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dmaengine: dw: Add memory bus width verification
[ Upstream commit d04b21b ] Currently in case of the DEV_TO_MEM or MEM_TO_DEV DMA transfers the memory data width (single transfer width) is determined based on the buffer length, buffer base address or DMA master-channel max address width capability. It isn't enough in case of the channel disabling prior the block transfer is finished. Here is what DW AHB DMA IP-core databook says regarding the port suspension (DMA-transfer pause) implementation in the controller: "When CTLx.SRC_TR_WIDTH < CTLx.DST_TR_WIDTH and the CFGx.CH_SUSP bit is high, the CFGx.FIFO_EMPTY is asserted once the contents of the FIFO do not permit a single word of CTLx.DST_TR_WIDTH to be formed. However, there may still be data in the channel FIFO, but not enough to form a single transfer of CTLx.DST_TR_WIDTH. In this scenario, once the channel is disabled, the remaining data in the channel FIFO is not transferred to the destination peripheral." So in case if the port gets to be suspended and then disabled it's possible to have the data silently discarded even though the controller reported that FIFO is empty and the CTLx.BLOCK_TS indicated the dropped data already received from the source device. This looks as if the data somehow got lost on a way from the peripheral device to memory and causes problems for instance in the DW APB UART driver, which pauses and disables the DMA-transfer as soon as the recv data timeout happens. Here is the way it looks: Memory <------- DMA FIFO <------ UART FIFO <---------------- UART DST_TR_WIDTH -+--------| | | | | | | No more data Current lvl -+--------| |---------+- DMA-burst lvl | | |---------+- Leftover data | | |---------+- SRC_TR_WIDTH -+--------+-------+---------+ In the example above: no more data is getting received over the UART port and BLOCK_TS is not even close to be fully received; some data is left in the UART FIFO, but not enough to perform a bursted DMA-xfer to the DMA FIFO; some data is left in the DMA FIFO, but not enough to be passed further to the system memory in a single transfer. In this situation the 8250 UART driver catches the recv timeout interrupt, pauses the DMA-transfer and terminates it completely, after which the IRQ handler manually fetches the leftover data from the UART FIFO into the recv-buffer. But since the DMA-channel has been disabled with the data left in the DMA FIFO, that data will be just discarded and the recv-buffer will have a gap of the "current lvl" size in the recv-buffer at the tail of the lately received data portion. So the data will be lost just due to the misconfigured DMA transfer. Note this is only relevant for the case of the transfer suspension and _disabling_. No problem will happen if the transfer will be re-enabled afterwards or the block transfer is fully completed. In the later case the "FIFO flush mode" will be executed at the transfer final stage in order to push out the data left in the DMA FIFO. In order to fix the denoted problem the DW AHB DMA-engine driver needs to make sure that the _bursted_ source transfer width is greater or equal to the single destination transfer (note the HW databook describes more strict constraint than actually required). Since the peripheral-device side is prescribed by the client driver logic, the memory-side can be only used for that. The solution can be easily implemented for the DEV_TO_MEM transfers just by adjusting the memory-channel address width. Sadly it's not that easy for the MEM_TO_DEV transfers since the mem-to-dma burst size is normally dynamically determined by the controller. So the only thing that can be done is to make sure that memory-side address width is greater than the peripheral device address width. Fixes: a098200 ("dw_dmac: autoconfigure data_width or get it via platform data") Signed-off-by: Serge Semin <[email protected]> Acked-by: Andy Shevchenko <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Vinod Koul <[email protected]> Signed-off-by: Sasha Levin <[email protected]>
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