[igt-dev] [RFC 5/5] igt/lib: If mappable aperture is missing return 0 size

[Chris Wilson]

Quoting Antonio Argenziano (2019-03-07 15:51:28)
> 
> 
> On 21/02/19 13:51, Chris Wilson wrote:
> > Quoting Antonio Argenziano (2019-02-21 21:45:46)
> >>
> >>
> >> On 21/02/19 12:01, Chris Wilson wrote:
> >>> Quoting Antonio Argenziano (2019-02-21 19:27:45)
> >>>> So far the aperture size has been read directly from the bar,
> >>>> in this patch we return zero if the mappable aperture is not available
> >>>> as the value stored in the bar might not be accurate. The patch also adds a
> >>>> 'require' when a call to gem_mappable_aperture_size() is made so that
> >>>> the aperture is guaranteed to exist before checking the size.
> >>>>
> >>>> Cc: Katarzyna Dec <katarzyna.dec at intel.com>
> >>>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >>>> Cc: Matthew Auld <matthew.auld at intel.com>
> >>>> Signed-off-by: Antonio Argenziano <antonio.argenziano at intel.com>
> >>>> ---
> >>>>    lib/ioctl_wrappers.c            | 28 +++++++++++++++++++---------
> >>>>    lib/ioctl_wrappers.h            |  2 +-
> >>>>    tests/i915/gem_concurrent_all.c | 12 ++++++------
> >>>>    tests/i915/gem_cpu_reloc.c      | 14 ++++++++++----
> >>>>    tests/i915/gem_mmap.c           |  4 ++--
> >>>>    tests/i915/gem_mmap_gtt.c       | 10 +++++-----
> >>>>    tests/i915/gem_pwrite.c         |  4 ++--
> >>>>    tests/i915/gem_shrink.c         |  2 +-
> >>>>    tests/i915/i915_pm_rpm.c        |  2 +-
> >>>>    tests/kms_flip.c                |  2 +-
> >>>>    tests/prime_mmap.c              |  7 +++++--
> >>>>    11 files changed, 53 insertions(+), 34 deletions(-)
> >>>>
> >>>> diff --git a/lib/ioctl_wrappers.c b/lib/ioctl_wrappers.c
> >>>> index 25dd8ad3..ab7c7a5e 100644
> >>>> --- a/lib/ioctl_wrappers.c
> >>>> +++ b/lib/ioctl_wrappers.c
> >>>> @@ -1440,19 +1440,14 @@ uint64_t gem_aperture_size(int fd)
> >>>>           return aperture_size;
> >>>>    }
> >>>>    
> >>>> -/**
> >>>> - * gem_mappable_aperture_size:
> >>>> - *
> >>>> - * Feature test macro to query the kernel for the mappable gpu aperture size.
> >>>> - * This is the area available for GTT memory mappings.
> >>>> - *
> >>>> - * Returns: The mappable gtt address space size.
> >>>> - */
> >>>> -uint64_t gem_mappable_aperture_size(void)
> >>>> +static uint64_t __gem_mappable_aperture_size(int fd)
> >>>>    {
> >>>>           struct pci_device *pci_dev = intel_get_pci_device();
> >>>>           int bar;
> >>>>    
> >>>> +       if (!gem_mmap__has_gtt(fd))
> >>>> +               return 0; /* Aperture not available */
> >>>> +
> >>>>           if (intel_gen(pci_dev->device_id) < 3)
> >>>>                   bar = 0;
> >>>
> >>> I swear we made this accessible via fd so that we didn't need root to
> >>> poke around libpciacess.
> >>
> >> mhh, couldn't find it. Is it in some IOCTL?
> > 
> > No, we extended get_aperture_ioctl to provide it, once upon a time. I
> > suggest we do something similar, or we use a param to get the actual
> > value. (Even if it's legacy, we can still justify a usecase as I'm
> > pretty sure 256MiB is hardcoded into several legacy userspaces.)
> 
> Is something like: https://paste.debian.net/1072096/ acceptable?

Yes.

Kernel->    old                   new
Userspace
   v

  old       no change             see old size, skips write

  new       reads 0               legacy HW gets mappable size
                                  new HW, 0?

So for new userspace, how do we determine 0 meaning old kernel, pick a
value for ourselves, or 0 meaning no aperture at all. PCI-ID? Or is it
simply that new userspace (that might run on no aperture devices)
doesn't care about the aperture size anyway, so it's a meaningless
question?
-Chris