• HyeonSeung Jang's avatar
    [POWERPC] spufs: fix context switch during page fault · 28347bce
    HyeonSeung Jang authored
    
    
    For better explanation, I break down the page fault handling into steps:
    
    1) There is a page fault caused by DMA operation initiated by SPU and
    DMA is suspended.
    
    2) The interrupt handler 'spu_irq_class_1()/__spu_trap_data_map()' is
    called and it just wakes up the sleeping spe-manager thread.
    
    3) by PPE scheduler, the corresponding bottom half,
    spu_irq_class_1_bottom() is called in process context and DMA is
    restarted.
    
    There can be a quite large time gap between 2) and 3) and I found
    the following problem:
    
    Between 2) and 3) If the context becomes unbound, 3) is not executed
    because when the spe-manager thread is awaken, the context is already
    saved. (This situation can happen, for example, when a high priority spe
    thread newly started in that time gap)
    
    But the actual problem is that the corresponding SPU context does not
    work even if it is bound again to a SPU.
    
    Besides I can see the following warning in mambo simulator when the
    context becomes
    unbound(in save_mfc_cmd()), i.e. when unbind() is called for the
    context after step 2) before 3) :
    
    'WARNING: 61392752237: SPE2: MFC_CMD_QUEUE channel count of 15 is
    inconsistent with number of available DMA queue entries of 16'
    
    After I go through available documents, I found that the problem is
    because the suspended DMA is not restarted when it is bound again.
    
    Signed-off-by: default avatarArnd Bergmann <arnd.bergmann@de.ibm.com>
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    28347bce