linux-kernel - Re: [PATCH v9 03/11] dmaengine: qcom: bam_dma: implement support for BAM locking

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Message-ID: <aUFX14nz8cQj8EIb@vaman>
Date: Tue, 16 Dec 2025 18:30:07 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Jonathan Corbet <corbet@....net>,
	Thara Gopinath <thara.gopinath@...il.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Udit Tiwari <quic_utiwari@...cinc.com>,
	Daniel Perez-Zoghbi <dperezzo@...cinc.com>,
	Md Sadre Alam <mdalam@....qualcomm.com>,
	Dmitry Baryshkov <lumag@...nel.org>, dmaengine@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-crypto@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v9 03/11] dmaengine: qcom: bam_dma: implement support for
 BAM locking

On 28-11-25, 12:44, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> Use metadata operations in DMA descriptors to allow BAM users to pass
> additional information to the engine. To that end: define a new
> structure - struct bam_desc_metadata - as a medium and define two new
> commands: for locking and unlocking the BAM respectively. Handle the
> locking in the .attach() callback.
> 
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> ---
>  drivers/dma/qcom/bam_dma.c       | 59 +++++++++++++++++++++++++++++++++++++++-
>  include/linux/dma/qcom_bam_dma.h | 12 ++++++++
>  2 files changed, 70 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> index c9ae1fffe44d79c5eb59b8bbf7f147a8fa3aa0bd..d1dc80b29818897b333cd223ec7306a169cc51fd 100644
> --- a/drivers/dma/qcom/bam_dma.c
> +++ b/drivers/dma/qcom/bam_dma.c
> @@ -30,6 +30,7 @@
>  #include <linux/module.h>
>  #include <linux/interrupt.h>
>  #include <linux/dma-mapping.h>
> +#include <linux/dma/qcom_bam_dma.h>
>  #include <linux/scatterlist.h>
>  #include <linux/device.h>
>  #include <linux/platform_device.h>
> @@ -391,6 +392,8 @@ struct bam_chan {
>  	struct list_head desc_list;
>  
>  	struct list_head node;
> +
> +	bool bam_locked;
>  };
>  
>  static inline struct bam_chan *to_bam_chan(struct dma_chan *common)
> @@ -655,6 +658,53 @@ static int bam_slave_config(struct dma_chan *chan,
>  	return 0;
>  }
>  
> +static int bam_metadata_attach(struct dma_async_tx_descriptor *desc, void *data, size_t len)
> +{
> +	struct virt_dma_desc *vd = container_of(desc, struct virt_dma_desc, tx);
> +	struct bam_async_desc *async_desc = container_of(vd, struct bam_async_desc,  vd);
> +	struct bam_desc_hw *hw_desc = async_desc->desc;
> +	struct bam_desc_metadata *metadata = data;
> +	struct bam_chan *bchan = to_bam_chan(metadata->chan);
> +	struct bam_device *bdev = bchan->bdev;
> +
> +	if (!data)
> +		return -EINVAL;
> +
> +	if (metadata->op == BAM_META_CMD_LOCK || metadata->op == BAM_META_CMD_UNLOCK) {
> +		if (!bdev->dev_data->bam_pipe_lock)
> +			return -EOPNOTSUPP;
> +
> +		/* Expecting a dummy write when locking, only one descriptor allowed. */
> +		if (async_desc->num_desc != 1)
> +			return -EINVAL;
> +	}
> +
> +	switch (metadata->op) {
> +	case BAM_META_CMD_LOCK:
> +		if (bchan->bam_locked)
> +			return -EBUSY;
> +
> +		hw_desc->flags |= DESC_FLAG_LOCK;

Why does this flag imply for the hardware.

I do not like the interface designed here. This is overloading. Can we
look at doing something better here.

-- 
~Vinod