Re: [RFC v1 1/1] Refactor ACPI DMA to support platforms without shared info descriptor in CSRT

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On Wed, Mar 22, 2023 at 11:34:40AM +0200, Andy Shevchenko wrote:
> On Wed, Mar 22, 2023 at 07:56:11AM +0000, Niyas Sait wrote:
> > On 21/03/2023 17:53, Andy Shevchenko wrote:
> > 
> > > can_we_avoid_long_name_of_the_functions_please() ?
> > 
> > Sure, will do that.
> > 
> > > Also is this renaming is a must?
> > 
> > It is not a must. I considered the existing method with shared info
> > as a special case as it uses non standard descriptors from CSRT table
> > and introduced the new function to handle it.
> > 
> > > Btw, what is the real argument of not using this table?
> > > 
> > > Yes, I know that this is an MS extension, but why ARM needs something else and
> > > why even that is needed at all? CSRT is only for the _shared_ DMA resources
> > > and I think most of the IPs nowadays are using private DMA engines (or
> > > semi-private when driver based on ID can know which channel services which
> > > device).
> > 
> > The issue is that shared info descriptor is not part of CSRT definition [1]
> > and I think it is not standardized or documented anywhere.
> > 
> > I was specifically looking at NXP I.MX8MP platform and the DMA lines for
> > devices are specified using FixedDMA resource descriptor. I think other Arm
> > platforms like RPi have similar requirement.
> 
> Perhaps, but my question is _why_ is it so?
> I.o.w. what is the technical background for this solution.
> 
> > [1] https://uefi.org/sites/default/files/resources/CSRT%20v2.pdf

JFYI: ARM platform(s) use SPCR, which is also not a part of the specification.

-- 
With Best Regards,
Andy Shevchenko





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