Re: [PATCH i-g-t v4] lib/i915/gem_mman: Add a helper for obtaining MMAP_GTT interface version

[Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>]

Quoting Janusz Krzysztofik (2019-05-31 10:29:16)
> From: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxx>
> 
> If a test calls a function which depends on availability of a specific
> version of MMAP_GTT interface, an error may occur on unsupported hardware.
> That may negatively affect results reported by a test framework even if
> that test ignores the failure and succeedes.
> 
> This helper wraps up an IOCTL call which returns a version number of
> MMAP_GTT interface.  It may be used by tests which should adjust their
> scope depending on availability of a specific version of MMAP_GTT
> interface.
> 
> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxx>
> Cc: Antonio Argenziano <antonio.argenziano@xxxxxxxxx>
> Cc: Michal Wajdeczko <michal.wajdeczko@xxxxxxxxx>
> ---
> Changelog:
> v3 -> v4:
> - return errno value on failure (Chris - thanks!),
> - clear errno before return, as other helpers do,
> - reword the helper documentation and commit message again (Chris -
>   thanks!).
> 
> v2 (internal) -> v3:
> - make the code less obsucre, more explicit (Antonio - thanks!),
> - reword the helper documentation and commit message.
> 
> v1 (internal) -> v2 (internal):
> - minimize future potential conflicts with 
>   https://patchwork.freedesktop.org/patch/294053/?series=58551&rev=1
>   (no progress with than one so not waiting for it any longer):
>   - convert the helper to a drop-in replacement of the one from the
>     above mentioned patch, returning mappable aperture version, not
>     only information on its availability,
>   - drop any other wrappers,
> - document the helper,
> - reword commit message.
> 
>  lib/i915/gem_mman.c | 25 +++++++++++++++++++++++++
>  lib/i915/gem_mman.h |  1 +
>  2 files changed, 26 insertions(+)
> 
> diff --git a/lib/i915/gem_mman.c b/lib/i915/gem_mman.c
> index 3cf9a6bb..2c3d6971 100644
> --- a/lib/i915/gem_mman.c
> +++ b/lib/i915/gem_mman.c
> @@ -40,6 +40,31 @@
>  #define VG(x) do {} while (0)
>  #endif
>  
> +/**
> + * gem_mmap__gtt_version:
> + * @fd: open i915 drm file descriptor
> + *
> + * This functions wraps up an IOCTL to obtain MMAP_GTT interface version
> + *
> + * Returns: MMAP_GTT interface version, kernel error code on failure.
> + */
> +int gem_mmap__gtt_version(int fd)
> +{
> +       int gtt_version, ret;
> +       struct drm_i915_getparam gp = {
> +               .param = I915_PARAM_MMAP_GTT_VERSION,
> +               .value = &gtt_version,
> +       };
> +
> +       if (ioctl(fd, DRM_IOCTL_I915_GETPARAM, &gp))
> +               ret = errno;

ret = -errno; :)

Petri also like it when we then say igt_assume(ret);

Or one could use

{
	int result = -EIO;
	struct ... gp = {
		.param = I915_PARAM_MMAP_GTT_VERSION,
		.value = &result,
	};

	if (ioctl(fd, DRM_IOCTL_I915_GETPARAM, &gp)) {
		result = -errno;
		igt_assume(result);
	}

	errno = 0;
	return result;
}

Now just put it to use somewhere.
-Chris
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