[PATCH 0/3] dmaengine: Use non-atomic bit ops where safe

[PATCH 0/3] dmaengine: Use non-atomic bit ops where safe

[Peng Fan (OSS)]

dma_cap_set()/dma_cap_clear() and imx-sdma event_mask setup use atomic
set_bit()/clear_bit() in contexts where no concurrent access is
possible:

- dma_cap_set()/dma_cap_clear() are called exclusively during driver
  probe, before dma_async_device_register() makes the device visible.
- imx-sdma event_mask[] is zeroed and configured during channel setup
  while the channel is disabled.

Switch both to non-atomic __set_bit()/__clear_bit() equivalents.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
Peng Fan (3):
      dmaengine: Use non-atomic bit ops for cap_mask manipulation
      dmaengine: imx-sdma: Use non-atomic __set_bit() for event_mask setup
      dmaengine: imx-sdma: Use __assign_bit() for ownership configuration

 drivers/dma/imx-sdma.c    | 21 +++++----------------
 include/linux/dmaengine.h |  4 ++--
 2 files changed, 7 insertions(+), 18 deletions(-)
---
base-commit: 89c07d98716a13454ec3fd9f97689e812cc71bd4
change-id: 20260903-dma-mask-ddf64d770f7d

Best regards,
--  
Peng Fan <peng.fan@nxp.com>

[PATCH 1/3] dmaengine: Use non-atomic bit ops for cap_mask manipulation

[Peng Fan (OSS)]

From: Peng Fan <peng.fan@nxp.com>

dma_cap_set() and dma_cap_clear() are called exclusively during driver
probe, before dma_async_device_register() makes the device visible to
the rest of the system. There is no concurrent access to cap_mask at
that point, so switch to the non-atomic __set_bit()/__clear_bit()
equivalents.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 include/linux/dmaengine.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index fe33a20abc614..923d914691d06 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -1551,14 +1551,14 @@ static inline bool async_tx_test_ack(struct dma_async_tx_descriptor *tx)
 static inline void
 __dma_cap_set(enum dma_transaction_type tx_type, dma_cap_mask_t *dstp)
 {
-	set_bit(tx_type, dstp->bits);
+	__set_bit(tx_type, dstp->bits);
 }
 
 #define dma_cap_clear(tx, mask) __dma_cap_clear((tx), &(mask))
 static inline void
 __dma_cap_clear(enum dma_transaction_type tx_type, dma_cap_mask_t *dstp)
 {
-	clear_bit(tx_type, dstp->bits);
+	__clear_bit(tx_type, dstp->bits);
 }
 
 #define dma_cap_zero(mask) __dma_cap_zero(&(mask))

-- 
2.34.1

[PATCH 2/3] dmaengine: imx-sdma: Use non-atomic __set_bit() for event_mask setup

[Peng Fan (OSS)]

From: Peng Fan <peng.fan@nxp.com>

In sdma_set_watermarklevel_for_p2p(), the event_mask[] fields are zeroed
in sdma_config_channel() right before this function is called, and the
channel has already been disabled. There is no concurrent access to
event_mask at this point, so replace set_bit() with __set_bit().

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 drivers/dma/imx-sdma.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
index 36368835a845c..63261ab6402b9 100644
--- a/drivers/dma/imx-sdma.c
+++ b/drivers/dma/imx-sdma.c
@@ -1241,8 +1241,8 @@ static void sdma_set_watermarklevel_for_p2p(struct sdma_channel *sdmac)
 	int lwml = sdmac->watermark_level & SDMA_WATERMARK_LEVEL_LWML;
 	int hwml = (sdmac->watermark_level & SDMA_WATERMARK_LEVEL_HWML) >> 16;
 
-	set_bit(sdmac->event_id0 % 32, &sdmac->event_mask[1]);
-	set_bit(sdmac->event_id1 % 32, &sdmac->event_mask[0]);
+	__set_bit(sdmac->event_id0 % 32, &sdmac->event_mask[1]);
+	__set_bit(sdmac->event_id1 % 32, &sdmac->event_mask[0]);
 
 	if (sdmac->event_id0 > 31)
 		sdmac->watermark_level |= SDMA_WATERMARK_LEVEL_LWE;

-- 
2.34.1

[PATCH 3/3] dmaengine: imx-sdma: Use __assign_bit() for ownership configuration

[Peng Fan (OSS)]

From: Peng Fan <peng.fan@nxp.com>

Replace the if/else pairs of __set_bit()/__clear_bit() in
sdma_config_ownership() with __assign_bit(), which does exactly the
same conditional set-or-clear in a single call.

No functional change.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 drivers/dma/imx-sdma.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
index 63261ab6402b9..da565409beaaa 100644
--- a/drivers/dma/imx-sdma.c
+++ b/drivers/dma/imx-sdma.c
@@ -710,20 +710,9 @@ static int sdma_config_ownership(struct sdma_channel *sdmac,
 	mcu = readl_relaxed(sdma->regs + SDMA_H_HOSTOVR);
 	dsp = readl_relaxed(sdma->regs + SDMA_H_DSPOVR);
 
-	if (dsp_override)
-		__clear_bit(channel, &dsp);
-	else
-		__set_bit(channel, &dsp);
-
-	if (event_override)
-		__clear_bit(channel, &evt);
-	else
-		__set_bit(channel, &evt);
-
-	if (mcu_override)
-		__clear_bit(channel, &mcu);
-	else
-		__set_bit(channel, &mcu);
+	__assign_bit(channel, &dsp, !dsp_override);
+	__assign_bit(channel, &evt, !event_override);
+	__assign_bit(channel, &mcu, !mcu_override);
 
 	writel_relaxed(evt, sdma->regs + SDMA_H_EVTOVR);
 	writel_relaxed(mcu, sdma->regs + SDMA_H_HOSTOVR);

-- 
2.34.1

Re: [PATCH 0/3] dmaengine: Use non-atomic bit ops where safe

[Frank Li]

On Thu, Sep 03, 2026 at 10:16:11PM +0800, Peng Fan (OSS) wrote:
> dma_cap_set()/dma_cap_clear() and imx-sdma event_mask setup use atomic
> set_bit()/clear_bit() in contexts where no concurrent access is
> possible:
>
> - dma_cap_set()/dma_cap_clear() are called exclusively during driver
>   probe, before dma_async_device_register() makes the device visible.
> - imx-sdma event_mask[] is zeroed and configured during channel setup
>   while the channel is disabled.
>
> Switch both to non-atomic __set_bit()/__clear_bit() equivalents.

Any benefit to switch?

Frank

>
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
> Peng Fan (3):
>       dmaengine: Use non-atomic bit ops for cap_mask manipulation
>       dmaengine: imx-sdma: Use non-atomic __set_bit() for event_mask setup
>       dmaengine: imx-sdma: Use __assign_bit() for ownership configuration
>
>  drivers/dma/imx-sdma.c    | 21 +++++----------------
>  include/linux/dmaengine.h |  4 ++--
>  2 files changed, 7 insertions(+), 18 deletions(-)
> ---
> base-commit: 89c07d98716a13454ec3fd9f97689e812cc71bd4
> change-id: 20260903-dma-mask-ddf64d770f7d
>
> Best regards,
> --
> Peng Fan <peng.fan@nxp.com>
>