Re: [PATCH v9 09/38] dma: cirrus: Convert to DT for Cirrus EP93xx

Alexander Sverdlin
2024-03-28T07:21:59Z

Hello Vinod!

On Thu, 2024-03-28 at 10:01 +0530, Vinod Koul wrote:
> On 26-03-24, 12:18, Nikita Shubin via B4 Relay wrote:
> > From: Nikita Shubin <nikita.shubin@maquefel.me>
> >
> > Convert Cirrus EP93xx DMA to device tree usage:
>
> Subsytem is dmaengine: pls fix that
>
> >
> > - add OF ID match table with data
> > - add of_probe for device tree
> > - add xlate for m2m/m2p
> > - drop subsys_initcall code
> > - drop platform probe
> > - drop platform structs usage
> >
> > > From now on it only supports device tree probing.
> >
> > Co-developed-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
> > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
> > Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
> > ---
> >   drivers/dma/ep93xx_dma.c                 | 239 ++++++++++++++++++++++++-------
> >   include/linux/platform_data/dma-ep93xx.h |   6 +
> >   2 files changed, 191 insertions(+), 54 deletions(-)
> >
> > diff --git a/drivers/dma/ep93xx_dma.c b/drivers/dma/ep93xx_dma.c
> > index d6c60635e90d..17c8e2badee2 100644
> > --- a/drivers/dma/ep93xx_dma.c
> > +++ b/drivers/dma/ep93xx_dma.c

[...]

> >
> > @@ -104,6 +106,11 @@
> >   #define DMA_MAX_CHAN_BYTES 0xffff
> >   #define DMA_MAX_CHAN_DESCRIPTORS 32
> >
> > +enum ep93xx_dma_type {
> > + M2P_DMA,
>
> Is this missing P2M?

Not really. It's not the most obvious one, but anyway a way to enumerate
two types of DMA engines:

"7.1.1 DMA Features List
DMA specific features are:
• Ten fully independent, programmable DMA controller internal M2P/P2M
channels (5 Tx and 5 Rx).
• Two dedicated channels for Memory-to-Memory (M2M) and
Memory-to-External Peripheral Transfers (external M2P/P2M)."

Now the confusing part is that this "M2M" engine is actually used
to transfer to and from *some* devices, like SPI and IDE.
So both engines are capable of M2P and P2M, maybe Cirrus has named
two engines in a sub-optimal way decades ago and this is now a bit
historical naming.

> > + M2M_DMA,
> > +};

--
Alexander Sverdlin.