm/common/mcpm_head.S -- kernel entry point for multi-cluster PM
   3  *
   4  * Created by:  Nicolas Pitre, March 2012
   5  * Copyright:   (C) 2012-2013  Linaro Limited
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  *
  12  * Refer to Documentation/arm/cluster-pm-race-avoidance.txt
  13  * for details of the synchronisation algorithms used here.
  14  */
  15
  16 #include <linux/linkage.h>
  17 #include <asm/mcpm.h>
  18
  19 .if MCPM_SYNC_CLUSTER_CPUS
  20 .error "cpus must be the first member of struct mcpm_sync_struct"
  21 .endif
  22
  23         .macro  pr_dbg  string
  24 #if defined(CONFIG_DEBUG_LL) && defined(DEBUG)
  25         b       1901f
  26 1902:   .asciz  "CPU"
  27 1903:   .asciz  " cluster"
  28 1904:   .asciz  ": \string"
  29         .align
  30 1901:   adr     r0, 1902b
  31         bl      printascii
  32         mov     r0, r9
  33         bl      printhex8
  34         adr     r0, 1903b
  35         bl      printascii
  36         mov     r0, r10
  37         bl      printhex8
  38         adr     r0, 1904b
  39         bl      printascii
  40 #endif
  41         .endm
  42
  43         .arm
  44         .align
  45
  46 ENTRY(mcpm_entry_point)
  47
  48  THUMB( adr     r12, BSYM(1f)   )
  49  THUMB( bx      r12             )
  50  THUMB( .thumb                  )
  51 1:
  52         mrc     p15, 0, r0, c0, c0, 5           @ MPIDR
  53         ubfx    r9, r0, #0, #8                  @ r9 = cpu
  54         ubfx    r10, r0, #8, #8                 @ r10 = cluster
  55         mov     r3, #MAX_CPUS_PER_CLUSTER
  56         mla     r4, r3, r10, r9                 @ r4 = canonical CPU index
  57         cmp     r4, #(MAX_CPUS_PER_CLUSTER * MAX_NR_CLUSTERS)
  58         blo     2f
  59
  60         /* We didn't expect this CPU.  Try to cheaply make it quiet. */
  61 1:      wfi
  62         wfe
  63         b       1b
  64
  65 2:      pr_dbg  "kernel mcpm_entry_point\n"
  66
  67         /*
  68          * MMU is off so we need to get to various variables in a
  69          * position independent way.
  70          */
  71         adr     r5, 3f
  72         ldmia   r5, {r6, r7, r8}
  73         add     r6, r5, r6                      @ r6 = mcpm_entry_vectors
  74         ldr     r7, [r5, r7]                    @ r7 = mcpm_power_up_setup_phys
  75         add     r8, r5, r8                      @ r8 = mcpm_sync
  76
  77         mov     r0, #MCPM_SYNC_CLUSTER_SIZE
  78         mla     r8, r0, r10, r8                 @ r8 = sync cluster base
  79
  80         @ Signal that this CPU is coming UP:
  81         mov     r0, #CPU_COMING_UP
  82         mov     r5, #MCPM_SYNC_CPU_SIZE
  83         mla     r5, r9, r5, r8                  @ r5 = sync cpu address
  84         strb    r0, [r5]
  85
  86         @ At this point, the cluster cannot unexpectedly enter the GOING_DOWN
  87         @ state, because there is at least one active CPU (this CPU).
  88
  89         @ Note: the following is racy as another CPU might be testing
  90         @ the same flag at the same moment.  That'll be fixed later.
  91         ldrb    r0, [r8, #MCPM_SYNC_CLUSTER_CLUSTER]
  92         cmp     r0, #CLUSTER_UP                 @ cluster already up?
  93         bne     mcpm_setup                      @ if not, set up the cluster
  94
  95         @ Otherwise, skip setup:
  96         b       mcpm_setup_complete
  97
  98 mcpm_setup:
  99         @ Control dependency implies strb not observable before previous ldrb.
 100
 101         @ Signal that the cluster is being brought up:
 102         mov     r0, #INBOUND_COMING_UP
 103         strb    r0, [r8, #MCPM_SYNC_CLUSTER_INBOUND]
 104         dmb
 105
 106         @ Any CPU trying to take the cluster into CLUSTER_GOING_DOWN from this
 107         @ point onwards will observe INBOUND_COMING_UP and abort.
 108
 109         @ Wait for any previously-pending cluster teardown operations to abort
 110         @ or complete:
 111 mcpm_teardown_wait:
 112         ldrb    r0, [r8, #MCPM_SYNC_CLUSTER_CLUSTER]
 113         cmp     r0, #CLUSTER_GOING_DOWN
 114         bne     first_man_setup
 115         wfe
 116         b       mcpm_teardown_wait
 117
 118 first_man_setup:
 119         dmb
 120
 121         @ If the outbound gave up before teardown started, skip cluster setup:
 122
 123         cmp     r0, #CLUSTER_UP
 124         beq     mcpm_setup_leave
 125
 126         @ power_up_setup is now responsible for setting up the cluster:
 127
 128         cmp     r7, #0
 129         mov     r0, #1          @ second (cluster) affinity level
 130         blxne   r7              @ Call power_up_setup if defined
 131         dmb
 132
 133         mov     r0, #CLUSTER_UP
 134         strb    r0, [r8, #MCPM_SYNC_CLUSTER_CLUSTER]
 135         dmb
 136
 137 mcpm_setup_leave:
 138         @ Leave the cluster setup critical section:
 139
 140         mov     r0, #INBOUND_NOT_COMING_UP
 141         strb    r0, [r8, #MCPM_SYNC_CLUSTER_INBOUND]
 142         dsb
 143         sev
 144
 145 mcpm_setup_complete:
 146         @ If a platform-specific CPU setup hook is needed, it is
 147         @ called from here.
 148
 149         cmp     r7, #0
 150         mov     r0, #0          @ first (CPU) affinity level
 151         blxne   r7              @ Call power_up_setup if defined
 152         dmb
 153
 154         @ Mark the CPU as up:
 155
 156         mov     r0, #CPU_UP
 157         strb    r0, [r5]
 158
 159         @ Observability order of CPU_UP and opening of the gate does not matter.
 160
 161 mcpm_entry_gated:
 162         ldr     r5, [r6, r4, lsl #2]            @ r5 = CPU entry vector
 163         cmp     r5, #0
 164         wfeeq
 165         beq     mcpm_entry_gated
 166         dmb
 167
 168         pr_dbg  "released\n"
 169         bx      r5
 170
 171         .align  2
 172
 173 3:      .word   mcpm_entry_vectors - .
 174         .word   mcpm_power_up_setup_phys - 3b
 175         .word   mcpm_sync - 3b
 176
 177 ENDPROC(mcpm_entry_point)
 178
 179         .bss
 180         .align  5
 181
 182         .type   mcpm_entry_vectors, #object
 183 ENTRY(mcpm_entry_vectors)
 184         .space  4 * MAX_NR_CLUSTERS * MAX_CPUS_PER_CLUSTER
 185
 186         .type   mcpm_power_up_setup_phys, #object
 187 ENTRY(mcpm_power_up_setup_phys)
 188         .space  4               @ set by mcpm_sync_init()