• Eugeniy Paltsev's avatar
    ARC: dma [non-IOC] setup SMP_CACHE_BYTES and cache_line_size · eb277739
    Eugeniy Paltsev authored
    As for today we don't setup SMP_CACHE_BYTES and cache_line_size for
    ARC, so they are set to L1_CACHE_BYTES by default. L1 line length
    (L1_CACHE_BYTES) might be easily smaller than L2 line (which is
    usually the case BTW). This breaks code.
    
    For example this breaks ethernet infrastructure on HSDK/AXS103 boards
    with IOC disabled, involving manual cache flushes
    Functions which alloc and manage sk_buff packet data area rely on
    SMP_CACHE_BYTES define. In the result we can share last L2 cache
    line in sk_buff linear packet data area between DMA buffer and
    some useful data in other structure. So we can lose this data when
    we invalidate DMA buffer.
    
       sk_buff linear packet data area
                    |
                    |
                    |         skb->end        skb->tail
                    V            |                |
                                 V                V
    ----------------------------------------------.
          packet data            | <tail padding> |  <useful data in other struct>
    ----------------------------------------------.
    
    ---------------------.--------------------------------------------------.
         SLC line        |             SLC (L2 cache) line (128B)           |
    ---------------------.--------------------------------------------------.
            ^                                     ^
            |                                     |
         These cache lines will be invalidated when we invalidate skb
         linear packet data area before DMA transaction starting.
    
    This leads to issues painful to debug as it reproduces only if
    (sk_buff->end - sk_buff->tail) < SLC_LINE_SIZE and
    if we have some useful data right after sk_buff->end.
    
    Fix that by hardcode SMP_CACHE_BYTES to max line length we may have.
    Signed-off-by: default avatarEugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
    Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
    eb277739
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