Re: [PATCH v8 01/11] dmaengine: Add DMA_PREP_LOCK/DMA_PREP_UNLOCK flags

[Dmitry Baryshkov]

On Thu, Nov 06, 2025 at 12:33:57PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> 
> Some DMA engines may be accessed from linux and the TrustZone
> simultaneously. In order to allow synchronization, add lock and unlock
> flags for the command descriptor that allow the caller to request the
> controller to be locked for the duration of the transaction in an
> implementation-dependent way.

What is the expected behaviour if Linux "locks" the engine and then TZ
tries to use it before Linux has a chance to unlock it.

> 
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> ---
>  Documentation/driver-api/dmaengine/provider.rst | 9 +++++++++
>  include/linux/dmaengine.h                       | 6 ++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst
> index 1594598b331782e4dddcf992159c724111db9cf3..6428211405472dd1147e363f5786acc91d95ed43 100644
> --- a/Documentation/driver-api/dmaengine/provider.rst
> +++ b/Documentation/driver-api/dmaengine/provider.rst
> @@ -630,6 +630,15 @@ DMA_CTRL_REUSE
>    - This flag is only supported if the channel reports the DMA_LOAD_EOT
>      capability.
>  
> +- DMA_PREP_LOCK
> +
> +  - If set, the DMA controller will be locked for the duration of the current
> +    transaction.
> +
> +- DMA_PREP_UNLOCK
> +
> +  - If set, DMA will release he controller lock.
> +
>  General Design Notes
>  ====================
>  
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 99efe2b9b4ea9844ca6161208362ef18ef111d96..c02be4bc8ac4c3db47c7c11751b949e3479e7cb8 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -200,6 +200,10 @@ struct dma_vec {
>   *  transaction is marked with DMA_PREP_REPEAT will cause the new transaction
>   *  to never be processed and stay in the issued queue forever. The flag is
>   *  ignored if the previous transaction is not a repeated transaction.
> + *  @DMA_PREP_LOCK: tell the driver that there is a lock bit set on command
> + *  descriptor.
> + *  @DMA_PREP_UNLOCK: tell the driver that there is a un-lock bit set on command
> + *  descriptor.
>   */
>  enum dma_ctrl_flags {
>  	DMA_PREP_INTERRUPT = (1 << 0),
> @@ -212,6 +216,8 @@ enum dma_ctrl_flags {
>  	DMA_PREP_CMD = (1 << 7),
>  	DMA_PREP_REPEAT = (1 << 8),
>  	DMA_PREP_LOAD_EOT = (1 << 9),
> +	DMA_PREP_LOCK = (1 << 10),
> +	DMA_PREP_UNLOCK = (1 << 11),
>  };
>  
>  /**
> 
> -- 
> 2.51.0
> 

-- 
With best wishes
Dmitry