• Thomas Gleixner's avatar
    ARM: common: edma: Fix xbar mapping · cf7eb979
    Thomas Gleixner authored
    This is another great example of trainwreck engineering:
    
    commit 2646a0e529 (ARM: edma: Add EDMA crossbar event mux support)
    added support for using EDMA on peripherals which have no direct EDMA
    event mapping.
    
    The code compiles and does not explode in your face, but that's it.
    
    1) Reading an u16 array from an u32 device tree array simply does not
       work. Even if the function is named "edma_of_read_u32_to_s16_array".
    
       It merily calls of_property_read_u16_array. So the resulting 16bit
       array will have every other entry = 0.
    
    2) The DT entry for the xbar registers related to xbar has length 0x10
       instead of the real length: 0xfd0 - 0xf90 = 0x40.
    
       Not a real problem as it does not cross a page boundary, but
       wrong nevertheless.
    
    3) But none of this matters as the mapping never happens:
    
       After reading nonsense edma_of_read_u32_to_s16_array() invalidates
       the first array entry pair, so nobody can ever notice the
       braindamage by immediate explosion.
    
    Seems the QA criteria for this code was solely not to explode when
    someone adds edma-xbar-event-map entries to the DT. Goal achieved,
    congratulations!
    
    Not really helpful if someone wants to use edma on a device which
    requires a xbar mapping.
    
    Fix the issues by:
    
    - annotating the device tree entry with "/bits/ 16" as documented in
      the of_property_read_u16_array kernel doc
    
    - make the size of the xbar register mapping correct
    
    - invalidating the end of the array and not the start
    
    This convoluted mess wants to be completely rewritten as there is no
    point to keep the xbar_chan array memory and the iomapping of the xbar
    regs around forever. Marking the xbar mapped channels as used should
    be done right there.
    
    But that's a different issue and this patch is small enough to make it
    work and allows a simple backport for stable.
    
    Cc: stable@vger.kernel.org # v3.12+
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarSekhar Nori <nsekhar@ti.com>
    cf7eb979
edma.c 48.7 KB