linux-kernel - Re: [Y2038] [PATCH] drm/sti: Use 64-bit timestamps

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Message-ID: <7376001.70fALvhWdv@wuerfel>
Date:	Sun, 17 Apr 2016 01:39:33 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	y2038@...ts.linaro.org
Cc:	Tina Ruchandani <ruchandani.tina@...il.com>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	David Airlie <airlied@...ux.ie>,
	Benjamin Gaignard <benjamin.gaignard@...aro.org>,
	Vincent Abriou <vincent.abriou@...com>
Subject: Re: [Y2038] [PATCH] drm/sti: Use 64-bit timestamps

On Wednesday 13 April 2016 02:28:02 Tina Ruchandani wrote:
> 'struct timespec' uses a 32-bit field for seconds, which
> will overflow in year 2038 and beyond. This patch is part
> of a larger attempt to remove instances of timeval, timespec
> and time_t, all of which suffer from the y2038 issue, from the
> kernel.
> 
> Signed-off-by: Tina Ruchandani <ruchandani.tina@...il.com>

Looks good in principle. Two small points:

>  void sti_plane_update_fps(struct sti_plane *plane,
>  			  bool new_frame,
>  			  bool new_field)
>  {
> -	struct timespec now;
> +	ktime_t now;
>  	struct sti_fps_info *fps;
>  	int fpks, fipks, ms_since_last, num_frames, num_fields;
> 
> -	getrawmonotonic(&now);
> +	now = ktime_get();

It's unclear why the driver was using getrawmonotonic() here rather
than ktime_get_ts(). The code is fairly new, so Vincent can
probably explain this.

If it was intentional, we should use ktime_get_raw() instead of
ktime_get().

> @@ -76,7 +66,7 @@ void sti_plane_update_fps(struct sti_plane *plane,
>  		return;
> 
>  	fps->curr_frame_counter++;
> -	ms_since_last = sti_plane_timespec_ms_diff(now, fps->last_timestamp);
> +	ms_since_last = ktime_to_ms(ktime_sub(now, fps->last_timestamp));
>  	num_frames = fps->curr_frame_counter - fps->last_frame_counter;

This could be expressed in a more compact way using ktime_ms_delta().

	Arnd