On Thu, Jul 15, 2021 at 09:49:51PM +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> Quite a few places are hand rolling the modeset lock backoff dance.
> Let's suck that into a helper macro that is easier to use without
> forgetting some steps.
>
> The main downside is probably that the implementation of
> drm_with_modeset_lock_ctx() is a bit harder to read than a hand
> rolled version on account of being split across three functions,
> but the actual code using it ends up being much simpler.
>
> Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_modeset_lock.c | 44 ++++++++++++++++++++++++++++++
> include/drm/drm_modeset_lock.h | 20 ++++++++++++++
> 2 files changed, 64 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
> index fcfe1a03c4a1..083df96632e8 100644
> --- a/drivers/gpu/drm/drm_modeset_lock.c
> +++ b/drivers/gpu/drm/drm_modeset_lock.c
> @@ -425,3 +425,47 @@ int drm_modeset_lock_all_ctx(struct drm_device *dev,
> return 0;
> }
> EXPORT_SYMBOL(drm_modeset_lock_all_ctx);
> +
> +void _drm_modeset_lock_begin(struct drm_modeset_acquire_ctx *ctx,
> + struct drm_atomic_state *state,
> + unsigned int flags, int *ret)
> +{
> + drm_modeset_acquire_init(ctx, flags);
> +
> + if (state)
> + state->acquire_ctx = ctx;
> +
> + *ret = -EDEADLK;
> +}
> +EXPORT_SYMBOL(_drm_modeset_lock_begin);
> +
> +bool _drm_modeset_lock_loop(int *ret)
> +{
> + if (*ret == -EDEADLK) {
> + *ret = 0;
> + return true;
> + }
> +
> + return false;
> +}
> +EXPORT_SYMBOL(_drm_modeset_lock_loop);
> +
> +void _drm_modeset_lock_end(struct drm_modeset_acquire_ctx *ctx,
> + struct drm_atomic_state *state,
> + int *ret)
> +{
> + if (*ret == -EDEADLK) {
> + if (state)
> + drm_atomic_state_clear(state);
> +
> + *ret = drm_modeset_backoff(ctx);
> + if (*ret == 0) {
> + *ret = -EDEADLK;
> + return;
> + }
> + }
> +
> + drm_modeset_drop_locks(ctx);
> + drm_modeset_acquire_fini(ctx);
> +}
> +EXPORT_SYMBOL(_drm_modeset_lock_end);
> diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h
> index aafd07388eb7..5eaad2533de5 100644
> --- a/include/drm/drm_modeset_lock.h
> +++ b/include/drm/drm_modeset_lock.h
> @@ -26,6 +26,7 @@
>
> #include <linux/ww_mutex.h>
>
> +struct drm_atomic_state;
> struct drm_modeset_lock;
>
> /**
> @@ -203,4 +204,23 @@ modeset_lock_fail: \
> if (!drm_drv_uses_atomic_modeset(dev)) \
> mutex_unlock(&dev->mode_config.mutex);
>
> +void _drm_modeset_lock_begin(struct drm_modeset_acquire_ctx *ctx,
> + struct drm_atomic_state *state,
> + unsigned int flags,
> + int *ret);
> +bool _drm_modeset_lock_loop(int *ret);
> +void _drm_modeset_lock_end(struct drm_modeset_acquire_ctx *ctx,
> + struct drm_atomic_state *state,
> + int *ret);
> +
> +/*
> + * Note that one must always use "continue" rather than
> + * "break" or "return" to handle errors within the
> + * drm_modeset_lock_ctx_retry() block.
I'm not sold on loop macros with these kind of restrictions, C just isn't
a great language for these. That's why e.g. drm_connector_iter doesn't
give you a macro, but only the begin/next/end function calls explicitly.
Yes the macro we have is also not nice, but at least it's a screaming
macro since it's all uppercase, so options are all a bit sucky. Which
leads me to think we have a bit a https://xkcd.com/927/ situation going
on.
I think minimally we should have one way to do this.
-Daniel
> + */
> +#define drm_modeset_lock_ctx_retry(ctx, state, flags, ret) \
> + for (_drm_modeset_lock_begin((ctx), (state), (flags), &(ret)); \
> + _drm_modeset_lock_loop(&(ret)); \
> + _drm_modeset_lock_end((ctx), (state), &(ret)))
> +
> #endif /* DRM_MODESET_LOCK_H_ */
> --
> 2.31.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
