diff options
| author | Alex Bereza <alex@bereza.email> | 2026-04-02 09:46:22 +0200 |
|---|---|---|
| committer | Vinod Koul <vkoul@kernel.org> | 2026-07-02 21:13:10 +0530 |
| commit | aa99c4d1d63bbc26a5fc4c667d89b2595743c19d (patch) | |
| tree | b857e3ceee4b7d66893c53f9efc2a8043e875518 /drivers | |
| parent | cbabdd6ce1b313b5877c7fbb2f5e2f7936564d2f (diff) | |
dmaengine: xilinx_dma: Fix CPU stall in xilinx_dma_poll_timeout
Currently when calling xilinx_dma_poll_timeout with delay_us=0 and a
condition that is never fulfilled, the CPU busy-waits for prolonged time
and the timeout triggers only with a massive delay causing a CPU stall.
This happens due to a huge underestimation of wall clock time in
poll_timeout_us_atomic. 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()")
Reviewed-by: Suraj Gupta <suraj.gupta2@amd.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Alex Bereza <alex@bereza.email>
Link: https://patch.msgid.link/20260402-fix-atomic-poll-timeout-regression-v4-1-f30d6a6c13cb@bereza.email
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/dma/xilinx/xilinx_dma.c | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c index 829601d8a16f..ddf9635809d3 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 @@ -1324,7 +1326,8 @@ 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); } @@ -1339,7 +1342,8 @@ 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); } @@ -1356,7 +1360,8 @@ 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) { @@ -1800,7 +1805,8 @@ 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) { |