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Commit 7349a69cf312 ("iopoll: Do not use > timekeeping in read_poll_timeout_atomic()") changed the behavior to no > longer use ktime_get at the expense of underestimation of wall clock > time which appears to be very large for delay_us=0. Instead of timing > out after approximately XILINX_DMA_LOOP_COUNT microseconds, the timeout > takes XILINX_DMA_LOOP_COUNT * 1000 * (time that the overhead of the for > loop in poll_timeout_us_atomic takes) which is in the range of several > minutes for XILINX_DMA_LOOP_COUNT=1000000. Fix this by using a non-zero > value for delay_us. Use delay_us=10 to keep the delay in the hot path of > starting DMA transfers minimal but still avoid CPU stalls in case of > unexpected hardware failures. > > One-off measurement with delay_us=0 causes the cpu to busy wait around 7 > minutes in the timeout case. After applying this patch with delay_us=10 > the measured timeout was 1053428 microseconds which is roughly > equivalent to the expected 1000000 microseconds specified in > XILINX_DMA_LOOP_COUNT. > > Add a constant XILINX_DMA_POLL_DELAY_US for delay_us value. > > Fixes: 9495f2648287 ("dmaengine: xilinx_vdma: Use readl_poll_timeout instead of do while loop's") > Fixes: 7349a69cf312 ("iopoll: Do not use timekeeping in read_poll_timeout_atomic()") > Signed-off-by: Alex Bereza > --- Reviewed-by: Frank Li > drivers/dma/xilinx/xilinx_dma.c | 14 ++++++++++---- > 1 file changed, 10 insertions(+), 4 deletions(-) > > diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c > index 02a05f215614..345a738bab2c 100644 > --- a/drivers/dma/xilinx/xilinx_dma.c > +++ b/drivers/dma/xilinx/xilinx_dma.c > @@ -167,6 +167,8 @@ > > /* Delay loop counter to prevent hardware failure */ > #define XILINX_DMA_LOOP_COUNT 1000000 > +/* Delay between polls (avoid a delay of 0 to prevent CPU stalls) */ > +#define XILINX_DMA_POLL_DELAY_US 10 > > /* AXI DMA Specific Registers/Offsets */ > #define XILINX_DMA_REG_SRCDSTADDR 0x18 > @@ -1332,7 +1334,8 @@ static int xilinx_dma_stop_transfer(struct xilinx_dma_chan *chan) > > /* Wait for the hardware to halt */ > return xilinx_dma_poll_timeout(chan, XILINX_DMA_REG_DMASR, val, > - val & XILINX_DMA_DMASR_HALTED, 0, > + val & XILINX_DMA_DMASR_HALTED, > + XILINX_DMA_POLL_DELAY_US, > XILINX_DMA_LOOP_COUNT); > } > > @@ -1347,7 +1350,8 @@ static int xilinx_cdma_stop_transfer(struct xilinx_dma_chan *chan) > u32 val; > > return xilinx_dma_poll_timeout(chan, XILINX_DMA_REG_DMASR, val, > - val & XILINX_DMA_DMASR_IDLE, 0, > + val & XILINX_DMA_DMASR_IDLE, > + XILINX_DMA_POLL_DELAY_US, > XILINX_DMA_LOOP_COUNT); > } > > @@ -1364,7 +1368,8 @@ static void xilinx_dma_start(struct xilinx_dma_chan *chan) > > /* Wait for the hardware to start */ > err = xilinx_dma_poll_timeout(chan, XILINX_DMA_REG_DMASR, val, > - !(val & XILINX_DMA_DMASR_HALTED), 0, > + !(val & XILINX_DMA_DMASR_HALTED), > + XILINX_DMA_POLL_DELAY_US, > XILINX_DMA_LOOP_COUNT); > > if (err) { > @@ -1780,7 +1785,8 @@ static int xilinx_dma_reset(struct xilinx_dma_chan *chan) > > /* Wait for the hardware to finish reset */ > err = xilinx_dma_poll_timeout(chan, XILINX_DMA_REG_DMACR, tmp, > - !(tmp & XILINX_DMA_DMACR_RESET), 0, > + !(tmp & XILINX_DMA_DMACR_RESET), > + XILINX_DMA_POLL_DELAY_US, > XILINX_DMA_LOOP_COUNT); > > if (err) { > > -- > 2.53.0 >