mmc: mxcmmc: fix race condition when dma finish a data transfer
mmc: mxcmmc: fix race condition when dma finish a data transfer

During a read of data block using dma, driver might have two ways to finish to read
and free the resources:
1) checking STATUS_DATA_TRANS_DONE mask, in the mxcmci_irq() routine
   (pending to mmc irq)
2) mxmmc driver, registers also a mxcmci_dma_callback() and when transfer is finished,
   dma driver calls this callback. (pending to dma irq)
Both ways are concurrent with each other.

Race condition happens when following events occur:
/* (1) mxcmci driver start data transfer */
         158.418970: mpc_dma_execute: mpc_dma_execute(): will_access_peripheral start cid=31
         158.418976: mpc_dma_issue_pending <-mxcmci_request
         158.418983: mxcmci_start_cmd <-mxcmci_request
/* (2) mxcmci driver receive mmc irq */
         158.419656: mxcmci_irq <-handle_irq_event_percpu
         158.419692: mxcmci_read_response <-mxcmci_irq
/* (3) mxcmci driver checks that transfer is complete and call mxcmci_finish_data() */
         158.419726: mxcmci_data_done <-mxcmci_irq
         158.419729: mxcmci_finish_data <-mxcmci_data_done
         158.419733: dma_direct_unmap_sg <-mxcmci_finish_data
         158.419736: mxcmci_swap_buffers.isra.24 <-mxcmci_finish_data
         158.419762: mxcmci_read_response <-mxcmci_data_done
/* (4) mxcmci driver (no dma): send stop command */
         158.419765: mxcmci_start_cmd <-mxcmci_data_done
/* (5) mxcmci driver (no dma): receive the stop command irq response */
         158.419782: mxcmci_irq <-handle_irq_event_percpu
         158.419812: mxcmci_read_response <-mxcmci_irq
         158.419843: mxcmci_finish_request <-mxcmci_irq
/* (6) dma driver: receive dma irq (finish data transfer) related by request on step 1 */
         158.419853: mpc_dma_irq <-handle_irq_event_percpu
         158.420001: mpc_dma_irq_process <-mpc_dma_irq
         158.420004: mpc_dma_irq_process <-mpc_dma_irq
/* (7) dma driver: start dma tasklet to finish the dma irq handling */
         158.420008: mpc_dma_irq_process: mpc_dma_irq_process(): completed ch:31
/* (8) mxcmci driver: start next data transfer using dma */
         158.420174: mxcmci_request <-mmc_start_req
         158.420182: dma_direct_map_sg <-mxcmci_request
         158.420192: mpc_dma_prep_slave_sg <-mxcmci_request
/* (9) dma driver: schedule irq tasklet and execute mxcmci dma driver callback */
         158.420250: mpc_dma_tasklet <-tasklet_action
         158.420254: mpc_dma_process_completed <-tasklet_action
         158.420267: mxcmci_dma_callback <-mpc_dma_process_completed
/* ERROR!!! (10) mxcmci driver callback works on dma data related to the step 1
                 that is already finished */
         158.420271: mxcmci_data_done <-mpc_dma_process_completed
         158.420273: mxcmci_finish_data <-mxcmci_data_done
/* ERROR!!! (11) mxcmci driver: clear data that should be used by step 8 and
                 send an other mmc stop command (already sended on step 4) */
         158.420276: dma_direct_unmap_sg <-mxcmci_finish_data
         158.420279: mxcmci_swap_buffers.isra.24 <-mxcmci_finish_data
         158.420330: mxcmci_read_response <-mxcmci_data_done
         158.420333: mxcmci_start_cmd <-mxcmci_data_done
         158.420338: dma_run_dependencies <-mpc_dma_process_completed
...
...
...
         168.474223: mxcmci_watchdog <-call_timer_fn
         168.474236: mxcmci_watchdog: mxcmci_watchdog
         168.474397: mpc_dma_device_control <-mxcmci_watchdog

In accordance with the other drivers that using the dma engine,
fix it, leaving *only* to dma driver the complete control to
ending the read operation.

Removing STATUS_READ_OP_DONE event activation, has as effect
to force mxcmci driver to handle the finish data transfer only
by mxcmci dma callback.

Signed-off-by: Matteo Facchinetti <5b25c955c24ffbca193a914258e9119dd2ee75f5@sirius-es.it>
Acked-by: Sascha Hauer <c00cbc2b736c26791a3822db86f8796fe9efff67@pengutronix.de>
Signed-off-by: Ulf Hansson <fe47b31f388f85ce6ddf64bf3a0cf6b46077d0e6@linaro.org>

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