[igt-dev] [i-g-t] lib/i915: Use FIXED mapping only for discrete memory

[Surendrakumar Upadhyay, TejaskumarX]

> -----Original Message-----
> From: Latvala, Petri <petri.latvala at intel.com>
> Sent: 30 August 2021 14:07
> To: Surendrakumar Upadhyay, TejaskumarX
> <tejaskumarx.surendrakumar.upadhyay at intel.com>
> Cc: igt-dev at lists.freedesktop.org
> Subject: Re: [igt-dev] [i-g-t] lib/i915: Use FIXED mapping only for discrete
> memory
> 
> On Fri, Aug 27, 2021 at 06:30:02PM +0530, Tejas Upadhyay wrote:
> > The FIXED mapping is only used for discrete, and mapping type is
> > pre-defined. This disables the other type of mmap offsets when
> > discrete memory is used.
> >
> > Taken from kernel commit:
> > commit 7961c5b60f23 ("drm/i915: Add TTM offset argument to mmap.")
> >
> > Signed-off-by: Tejas Upadhyay
> > <tejaskumarx.surendrakumar.upadhyay at intel.com>
> > ---
> >  include/drm-uapi/i915_drm.h | 1 +
> >  lib/i915/gem_mman.c         | 8 +++++++-
> >  2 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/drm-uapi/i915_drm.h b/include/drm-uapi/i915_drm.h
> > index a1c0030c..b46367f2 100644
> > --- a/include/drm-uapi/i915_drm.h
> > +++ b/include/drm-uapi/i915_drm.h
> > @@ -871,6 +871,7 @@ struct drm_i915_gem_mmap_offset {  #define
> > I915_MMAP_OFFSET_WC  1  #define I915_MMAP_OFFSET_WB  2  #define
> > I915_MMAP_OFFSET_UC  3
> > +#define I915_MMAP_OFFSET_FIXED 4
> >
> >  	/*
> >  	 * Zero-terminated chain of extensions.
> > diff --git a/lib/i915/gem_mman.c b/lib/i915/gem_mman.c index
> > 0406a0b9..1917c24d 100644
> > --- a/lib/i915/gem_mman.c
> > +++ b/lib/i915/gem_mman.c
> > @@ -75,7 +75,13 @@ bool gem_has_legacy_mmap(int fd)
> >
> >  bool gem_has_mmap_offset_type(int fd, const struct mmap_offset *t)  {
> > -	return gem_has_mmap_offset(fd) || t->type ==
> I915_MMAP_OFFSET_GTT;
> > +	if (gem_has_mmap_offset(fd))
> > +		if (!gem_has_lmem(fd))
> > +			return !(t->type == I915_MMAP_OFFSET_FIXED);
> > +		else
> > +			return !(t->type != I915_MMAP_OFFSET_FIXED);
> 
> Why the !(a == b) stuff?
>        ^^^

If its discrete memory and offset type is fixed then only its valid combination.  Reverse if not discrete then any offset type except fixed is valid combination.

Thanks,
Tejas 
> 
> 
> --
> Petri Latvala