linux-kernel - Re: [PATCH V10 1/1] dmaengine: amd: qdma: Add AMD QDMA driver

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Date: Wed, 17 Apr 2024 22:33:24 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Lizhi Hou <lizhi.hou@....com>
Cc: dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	Nishad Saraf <nishads@....com>, nishad.saraf@....com,
	sonal.santan@....com, max.zhen@....com
Subject: Re: [PATCH V10 1/1] dmaengine: amd: qdma: Add AMD QDMA driver

On 08-04-24, 11:06, Lizhi Hou wrote:

> > > +static void *qdma_get_metadata_ptr(struct dma_async_tx_descriptor *tx,
> > > +				   size_t *payload_len, size_t *max_len)
> > > +{
> > > +	struct qdma_mm_vdesc *vdesc;
> > > +
> > > +	vdesc = container_of(tx, typeof(*vdesc), vdesc.tx);
> > > +	if (payload_len)
> > > +		*payload_len = sizeof(vdesc->dev_addr);
> > > +	if (max_len)
> > > +		*max_len = sizeof(vdesc->dev_addr);
> > > +
> > > +	return &vdesc->dev_addr;
> > Can you describe what metadata is being used here for?
> 
> The metadata is the device address the dma request will transfer
> 
> data to / from.  Please see the example usage here:
> 
> https://github.com/houlz0507/XRT-1/blob/qdma_v1_usage/src/runtime_src/core/pcie/driver/linux/xocl/subdev/qdma.c#L311
> 
> Before dmaengine_submit(), it specifies the device address.

Hmmm, why is the vaddr passed like this, why not use slave_config for
this

-- 
~Vinod