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

[Lizhi Hou]

On 4/18/24 10:08, Vinod Koul wrote:
> On 17-04-24, 10:53, Lizhi Hou wrote:
> > On 4/17/24 10:03, Vinod Koul wrote:
> > > 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
> > This is because the hardware is capable to process multiple vdesc at one
> > kick off.
> >
> > For example, there are two pending vdesc: vd1 and vd2. If there is enough
> > free
> >
> > space in hardware queue, the vd1 and vd2 can be put in queue, and do one
> > kick off
> >
> > to transfer both vd1 and vd2.
> >
> > The destination device address of vd1 and vd2 could be any valid device
> > address.
> >
> > desc_metadata_ptr seems helpful for the per vdesc destination device
> > address.
> >
> >
> > If using slave_config, it needs to call dmaengine_slave_config() and
> That would be the right thing to do...
>
> - set parameters and call dmaengine_slave_config()
> - prep transfer for vd1 dmaengine_prep_slave_sg()
> - set parameters and call dmaengine_slave_config()
> - prep transfer for vd2 dmaengine_prep_slave_sg()
> - submit vd1
> - submit vd2
> - issue_pending
>          - you see you can issue both as you have space, so do that
>
> This should be done always to maximize the dmaengine thoroughput

Thanks for your comments. I will change this.


Lizhi

> > dmaengine_prep_slave_sg() with a lock protection. Is this what you would
> > recommend?
> >
> >
> > Thanks,
> >
> > Lizhi