linux-kernel - Re: [PATCH v7 1/8] dmaengine: add DMA_PREP_LOCK and DMA_PREP

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Message-ID: <ozcg3m3iwdprt4hnti473e4j6ixnwgggbdvsnxold32bigcv7i@koo3ww3wfw22>
Date: Tue, 11 Mar 2025 17:59:55 +0200
From: Dmitry Baryshkov <lumag@...nel.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Thara Gopinath <thara.gopinath@...il.com>, 
	Herbert Xu <herbert@...dor.apana.org.au>, "David S. Miller" <davem@...emloft.net>, 
	Vinod Koul <vkoul@...nel.org>, Jonathan Corbet <corbet@....net>, 
	Md Sadre Alam <quic_mdalam@...cinc.com>, Srinivas Kandagatla <srinivas.kandagatla@...aro.org>, 
	linux-crypto@...r.kernel.org, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	dmaengine@...r.kernel.org, linux-doc@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v7 1/8] dmaengine: add DMA_PREP_LOCK and DMA_PREP_UNLOCK
 flag

On Tue, Mar 11, 2025 at 10:25:32AM +0100, Bartosz Golaszewski wrote:
> From: Md Sadre Alam <quic_mdalam@...cinc.com>
> 
> Add lock and unlock flags for the command descriptor. With the former set
> in the requester pipe, the bam controller will lock all other pipes and
> process the request only from requester pipe. Unlocking can only be
> performed from the same pipe.
> 
> Setting the DMA_PREP_LOCK/DMA_PREP_UNLOCK flags in the command
> descriptor means, the caller requests the BAM controller to be locked
> for the duration of the transaction. In this case the BAM driver must
> set the LOCK/UNLOCK bits in the HW descriptor respectively.
> 
> Only BAM IPs version 1.4.0 and above support the LOCK/UNLOCK feature.

You are describing behaviour (and even versions) of a particular DMA
hardware (BAM) in the commit message for a generic flag. Please drop all
of that. Generic code should be described in generic terms.

> 
> Signed-off-by: Md Sadre Alam <quic_mdalam@...cinc.com>
> [Bartosz: reworked the commit message]
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> ---
>  Documentation/driver-api/dmaengine/provider.rst | 15 +++++++++++++++
>  include/linux/dmaengine.h                       |  6 ++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst
> index 3085f8b460fa..a032e55d0a4f 100644
> --- a/Documentation/driver-api/dmaengine/provider.rst
> +++ b/Documentation/driver-api/dmaengine/provider.rst
> @@ -628,6 +628,21 @@ DMA_CTRL_REUSE
>    - This flag is only supported if the channel reports the DMA_LOAD_EOT
>      capability.
>  
> +- DMA_PREP_LOCK
> +
> +  - If set, the DMA will lock all other pipes not related to the current
> +    pipe group, and keep handling the current pipe only.
> +
> +  - All pipes not within this group will be locked by this pipe upon lock
> +    event.
> +
> +  - only pipes which are in the same group and relate to the same Environment
> +    Execution(EE) will not be locked by a certain pipe.
> +
> +- DMA_PREP_UNLOCK
> +
> +  - If set, DMA will release all locked pipes
> +
>  General Design Notes
>  ====================
>  
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 346251bf1026..8ebd43a998a7 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),
>  };
>  
>  /**
> 
> -- 
> 2.45.2
> 

-- 
With best wishes
Dmitry