linux-kernel - Re: [PATCH v3 01/11] dmaengine: Add hw_id to dma_slave

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Message-ID: <aYOgV-dmeA8XjNyw@lizhi-Precision-Tower-5810>
Date: Wed, 4 Feb 2026 14:39:03 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: vkoul@...nel.org, mani@...nel.org, jingoohan1@...il.com,
	lpieralisi@...nel.org, kwilczynski@...nel.org, robh@...nel.org,
	bhelgaas@...gle.com, dmaengine@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/11] dmaengine: Add hw_id to dma_slave_caps

On Wed, Feb 04, 2026 at 11:54:29PM +0900, Koichiro Den wrote:
> Remote DMA users may need to map or otherwise correlate DMA resources on
> a per-hardware-channel basis (e.g. DWC EP eDMA linked-list windows).
> However, struct dma_chan does not expose a provider-defined hardware
> channel identifier.
>
> Add an optional dma_slave_caps.hw_id field to allow DMA engine drivers
> to report a provider-specific hardware channel identifier to clients.
> Initialize the field to -1 in dma_get_slave_caps() so drivers that do
> not populate it continue to behave as before.
>
> Signed-off-by: Koichiro Den <den@...inux.co.jp>
> ---
>  drivers/dma/dmaengine.c   | 1 +
>  include/linux/dmaengine.h | 2 ++
>  2 files changed, 3 insertions(+)
>
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index ca13cd39330b..b544eb99359d 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -603,6 +603,7 @@ int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
>  	caps->cmd_pause = !!device->device_pause;
>  	caps->cmd_resume = !!device->device_resume;
>  	caps->cmd_terminate = !!device->device_terminate_all;
> +	caps->hw_id = -1;
>
>  	/*
>  	 * DMA engine device might be configured with non-uniformly
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 99efe2b9b4ea..71bc2674567f 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -507,6 +507,7 @@ enum dma_residue_granularity {
>   * @residue_granularity: granularity of the reported transfer residue
>   * @descriptor_reuse: if a descriptor can be reused by client and
>   * resubmitted multiple times
> + * @hw_id: provider-specific hardware channel identifier (-1 if unknown)
>   */
>  struct dma_slave_caps {
>  	u32 src_addr_widths;
> @@ -520,6 +521,7 @@ struct dma_slave_caps {
>  	bool cmd_terminate;
>  	enum dma_residue_granularity residue_granularity;
>  	bool descriptor_reuse;
> +	int hw_id;

I have not see where use it? Does src_id of struct dma_chan work?

Frank

>  };
>
>  static inline const char *dma_chan_name(struct dma_chan *chan)
> --
> 2.51.0
>