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Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: Add support for ASPEED i2Cv2
From: Jeremy Kerr <jk@codeconstruct.com.au>
To: Ryan Chen <ryan_chen@aspeedtech.com>, Rob Herring <robh+dt@kernel.org>, 
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Date: Wed, 22 Feb 2023 09:30:14 +0800
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Hi Ryan,

> > On the other hand, if it's just because of OS behaviour, then this
> > doesn't belong
> > in the DT.
> >=20
> > Maybe to help us understand: why would you ever *not* want DMA
> > mode?
> > Isn't that always preferable?
> In AST SOC i2c design is 16 i2c bus share one dma engine.=20

Does this mean that only one i2c controller in the system can be
configured to use DMA? Or is it able to be shared between multiple
controllers?

> It can be switch setting by dts setting. Otherwise driver by default
> probe is DMA mode.

You've explained what the modes do, and how they're switched, and what
the default is. However this doesn't explain *why* someone would want
to choose a particular mode when creating a controller node.

Still with the question above: assuming there are no restrictions on
DMA usage, why wouldn't a driver implementation just enable it always?

Cheers,


Jeremy