linux-kernel - Re: [PATCH v2 02/10] dmaengine: imx-sdma: fix spba-bus handling for i.MX8M

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Message-ID: <20250912084809.e6atdywisk4ywlr6@pengutronix.de>
Date: Fri, 12 Sep 2025 10:48:09 +0200
From: Marco Felsch <m.felsch@...gutronix.de>
To: Peng Fan <peng.fan@....nxp.com>
Cc: Vinod Koul <vkoul@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Jiada Wang <jiada_wang@...tor.com>, dmaengine@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/10] dmaengine: imx-sdma: fix spba-bus handling for
 i.MX8M

Hi Peng,

On 25-09-12, Peng Fan wrote:
> Hi Marco,
> 
> On Thu, Sep 11, 2025 at 11:56:43PM +0200, Marco Felsch wrote:
> >Starting with i.MX8M* devices there are multiple spba-busses so we can't
> >just search the whole DT for the first spba-bus match and take it.
> >Instead we need to check for each device to which bus it belongs and
> >setup the spba_{start,end}_addr accordingly per sdma_channel.
> 
> Could you please explain a bit why it is per sdma_channel, not per sdma_engine?

Well first, the sdma-slave/user defines which SPBA bus is used.
Furthermore not all users have to be part of the same SPBA bus or be
part of a SPBA bus at all. E.g. the i.mx8mm.dtsi sdma1 engine is used
by uart4 (not part of a SPBA bus) and uart1/2/3 (part of the
spba-bus@...00000).

I know that the use-case: "The SDMA engine can serve for multiple users
which are not part of the same SPBA bus" is not yet used but having the
code in place makes the driver more future proof.

Therefore I think having the SPBA addresses per user is correct.

Regards,
  Marco

> As I understand, all the channels belong to a sdma engine should use same
> spba_{start,end}_addr.
> 
> Thanks,
> Peng
>