linux-kernel - Re: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit support

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Message-ID: <6c85436d-e064-367e-736b-951af82256c8@linaro.org>
Date:   Fri, 18 Dec 2020 22:35:17 -0500
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Md Sadre Alam <mdalam@...eaurora.org>, vkoul@...nel.org,
        corbet@....net, agross@...nel.org, bjorn.andersson@...aro.org,
        dan.j.williams@...el.com, dmaengine@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Cc:     sricharan@...eaurora.org
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit
 support



On 12/17/20 9:37 AM, Md Sadre Alam wrote:
> This change will add support for LOCK & UNLOCK flag bit support
> on CMD descriptor.
> 
> If DMA_PREP_LOCK flag passed in prep_slave_sg then requester of this
> transaction wanted to lock the DMA controller for this transaction so
> BAM driver should set LOCK bit for the HW descriptor.
> 
> If DMA_PREP_UNLOCK flag passed in prep_slave_sg then requester of this
> transaction wanted to unlock the DMA controller.so BAM driver should set
> UNLOCK bit for the HW descriptor.
Hi,

This is a generic question. What is the point of LOCK/UNLOCK with 
allocating LOCK groups to the individual dma channels? By default
doesn't all channels fall in the same group. This would mean that
a lock does not prevent the dma controller from not executing a
transaction on the other channels.

-- 
Warm Regards
Thara

> 
> Signed-off-by: Md Sadre Alam <mdalam@...eaurora.org>
> ---
>   Documentation/driver-api/dmaengine/provider.rst | 9 +++++++++
>   drivers/dma/qcom/bam_dma.c                      | 9 +++++++++
>   include/linux/dmaengine.h                       | 5 +++++
>   3 files changed, 23 insertions(+)
> 
> diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst
> index ddb0a81..d7516e2 100644
> --- a/Documentation/driver-api/dmaengine/provider.rst
> +++ b/Documentation/driver-api/dmaengine/provider.rst
> @@ -599,6 +599,15 @@ DMA_CTRL_REUSE
>     - This flag is only supported if the channel reports the DMA_LOAD_EOT
>       capability.
>   
> +- DMA_PREP_LOCK
> +
> +  - If set , the client driver tells DMA controller I am locking you for
> +    this transcation.
> +
> +- DMA_PREP_UNLOCK
> +
> +  - If set, the client driver will tells DMA controller I am releasing the lock
> +
>   General Design Notes
>   ====================
>   
> diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> index 4eeb8bb..cdbe395 100644
> --- a/drivers/dma/qcom/bam_dma.c
> +++ b/drivers/dma/qcom/bam_dma.c
> @@ -58,6 +58,8 @@ struct bam_desc_hw {
>   #define DESC_FLAG_EOB BIT(13)
>   #define DESC_FLAG_NWD BIT(12)
>   #define DESC_FLAG_CMD BIT(11)
> +#define DESC_FLAG_LOCK BIT(10)
> +#define DESC_FLAG_UNLOCK BIT(9)
>   
>   struct bam_async_desc {
>   	struct virt_dma_desc vd;
> @@ -644,6 +646,13 @@ static struct dma_async_tx_descriptor *bam_prep_slave_sg(struct dma_chan *chan,
>   
>   	/* fill in temporary descriptors */
>   	desc = async_desc->desc;
> +	if (flags & DMA_PREP_CMD) {
> +		if (flags & DMA_PREP_LOCK)
> +			desc->flags |= cpu_to_le16(DESC_FLAG_LOCK);
> +		if (flags & DMA_PREP_UNLOCK)
> +			desc->flags |= cpu_to_le16(DESC_FLAG_UNLOCK);
> +	}
> +
>   	for_each_sg(sgl, sg, sg_len, i) {
>   		unsigned int remainder = sg_dma_len(sg);
>   		unsigned int curr_offset = 0;
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index dd357a7..79ccadb4 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -190,6 +190,9 @@ struct dma_interleaved_template {
>    *  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 DMA HW engine going to be locked for this
> + *  transaction , until not seen DMA_PREP_UNLOCK flag set.
> + * @DMA_PREP_UNLOCK: tell the driver to unlock the DMA HW engine.
>    */
>   enum dma_ctrl_flags {
>   	DMA_PREP_INTERRUPT = (1 << 0),
> @@ -202,6 +205,8 @@ 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),
>   };
>   
>   /**
>