Re: [RFC PATCH 2/2] apple: dart: use driver specific instance of LMB

[Janne Grunau <j@jannau.net>]

On Tue, Oct 29, 2024 at 02:22:53PM +0530, Sughosh Ganu wrote:
> On Tue, 29 Oct 2024 at 14:02, Janne Grunau <j@jannau.net> wrote:
> >
> > On Tue, Oct 29, 2024 at 12:48:46PM +0530, Sughosh Ganu wrote:
> > > The LMB module is typically used for managing the platform's RAM
> > > memory. RAM memory gets added to the module's memory map, and
> > > subsequently allocated through various LMB API's.
> > >
> > > The IOMMU driver for the apple platforms also uses the LMB API's for
> > > allocating device virtual addresses(VA). These addresses are different
> > > from the RAM addresses, and cannot be added to the RAM memory map. Add
> > > a separate instance of LMB memory map for the device VA's, which gets
> > > managed by the IOMMU driver. Use lmb_push() and lmb_pop() functions to
> > > set-up the relevant lmb instance.
> >
> > thanks, this fixes the initial brokenness when setting up dma mappings
> > but I still see SError due to translation fault. I don't have time right
> > now to look into it so it could be unrelated to the iommu.
> 
> Good to know. Thanks for testing the changes.

It's SError-ing on `dc zva` of an invalid address which somehow got into
the main lmb. I don't see how but it went away with my minimal io_lmb
implemenmtation exposing lmb_setup, lmb_add, lmb_alloc, lmb_free.

I'm not too happy about this approach since it's a little fragile with
respect to the global struct lmb. to be somewhat safe we would need to
reorder lmb.c to avoid `static struct lmb lmb;` is visible in "shared"
code to avoid using it by surprise in the middle of functions like in
_lmb_alloc_base().

I'll post patches later today.

Janne