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

Vinod Koul
2024-04-18T17:08:25Z

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

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

--
~Vinod