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From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: David Lechner <david@lechnology.com>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH 6/6] drm/tinydrm: Support device unplug
Date: Mon, 04 Sep 2017 12:38:35 +0300	[thread overview]
Message-ID: <6462996.0y39oE8rbp@avalon> (raw)
In-Reply-To: <20170904090437.b7rc3fadqzcqct2p@phenom.ffwll.local>

Hi Daniel,

On Monday, 4 September 2017 12:04:38 EEST Daniel Vetter wrote:
> On Mon, Sep 04, 2017 at 11:41:05AM +0300, Laurent Pinchart wrote:
> > On Monday, 4 September 2017 10:26:15 EEST Daniel Vetter wrote:

[snip]

> >> Yup, expect imo this should be done in drm core (as much as possible,
> >> i.e. for ioctl at least, standard sysfs), plus then enter/exit exported
> >> to drivers for their stuff.
> >> 
> >> And it really needs to be srcu. For kms drivers the atomic_inc/dec wont
> >> matter, for render drivers it will show up (some of our ioctls are 100%
> >> lock less in the fastpath, not a single atomic op in there).
> > 
> > Don't forget that we need to check the disconnect flag when entering
> > ioctls to return -ENODEV. I'm open to clever solutions, but I'd first aim
> > for correctness with a lock and then replace the internal implementation.
> 
> As Noralf pointed out, we already check for drm_dev_is_unplugged(). Maybe
> not in all places, but that can be fixed.

Yes, but I believe that both the unplugged check and enter reference get need 
to be done atomically.

> And you can't first make all ioctl slower and then fix it up, at least not
> spread over multiple patch series. I guess for developing, doing the
> simpler atomic counter first is ok. But the same patch series needs to
> move over to srcu at the end.

To SRCU or something similar, yes.

> But I'm not sure that's a good idea, since implementing this 100% correctly
> using your atomic_t idea means you implement half of srcu anyway. Otoh
> discovering all those races should be an interesting journey :-)

-- 
Regards,

Laurent Pinchart

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  reply	other threads:[~2017-09-04  9:38 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-28 17:17 [PATCH 0/6] drm/tinydrm: Support device unplug Noralf Trønnes
2017-08-28 17:17 ` [PATCH 1/6] drm/fb-helper: Avoid NULL ptr dereference in fb_set_suspend() Noralf Trønnes
2017-08-28 21:34   ` Daniel Vetter
2017-08-31  9:30     ` Laurent Pinchart
2017-09-02 12:46       ` Noralf Trønnes
2017-08-28 17:17 ` [PATCH 2/6] drm/fb-helper: Support device unplug Noralf Trønnes
2017-08-28 21:41   ` Daniel Vetter
2017-08-29 16:17     ` Noralf Trønnes
2017-08-30  7:29       ` Daniel Vetter
2017-08-30 13:45         ` Noralf Trønnes
2017-08-28 17:17 ` [PATCH 3/6] drm/fb-cma-helper: " Noralf Trønnes
2017-08-28 21:46   ` Daniel Vetter
2017-08-29 17:23     ` Noralf Trønnes
2017-08-30  7:36       ` Daniel Vetter
2017-08-28 17:17 ` [PATCH 4/6] drm/tinydrm: Embed drm_device in tinydrm_device Noralf Trønnes
2017-08-28 21:47   ` Daniel Vetter
2017-08-29 19:09   ` David Lechner
2017-08-31 10:18   ` Laurent Pinchart
2017-08-31 17:16     ` Noralf Trønnes
2017-09-01  7:28       ` Laurent Pinchart
2017-09-01 18:46         ` Noralf Trønnes
2017-08-28 17:17 ` [PATCH 5/6] drm/tinydrm/mi0283qt: Let the display pipe handle power Noralf Trønnes
2017-08-28 17:17 ` [PATCH 6/6] drm/tinydrm: Support device unplug Noralf Trønnes
2017-08-28 21:56   ` Daniel Vetter
2017-08-30 16:31     ` Noralf Trønnes
2017-08-30 17:18       ` Daniel Vetter
2017-08-31 12:59         ` Laurent Pinchart
2017-08-31 19:22           ` Noralf Trønnes
2017-09-01  8:38             ` Laurent Pinchart
2017-09-02 20:59               ` Noralf Trønnes
2017-09-04  7:26             ` Daniel Vetter
2017-09-04  8:41               ` Laurent Pinchart
2017-09-04  9:04                 ` Daniel Vetter
2017-09-04  9:38                   ` Laurent Pinchart [this message]
2017-09-04 12:30                   ` Noralf Trønnes
2017-09-04 15:20                     ` Daniel Vetter
2017-09-04 15:54                       ` Noralf Trønnes
2017-09-04 16:39                         ` Daniel Vetter
2017-08-28 21:58 ` [PATCH 0/6] " Daniel Vetter
2017-08-29 18:05   ` Noralf Trønnes

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