• Sekhar Nori's avatar
    dma: edma: fix incorrect SG list handling · 5fc68a6c
    Sekhar Nori authored
    The code to handle any length SG lists calls edma_resume()
    even before edma_start() is called. This is incorrect
    because edma_resume() enables edma events on the channel
    after which CPU (in edma_start) cannot clear posted
    events by writing to ECR (per the EDMA user's guide).
    
    Because of this EDMA transfers fail to start if due
    to some reason there is a pending EDMA event registered
    even before EDMA transfers are started. This can happen if
    an EDMA event is a byproduct of device initialization.
    
    Fix this by calling edma_resume() only if it is not the
    first batch of MAX_NR_SG elements.
    
    Without this patch, MMC/SD fails to function on DA850 EVM
    with DMA. The behaviour is triggered by specific IP and
    this can explain why the issue was not reported before
    (example with MMC/SD on AM335x).
    
    Tested on DA850 EVM and AM335x EVM-SK using MMC/SD card.
    
    Cc: stable@vger.kernel.org # v3.12.x+
    Cc: Joel Fernandes <joelf@ti.com>
    Acked-by: default avatarJoel Fernandes <joelf@ti.com>
    Tested-by: default avatarJon Ringle <jringle@gridpoint.com>
    Tested-by: default avatarAlexander Holler <holler@ahsoftware.de>
    Reported-by: default avatarJon Ringle <jringle@gridpoint.com>
    Signed-off-by: default avatarSekhar Nori <nsekhar@ti.com>
    Signed-off-by: default avatarVinod Koul <vinod.koul@intel.com>
    5fc68a6c
edma.c 24.5 KB