[PATCH 03/13] drm/i915/dmc_wl: Check for non-zero refcount in release work

[Luca Coelho]

On Mon, 2024-10-21 at 19:27 -0300, Gustavo Sousa wrote:
> When the DMC wakelock refcount reaches zero, we know that there are no
> users and that we can do the actual release operation on the hardware,
> which is queued with a delayed work. The idea of the delayed work is to
> avoid performing the release if a new lock user appears (i.e. refcount
> gets incremented) in a very short period of time.
> 
> Based on the above, the release work should bail out if refcount is
> non-zero (meaning new lock users appeared in the meantime), but our
> current code actually does the opposite: it bails when refcount is zero.
> That means that the wakelock is not released when it should be; and
> that, when the work is not canceled in time, it ends up being releasing
> when it should not.
> 
> Fix that by inverting the condition.
> 
> Signed-off-by: Gustavo Sousa <gustavo.sousa at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dmc_wl.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dmc_wl.c b/drivers/gpu/drm/i915/display/intel_dmc_wl.c
> index 8056a3c8666c..c298aef89449 100644
> --- a/drivers/gpu/drm/i915/display/intel_dmc_wl.c
> +++ b/drivers/gpu/drm/i915/display/intel_dmc_wl.c
> @@ -72,8 +72,11 @@ static void intel_dmc_wl_work(struct work_struct *work)
>  
>  	spin_lock_irqsave(&wl->lock, flags);
>  
> -	/* Bail out if refcount reached zero while waiting for the spinlock */
> -	if (!refcount_read(&wl->refcount))
> +	/*
> +	 * Bail out if refcount became non-zero while waiting for the spinlock,
> +	 * meaning that the lock is now taken again.
> +	 */
> +	if (refcount_read(&wl->refcount))
>  		goto out_unlock;
>  
>  	__intel_de_rmw_nowl(display, DMC_WAKELOCK1_CTL, DMC_WAKELOCK_CTL_REQ, 0);

Oh, this was probably hard to catch.  I think this is a buggy leftover
from my earlier implementations where I was decreasing the refcount
only here.

Reviewed-by: Luca Coelho <luciano.coelho at intel.com>

--
Cheers,
Luca.