Re: [PATCH 08/11] dmaengine: cppi41: Implement the glue for da8xx

[Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>]

* Alexandre Bailon <abailon-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> [170110 07:23]:
> On 01/10/2017 11:05 AM, Sekhar Nori wrote:
> > On DA8xx, CPPI 4.1 DMAengine is not an independent system resource, but
> > embedded within the USB 2.0 controller. So, I think all that is needed
> > is for MUSB DA8xx glue to trigger probe of CPPI 4.1 dmaengine driver
> > when it is ready. I am not sure all this DA850-specific clock handling
> > is really necessary.
> Actually, we have a circular dependency.
> USB core tries to get DMA channels during the probe, which fails because
> CPPI 4.1 driver is not ready.
> But it will never be ready because the USB clock must be enabled before
> DMA driver probe, what will not happen because USB driver have disabled
> the clock when probe failed.
> 
> Someone in the office suggested me to use the component API,
> that could help me to probe the DMA from the USB probe.
> 
> Another way to workaround the dependency would be to do defer the
> function calls that access to hardware to avoid to control clock from
> DMA driver.

Or you really have some wrapper IP block around musb and cppi41 just
like am335x has.

See drivers/usb/musb/musb_am335x.c and compatible properties for
"ti,am33xx-usb" and it's children in am33xx.dtsi.

Regards,

Tony
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