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

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Date: Thu, 28 Mar 2024 08:21:32 +0100
From: Alexander Sverdlin <alexander.sverdlin@...il.com>
To: Vinod Koul <vkoul@...nel.org>, nikita.shubin@...uefel.me
Cc: dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org, Arnd Bergmann
	 <arnd@...db.de>
Subject: Re: [PATCH v9 09/38] dma: cirrus: Convert to DT for Cirrus EP93xx

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@...uefel.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@...il.com>
> > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...il.com>
> > Signed-off-by: Nikita Shubin <nikita.shubin@...uefel.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.