Re: [PATCH i-g-t 1/8] lib/igt_kms: Drop the ioctl fallback for CRTC id to pipe mapping

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Jan 27, 2026 at 01:55:58PM +0200, Jani Nikula wrote:
> The kernel support for i915_pipe debugfs has been around for 2½ years in
> both i915 and xe. Drop the ioctl fallback for simplicity. Rename the
> function __intel_get_pipe_from_crtc_index() as it's now purely about
> CRTC index and not id.

I was actaully pondering about using the ioctl as a hint to the
kernel whether userspace is using MI_WAIT_SCANLINE, and if not
I could start using the scanline window wait stuff for the
vblank evasion in the driver (which might be nice for some pfit
shenanigans). I gave up on that after realizing that igt was also
using the ioctl. So getting rid of the ioctl use here migth
actually be a good thing for me, and it means we just have one
codepath to deal with for both kernel drivers.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> 
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  lib/igt_kms.c | 47 ++++++++++-------------------------------------
>  1 file changed, 10 insertions(+), 37 deletions(-)
> 
> diff --git a/lib/igt_kms.c b/lib/igt_kms.c
> index bd02148d1d3f..a236597ac152 100644
> --- a/lib/igt_kms.c
> +++ b/lib/igt_kms.c
> @@ -1316,51 +1316,27 @@ void kmstest_dump_mode(drmModeModeInfo *mode)
>  }
>  
>  /*
> - * With non-contiguous pipes display, crtc mapping is not always same
> - * as pipe mapping, In i915 pipe is enum id of i915's crtc object.
> - * hence allocating upper bound igt_pipe array to support non-contiguos
> - * pipe display and reading pipe enum for a crtc using GET_PIPE_FROM_CRTC_ID
> - * ioctl for a pipe to do pipe ordering with respect to crtc list.
> + * The hardware pipe may be different from the CRTC index. Figure out the CRTC
> + * index to pipe mapping from the debugfs.
>   */
> -static int __intel_get_pipe_from_crtc_id(int fd, int crtc_id, int crtc_idx)
> +static int __intel_get_pipe_from_crtc_index(int fd, int crtc_index)
>  {
>  	char buf[2];
>  	int debugfs_fd, res = 0;
> +	char pipe_char;
>  
> -	/*
> -	 * No GET_PIPE_FROM_CRTC_ID ioctl support for XE. Instead read
> -	 * from the debugfs "i915_pipe".
> -	 *
> -	 * This debugfs is applicable for both i915 & XE. For i915, still
> -	 * we can fallback to ioctl method to support older kernels.
> -	 */
> -	debugfs_fd = igt_debugfs_pipe_dir(fd, crtc_idx, O_RDONLY);
> +	debugfs_fd = igt_debugfs_pipe_dir(fd, crtc_index, O_RDONLY);
>  
>  	if (debugfs_fd >= 0) {
>  		res = igt_debugfs_simple_read(debugfs_fd, "i915_pipe", buf, sizeof(buf));
>  		close(debugfs_fd);
>  	}
>  
> -	if (res <= 0) {
> -		/* Fallback to older ioctl method. */
> -		if (is_i915_device(fd)) {
> -			struct drm_i915_get_pipe_from_crtc_id get_pipe;
> -
> -			get_pipe.pipe = 0;
> -			get_pipe.crtc_id =  crtc_id;
> +	igt_assert_f(res > 0, "Failed to read the debugfs i915_pipe.\n");
>  
> -			do_ioctl(fd, DRM_IOCTL_I915_GET_PIPE_FROM_CRTC_ID,
> -				 &get_pipe);
> +	igt_assert_eq(sscanf(buf, "%c", &pipe_char), 1);
>  
> -			return get_pipe.pipe;
> -		} else
> -			igt_assert_f(false, "XE: Failed to read the debugfs i915_pipe.\n");
> -	} else {
> -		char pipe;
> -
> -		igt_assert_eq(sscanf(buf, "%c", &pipe), 1);
> -		return kmstest_pipe_to_index(pipe);
> -	}
> +	return kmstest_pipe_to_index(pipe_char);
>  }
>  
>  /**
> @@ -1395,8 +1371,7 @@ int kmstest_get_pipe_from_crtc_id(int fd, int crtc_id)
>  
>  	drmModeFreeResources(res);
>  
> -	return is_intel_device(fd) ?
> -		__intel_get_pipe_from_crtc_id(fd, crtc_id, i) : i;
> +	return is_intel_device(fd) ? __intel_get_pipe_from_crtc_index(fd, i) : i;
>  }
>  
>  /**
> @@ -3231,9 +3206,7 @@ void igt_display_require(igt_display_t *display, int drm_fd)
>  
>  	for (i = 0; i < resources->count_crtcs; i++) {
>  		igt_crtc_t *crtc;
> -		int pipe_enum = (is_intel_dev)?
> -			__intel_get_pipe_from_crtc_id(drm_fd,
> -						      resources->crtcs[i], i) : i;
> +		int pipe_enum = is_intel_dev ? __intel_get_pipe_from_crtc_index(drm_fd, i) : i;
>  
>  		crtc = igt_crtc_for_pipe(display, pipe_enum);
>  		crtc->pipe = pipe_enum;
> -- 
> 2.47.3

-- 
Ville Syrjälä
Intel