RE: [PATCH RESEND v4 2/2] dmaengine: dw-edma: Add non-LL mode

[Verma, Devendra]

[AMD Official Use Only - AMD Internal Distribution Only]

Thank you Manivannan for reviewing the patches!
Please check my response inline.

Regards,
Devendra

> -----Original Message-----
> From: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> Sent: Monday, October 27, 2025 6:45 PM
> To: Verma, Devendra <Devendra.Verma@xxxxxxx>
> Cc: bhelgaas@xxxxxxxxxx; vkoul@xxxxxxxxxx; dmaengine@xxxxxxxxxxxxxxx;
> linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Simek, Michal
> <michal.simek@xxxxxxx>
> Subject: Re: [PATCH RESEND v4 2/2] dmaengine: dw-edma: Add non-LL mode
>
> Caution: This message originated from an External Source. Use proper
> caution when opening attachments, clicking links, or responding.
>
>
> On Tue, Oct 14, 2025 at 05:46:34PM +0530, Devendra K Verma wrote:
> > AMD MDB IP supports Linked List (LL) mode as well as non-LL mode.
>
> Isn't the patch adding non-LL mode for all platforms, not just for AMD?
>

A specific case where LL mode is enabled, which is the default mode, in
this case all the IPs can support the non-LL mode provided it shall be
configured via the config param peripheral_config by the client.
The default case where non-LL mode is enabled for all the IPs is NOT
supported by all the IPs.

> > The current code does not have the mechanisms to enable the DMA
> > transactions using the non-LL mode. The following two cases are added
> > with this patch:
> > - When a valid physical base address is not configured via the
> >   Xilinx VSEC capability then the IP can still be used in non-LL
> >   mode. The default mode for all the DMA transactions and for all
> >   the DMA channels then is non-LL mode.
> > - When a valid physical base address is configured but the client
> >   wants to use the non-LL mode for DMA transactions then also the
> >   flexibility is provided via the peripheral_config struct member of
> >   dma_slave_config. In this case the channels can be individually
> >   configured in non-LL mode. This use case is desirable for single
> >   DMA transfer of a chunk, this saves the effort of preparing the
> >   Link List.
> >
> > Signed-off-by: Devendra K Verma <devendra.verma@xxxxxxx>
> > ---
> > Changes in v4
> >   No change
> >
> > Changes in v3
> >   No change
> >
> > Changes in v2
> >   Reverted the function return type to u64 for
> >   dw_edma_get_phys_addr().
> >
> > Changes in v1
> >   Changed the function return type for dw_edma_get_phys_addr().
> >   Corrected the typo raised in review.
> > ---
> >  drivers/dma/dw-edma/dw-edma-core.c    | 38 ++++++++++++++++++---
> >  drivers/dma/dw-edma/dw-edma-core.h    |  1 +
> >  drivers/dma/dw-edma/dw-edma-pcie.c    | 44 +++++++++++++++++--------
> >  drivers/dma/dw-edma/dw-hdma-v0-core.c | 62
> ++++++++++++++++++++++++++++++++++-
> >  include/linux/dma/edma.h              |  1 +
> >  5 files changed, 127 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/dma/dw-edma/dw-edma-core.c
> > b/drivers/dma/dw-edma/dw-edma-core.c
> > index b43255f..3283ac5 100644
> > --- a/drivers/dma/dw-edma/dw-edma-core.c
> > +++ b/drivers/dma/dw-edma/dw-edma-core.c
> > @@ -223,8 +223,28 @@ static int dw_edma_device_config(struct
> dma_chan *dchan,
> >                                struct dma_slave_config *config)  {
> >       struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
> > +     int nollp = 0;
>
> s/nollp/non_ll
>

Suggestion accepted. Thanks!

> > +
> > +     if (WARN_ON(config->peripheral_config &&
> > +                 config->peripheral_size != sizeof(int)))
>
> Use proper dev_err(), not WARN_ON.
>

Suggestion accepted, dev_err() replaces WARN_ON() in latest drop.
Thanks!

> > +             return -EINVAL;
> >
> >       memcpy(&chan->config, config, sizeof(*config));
> > +
> > +     /*
> > +      * When there is no valid LLP base address available
> > +      * then the default DMA ops will use the non-LL mode.
> > +      * Cases where LL mode is enabled and client wants
> > +      * to use the non-LL mode then also client can do
> > +      * so via providing the peripheral_config param.
>
> Make use of 80 columns for comments throughout this patch.
>

Comments follow the 80-column guideline. Thanks!

> Rest LGTM!
>
> - Mani
>
> --
> மணிவண்ணன் சதாசிவம்