On Wed, 06 Mar 2024, Jani Nikula <jani.nikula@xxxxxxxxx> wrote:
> Long term goal: Separate display code from struct drm_i915_private and
> i915_drv.h, and everything in them. Ditto for xe.
>
> First step, draft some ideas how we could use struct intel_display as
> the main device structure for display, while struct drm_device remains
> in struct drm_i915_private (or, in the case of xe, in struct xe_device).
>
> To get at struct drm_device * given a struct intel_display *, simply
> store a backpointer.
>
> To get at struct intel_display * given a struct drm_device *, require
> storing a struct intel_display * right after struct drm_device in
> memory. It's slightly hackish, but devm_drm_dev_alloc() facilitates
> defining the enclosing struct as we wish.
To emphasize, getting from struct drm_device * to struct intel_display *
is the biggest problem this solves.
We have a lot of drm hooks that have a drm device/connector/encoder/etc
parameter and no additional context. We can always get from other
objects to the drm device, but how to get from that to intel_display?
We don't want to know the definitions of struct drm_i915_private or
struct xe_device within display code. We don't want to have a function
call to i915 or xe cores to translate drm device to intel_display.
> A shared named struct for this would be nice, but that would require
> changing all the i915->drm and xe->drm dereferences. The use of an
> unnamed __packed struct avoids that.
To elaborate, this means
struct foo {
struct drm_device drm;
struct intel_display *__intel_display_private;
};
struct drm_i915_private {
struct foo bar;
/* ... */
};
So display code could use container_of to get from struct drm device to
struct foo, and thus __intel_display_private. However, *all* of i915 and
xe core code would have to be modified to fix i915->drm references to
i915->bar.drm. Not cool.
BR,
Jani.
>
> Users are added in follow-up patches; the patches may be squashed
> together before final submission.
>
> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_display_core.h | 3 +++
> .../gpu/drm/i915/display/intel_display_device.c | 13 +++++++++++++
> drivers/gpu/drm/i915/i915_drv.h | 11 ++++++++++-
> drivers/gpu/drm/xe/xe_device_types.h | 15 +++++++++++++--
> 4 files changed, 39 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_core.h b/drivers/gpu/drm/i915/display/intel_display_core.h
> index 2167dbee5eea..85b542bb45e6 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_core.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_core.h
> @@ -282,6 +282,9 @@ struct intel_wm {
> };
>
> struct intel_display {
> + /* drm device backpointer */
> + struct drm_device *drm;
> +
> /* Display functions */
> struct {
> /* Top level crtc-ish functions */
> diff --git a/drivers/gpu/drm/i915/display/intel_display_device.c b/drivers/gpu/drm/i915/display/intel_display_device.c
> index c02d79b50006..63de9917e346 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_device.c
> +++ b/drivers/gpu/drm/i915/display/intel_display_device.c
> @@ -922,6 +922,19 @@ void intel_display_device_probe(struct drm_i915_private *i915)
> const struct intel_display_device_info *info;
> u16 ver, rel, step;
>
> + /*
> + * These are here for now to do them as early as possible. i915 has just
> + * been allocated, drm isn't even initialized yet, but we have the
> + * pointer.
> + *
> + * Later on, the display probe would allocate struct intel_display
> + * itself, and return the pointer to the caller, for whom struct
> + * intel_display would be an opaque type, a cookie to be passed on to
> + * display functions.
> + */
> + i915->__intel_display_private = &i915->display;
> + i915->display.drm = &i915->drm;
> +
> if (HAS_GMD_ID(i915))
> info = probe_gmdid_display(i915, &ver, &rel, &step);
> else
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index e81b3b2858ac..2e80afbe7a4e 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -185,7 +185,16 @@ struct i915_selftest_stash {
> };
>
> struct drm_i915_private {
> - struct drm_device drm;
> + struct {
> + struct drm_device drm;
> +
> + /*
> + * Display private data. Do *not* access directly. Must be
> + * placed right after drm_device to facilitate getting to it
> + * given a drm device pointer.
> + */
> + struct intel_display *__intel_display_private;
> + } __packed;
>
> struct intel_display display;
>
> diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
> index 9785eef2e5a4..0347fbc925c9 100644
> --- a/drivers/gpu/drm/xe/xe_device_types.h
> +++ b/drivers/gpu/drm/xe/xe_device_types.h
> @@ -210,8 +210,19 @@ struct xe_tile {
> * struct xe_device - Top level struct of XE device
> */
> struct xe_device {
> - /** @drm: drm device */
> - struct drm_device drm;
> + struct {
> + /** @drm: drm device */
> + struct drm_device drm;
> +
> +#if IS_ENABLED(CONFIG_DRM_XE_DISPLAY)
> + /**
> + * @__intel_display_private: Display private data. Do *not*
> + * access directly. Must be placed right after drm_device to
> + * facilitate getting to it given a drm device pointer.
> + */
> + struct intel_display *__intel_display_private;
> +#endif
> + } __packed;
>
> /** @devcoredump: device coredump */
> struct xe_devcoredump devcoredump;
--
Jani Nikula, Intel
