On Wed, Mar 22, 2023 at 12:00:36PM +0000, Niyas Sait wrote: > On 22/03/2023 09:34, Andy Shevchenko wrote: ... > > > > 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. > > > > NXP I.MX8MP board uses shared DMA controller and the current ACPI firmware > describes DMA request lines for devices using ACPI FixedDMA descriptors. > > > JFYI: ARM platform(s) use SPCR, which is also not a part of the specification. > > SPCR and CSRT tables have permissive licensing and probably okay to use > them. > > The main issue is that the shared info descriptor in the CSRT table is not a > standard and none of the arm platforms uses them. SPCR is not standard either. So, that's to show that this is not an argument. Are those firmwares already in the wild? Why they can't be fixed and why existing CSRT shared info data structure can't be used. > >> [1]https://uefi.org/sites/default/files/resources/CSRT%20v2.pdf -- With Best Regards, Andy Shevchenko
