[PATCH] drm/xe/oa: Set stream->pollin in xe_oa_buffer_check_unlocked

[Cavitt, Jonathan]

-----Original Message-----
From: Intel-xe <intel-xe-bounces at lists.freedesktop.org> On Behalf Of Ashutosh Dixit
Sent: Wednesday, January 15, 2025 2:20 PM
To: intel-xe at lists.freedesktop.org
Cc: Nerlige Ramappa, Umesh <umesh.nerlige.ramappa at intel.com>
Subject: [PATCH] drm/xe/oa: Set stream->pollin in xe_oa_buffer_check_unlocked
> 
> We rely on stream->pollin to decide whether or not to block during
> poll/read calls. However, currently there are blocking read code paths
> which don't even set stream->pollin. The best place to consistently set
> stream->pollin for all code paths is therefore to set it in
> xe_oa_buffer_check_unlocked.
> 
> Fixes: e936f885f1e9 ("drm/xe/oa/uapi: Expose OA stream fd")
> Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>

Minor concern below, but I don't think it's a problem, so I won't block on it.
Reviewed-by: Jonathan Cavitt <jonathan.cavitt at intel.com>

> ---
>  drivers/gpu/drm/xe/xe_oa.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_oa.c b/drivers/gpu/drm/xe/xe_oa.c
> index eeb96b5f49e2a..e27c1752aa57c 100644
> --- a/drivers/gpu/drm/xe/xe_oa.c
> +++ b/drivers/gpu/drm/xe/xe_oa.c
> @@ -237,7 +237,6 @@ static bool xe_oa_buffer_check_unlocked(struct xe_oa_stream *stream)
>  	u32 tail, hw_tail, partial_report_size, available;
>  	int report_size = stream->oa_buffer.format->size;
>  	unsigned long flags;
> -	bool pollin;
>  
>  	spin_lock_irqsave(&stream->oa_buffer.ptr_lock, flags);
>  
> @@ -282,11 +281,11 @@ static bool xe_oa_buffer_check_unlocked(struct xe_oa_stream *stream)
>  	stream->oa_buffer.tail = tail;
>  
>  	available = xe_oa_circ_diff(stream, stream->oa_buffer.tail, stream->oa_buffer.head);
> -	pollin = available >= stream->wait_num_reports * report_size;
> +	stream->pollin = available >= stream->wait_num_reports * report_size;

It looks like we call xe_oa_buffer_check_unlocked in two places.

The first is below, where we call it during xe_oa_poll_check_timer_cb.  I see we're
operating on the stream->pollin value here because we're migrating the
"stream->polling = true" code from xe_oa_poll_check_timer_cb into the
xe_oa_buffer_check_unlocked function.

However, the second location is during xe_oa_wait_unlocked.  There, we perform
xe_oa_buffer_check_unlocked in a wait_event_interruptible loop.  Is it safe to be
modifying the stream->pollin value in that case?

I'm sure it's fine, but it's something to consider.
-Jonathan Cavitt

>  
>  	spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags);
>  
> -	return pollin;
> +	return stream->pollin;
>  }
>  
>  static enum hrtimer_restart xe_oa_poll_check_timer_cb(struct hrtimer *hrtimer)
> @@ -294,10 +293,8 @@ static enum hrtimer_restart xe_oa_poll_check_timer_cb(struct hrtimer *hrtimer)
>  	struct xe_oa_stream *stream =
>  		container_of(hrtimer, typeof(*stream), poll_check_timer);
>  
> -	if (xe_oa_buffer_check_unlocked(stream)) {
> -		stream->pollin = true;
> +	if (xe_oa_buffer_check_unlocked(stream))
>  		wake_up(&stream->poll_wq);
> -	}
>  
>  	hrtimer_forward_now(hrtimer, ns_to_ktime(stream->poll_period_ns));
>  
> -- 
> 2.47.1
> 
>