Re: [igt-dev] [RFC 3/5] igt/lib: Add wrapper to check if gtt mapping is available

[Antonio Argenziano <antonio.argenziano@intel.com>]

On 21/02/19 11:49, Chris Wilson wrote:
> Quoting Antonio Argenziano (2019-02-21 19:27:43)
>> Add wrapper to get mmap_gtt version number and another to check if
>> gtt mapping is at all available.
>>
>> Cc: Katarzyna Dec <katarzyna.dec@intel.com>
>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> Cc: Matthew Auld <matthew.auld@intel.com>
>> Signed-off-by: Antonio Argenziano <antonio.argenziano@intel.com>
>> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
>> ---
>>   lib/ioctl_wrappers.c | 47 ++++++++++++++++++++++++++++++++++++--------
>>   lib/ioctl_wrappers.h | 11 +++++++++++
>>   2 files changed, 50 insertions(+), 8 deletions(-)
>>
>> diff --git a/lib/ioctl_wrappers.c b/lib/ioctl_wrappers.c
>> index d9b46088..25dd8ad3 100644
>> --- a/lib/ioctl_wrappers.c
>> +++ b/lib/ioctl_wrappers.c
>> @@ -659,6 +659,42 @@ static bool has_mmap_offset(int fd)
>>          return has_mmap_offset > 0;
>>   }
>>   
>> +/**
>> + * gem_mmap__gtt_version:
>> + * @fd: open i915 drm file descriptor
>> + *
>> + * This wraps I915_PARAM_MMAP_GTT_VERSION. It will return the supported feature
>> + * set for gtt mapping. Since the mappable aperture in not always present, this
>> + * function will return '-1' in case there is none.
>> + */
>> +static int gem_mmap__gtt_version(int fd)
>> +{
>> +       static int gtt_version = ~0;
>> +
>> +       if (gtt_version == ~0) {
>> +                       struct drm_i915_getparam gp;
>> +
>> +                       gtt_version = 0;
>> +
>> +                       memset(&gp, 0, sizeof(gp));
>> +                       gp.param = I915_PARAM_MMAP_GTT_VERSION;
>> +                       gp.value = &gtt_version;
>> +                       ioctl(fd, DRM_IOCTL_I915_GETPARAM, &gp);
>> +
>> +                       if(errno == -ENODEV)
>> +                               gtt_version = -1; /* No mappable aperture */
> 
> errno is only valid after a failed syscall.

Indeed, thanks for spotting this!

> 
> We the undersigned thoroughly dislike errno

Agreed, maybe another version value returned from the IOCTL or even a 
new PARAM_HAS_MMAP_GTT?

Antonio

> -Chris
> 
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