• Xiaojie Yuan's avatar
    drm/amdgpu: add dummy read for some GCVM status registers · 53499173
    Xiaojie Yuan authored
    The GRBM register interface is now capable of bursting 1 cycle per
    register wr->wr, wr->rd much faster than previous muticycle per
    transaction done interface.  This has caused a problem where status
    registers requiring HW to update have a 1 cycle delay, due to the
    register update having to go through GRBM.
    
    SW may operate on an incorrect value if they write a register and
    immediately check the corresponding status register.
    
    Registers requiring HW to clear or set fields may be delayed by 1 cycle.
    For example,
    
    1. write VM_INVALIDATE_ENG0_REQ mask = 5a
    2. read VM_INVALIDATE_ENG0_ACK till the ack is same as the request mask = 5a
        a. HW will reset VM_INVALIDATE_ENG0_ACK = 0 until invalidation is complete
    3. write VM_INVALIDATE_ENG0_REQ mask = 5a
    4. read VM_INVALIDATE_ENG0_ACK till the ack is same as the request mask = 5a
        a. First read of VM_INVALIDATE_ENG0_ACK = 5a instead of 0
        b. Second read of VM_INVALIDATE_ENG0_ACK = 0 because
           the remote GRBM h/w register takes one extra cycle to be cleared
        c. In this case, SW will see a false ACK if they exit on first read
    
    Affected registers (only GC variant)  |  Recommended Dummy Read
    --------------------------------------+----------------------------
    VM_INVALIDATE_ENG*_ACK                |  VM_INVALIDATE_ENG*_REQ
    VM_L2_STATUS                          |  VM_L2_STATUS
    VM_L2_PROTECTION_FAULT_STATUS         |  VM_L2_PROTECTION_FAULT_STATUS
    VM_L2_PROTECTION_FAULT_ADDR_HI/LO32   |  VM_L2_PROTECTION_FAULT_ADDR_HI/LO32
    VM_L2_IH_LOG_BUSY                     |  VM_L2_IH_LOG_BUSY
    MC_VM_L2_PERFCOUNTER_HI/LO            |  MC_VM_L2_PERFCOUNTER_HI/LO
    ATC_L2_PERFCOUNTER_HI/LO              |  ATC_L2_PERFCOUNTER_HI/LO
    ATC_L2_PERFCOUNTER2_HI/LO             |  ATC_L2_PERFCOUNTER2_HI/LO
    Signed-off-by: default avatarXiaojie Yuan <xiaojie.yuan@amd.com>
    Reviewed-by: default avatarJack Xiao <Jack.Xiao@amd.com>
    Signed-off-by: default avatarAlex Deucher <alexander.deucher@amd.com>
    53499173
gmc_v10_0.c 24.5 KB