linux-kernel - [PATCH v2] dmaengine: pl330: Fix unbalanced runtime PM

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Date:   Wed, 20 Apr 2022 18:27:36 +0800
From:   Sugar Zhang <sugar.zhang@...k-chips.com>
To:     vkoul@...nel.org
Cc:     Sugar Zhang <sugar.zhang@...k-chips.com>,
        Huibin Hong <huibin.hong@...k-chips.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Russell King <rmk+kernel@....linux.org.uk>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] dmaengine: pl330: Fix unbalanced runtime PM

This driver use runtime PM autosuspend mechanism to manager clk.

  pm_runtime_use_autosuspend(&adev->dev);
  pm_runtime_set_autosuspend_delay(&adev->dev, PL330_AUTOSUSPEND_DELAY);

So, after ref count reached to zero, it will enter suspend
after the delay time elapsed.

The unbalanced PM:

* May cause dmac the next start failed.
* May cause dmac read unexpected state.
* May cause dmac stall if power down happen at the middle of the transfer.
  e.g. may lose ack from AXI bus and stall.

Considering the following situation:

      DMA TERMINATE               TASKLET ROUTINE
            |                            |
            |                       issue_pending
            |                            |
            |                     pch->active = true
            |                       pm_runtime_get
  pm_runtime_put(if active)              |
    pch->active = false                  |
            |                      work_list empty
            |                            |
            |                     pm_runtime_put(unconditional)
            |                            |

At this point, it's unbalanced(1 get / 2 put).

After this patch:

      DMA TERMINATE               TASKLET ROUTINE
            |                            |
            |                       issue_pending
            |                            |
            |                     pch->active = true
            |                       pm_runtime_get
  pm_runtime_put(if active)              |
    pch->active = false                  |
            |                      work_list empty
            |                            |
            |                   pm_runtime_put(if active)
            |                            |

Now, it's balanced(1 get / 1 put).

Fixes: 5c9e6c2b2ba3 ("dmaengine: pl330: Fix runtime PM support for terminated transfers")
Fixes: ae43b3289186 ("ARM: 8202/1: dmaengine: pl330: Add runtime Power Management support v12")

Signed-off-by: Huibin Hong <huibin.hong@...k-chips.com>
Signed-off-by: Sugar Zhang <sugar.zhang@...k-chips.com>

---

Changes in v2:
- fixup commit message per Vinod suggestion.

 drivers/dma/pl330.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
index 858400e..ccd430e 100644
--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c
@@ -2084,7 +2084,7 @@ static void pl330_tasklet(struct tasklet_struct *t)
 		spin_lock(&pch->thread->dmac->lock);
 		_stop(pch->thread);
 		spin_unlock(&pch->thread->dmac->lock);
-		power_down = true;
+		power_down = pch->active;
 		pch->active = false;
 	} else {
 		/* Make sure the PL330 Channel thread is active */
-- 
2.7.4