RE: [PATCH v28 2/4] dt-bindings: i2c: ast2600-i2c.yaml: Add global-regs and enable-dma properties

> > Subject: Re: [PATCH v28 2/4] dt-bindings: i2c: ast2600-i2c.yaml: Add
> > global-regs and enable-dma properties
> >
> > Hi Ryan,
> >
> > > > Sounds reasonable, but before you do so, how are you planning to
> > > > manage the allocation of DMA channels across multiple i2c peripherals?
> > > >
> > > The AST2600 I2C hardware has only one can use DMA at a time.
> > > To avoid the complexity of managing DMA channel contention, I plan
> > > to use buffer mode by default for all controllers, which still
> > > provides better performance than byte mode without requiring DMA
> > > channel
> > allocation.
> >
> > OK, but your wording there ("by default") implies that DMA is still
> > selectable for one controller peripheral. In which case: you still
> > have the problem of managing DMA channel contention, but now it's at
> runtime instead.
> >
> > So my question still stands: how are you planning to enforce that DMA
> > is only enabled for one controller?
> >
> > Or are you planning to disable I2C DMA entirely on AST2600?
> Yes, This is my intent to do.
> Disable I2C DMA entirely on AST2600.
> If I remove DMA, should can I keep byte and buffer for sysfs?

Hello Rob,

On the AST2600, we have a single-channel constraint, which makes DMA
support across all controllers difficult to implement without some kind of
predefined configuration. That would be a bit of a misuse of a DT property.

For future platforms such as the AST2700, DMA support should be much
more straightforward. DMA capability can be inferred from the compatible
string.

Unless there are any objections, I will rework this series to use buffer mode
only on the AST2600, and add AST2700 DMA support separately.

Ryan