• Maciej W. Rozycki's avatar
    TC: Set DMA masks for devices · 3f2aa244
    Maciej W. Rozycki authored
    Fix a TURBOchannel support regression with commit 205e1b7f
    ("dma-mapping: warn when there is no coherent_dma_mask") that caused
    coherent DMA allocations to produce a warning such as:
    
    defxx: v1.11 2014/07/01  Lawrence V. Stefani and others
    tc1: DEFTA at MMIO addr = 0x1e900000, IRQ = 20, Hardware addr = 08-00-2b-a3-a3-29
    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 1 at ./include/linux/dma-mapping.h:516 dfx_dev_register+0x670/0x678
    Modules linked in:
    CPU: 0 PID: 1 Comm: swapper Not tainted 4.19.0-rc6 #2
    Stack : ffffffff8009ffc0 fffffffffffffec0 0000000000000000 ffffffff80647650
            0000000000000000 0000000000000000 ffffffff806f5f80 ffffffffffffffff
            0000000000000000 0000000000000000 0000000000000001 ffffffff8065d4e8
            98000000031b6300 ffffffff80563478 ffffffff805685b0 ffffffffffffffff
            0000000000000000 ffffffff805d6720 0000000000000204 ffffffff80388df8
            0000000000000000 0000000000000009 ffffffff8053efd0 ffffffff806657d0
            0000000000000000 ffffffff803177f8 0000000000000000 ffffffff806d0000
            9800000003078000 980000000307b9e0 000000001e900000 ffffffff80067940
            0000000000000000 ffffffff805d6720 0000000000000204 ffffffff80388df8
            ffffffff805176c0 ffffffff8004dc78 0000000000000000 ffffffff80067940
            ...
    Call Trace:
    [<ffffffff8004dc78>] show_stack+0xa0/0x130
    [<ffffffff80067940>] __warn+0x128/0x170
    ---[ end trace b1d1e094f67f3bb2 ]---
    
    This is because the TURBOchannel bus driver fails to set the coherent
    DMA mask for devices enumerated.
    
    Set the regular and coherent DMA masks for TURBOchannel devices then,
    observing that the bus protocol supports a 34-bit (16GiB) DMA address
    space, by interpreting the value presented in the address cycle across
    the 32 `ad' lines as a 32-bit word rather than byte address[1].  The
    architectural size of the TURBOchannel DMA address space exceeds the
    maximum amount of RAM any actual TURBOchannel system in existence may
    have, hence both masks are the same.
    
    This removes the warning shown above.
    
    References:
    
    [1] "TURBOchannel Hardware Specification", EK-369AA-OD-007B, Digital
        Equipment Corporation, January 1993, Section "DMA", pp. 1-15 -- 1-17
    Signed-off-by: 's avatarMaciej W. Rozycki <macro@linux-mips.org>
    Signed-off-by: 's avatarPaul Burton <paul.burton@mips.com>
    Patchwork: https://patchwork.linux-mips.org/patch/20835/
    Fixes: 205e1b7f ("dma-mapping: warn when there is no coherent_dma_mask")
    Cc: stable@vger.kernel.org # 4.16+
    Cc: Ralf Baechle <ralf@linux-mips.org>
    3f2aa244
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