/*
 * Thunderbolt Cactus Ridge driver - capabilities lookup
 *
 * Copyright (c) 2014 Andreas Noever <andreas.noever@gmail.com>
 */

#include <linux/slab.h>
#include <linux/errno.h>

#include "tb.h"


struct tb_cap_any {
	union {
		struct tb_cap_basic basic;
		struct tb_cap_extended_short extended_short;
		struct tb_cap_extended_long extended_long;
	};
} __packed;

static bool tb_cap_is_basic(struct tb_cap_any *cap)
{
	/* basic.cap is u8. This checks only the lower 8 bit of cap. */
	return cap->basic.cap != 5;
}

static bool tb_cap_is_long(struct tb_cap_any *cap)
{
	return !tb_cap_is_basic(cap)
	       && cap->extended_short.next == 0
	       && cap->extended_short.length == 0;
}

static enum tb_cap tb_cap(struct tb_cap_any *cap)
{
	if (tb_cap_is_basic(cap))
		return cap->basic.cap;
	else
		/* extended_short/long have cap at the same offset. */
		return cap->extended_short.cap;
}

static u32 tb_cap_next(struct tb_cap_any *cap, u32 offset)
{
	int next;
	if (offset == 1) {
		/*
		 * The first pointer is part of the switch header and always
		 * a simple pointer.
		 */
		next = cap->basic.next;
	} else {
		/*
		 * Somehow Intel decided to use 3 different types of capability
		 * headers. It is not like anyone could have predicted that
		 * single byte offsets are not enough...
		 */
		if (tb_cap_is_basic(cap))
			next = cap->basic.next;
		else if (!tb_cap_is_long(cap))
			next = cap->extended_short.next;
		else
			next = cap->extended_long.next;
	}
	/*
	 * "Hey, we could terminate some capability lists with a null offset
	 *  and others with a pointer to the last element." - "Great idea!"
	 */
	if (next == offset)
		return 0;
	return next;
}

/**
 * tb_find_cap() - find a capability
 *
 * Return: Returns a positive offset if the capability was found and 0 if not.
 * Returns an error code on failure.
 */
int tb_find_cap(struct tb_port *port, enum tb_cfg_space space, enum tb_cap cap)
{
	u32 offset = 1;
	struct tb_cap_any header;
	int res;
	int retries = 10;
	while (retries--) {
		res = tb_port_read(port, &header, space, offset, 1);
		if (res) {
			/* Intel needs some help with linked lists. */
			if (space == TB_CFG_PORT && offset == 0xa
			    && port->config.type == TB_TYPE_DP_HDMI_OUT) {
				offset = 0x39;
				continue;
			}
			return res;
		}
		if (offset != 1) {
			if (tb_cap(&header) == cap)
				return offset;
			if (tb_cap_is_long(&header)) {
				/* tb_cap_extended_long is 2 dwords */
				res = tb_port_read(port, &header, space,
						   offset, 2);
				if (res)
					return res;
			}
		}
		offset = tb_cap_next(&header, offset);
		if (!offset)
			return 0;
	}
	tb_port_WARN(port,
		     "run out of retries while looking for cap %#x in config space %d, last offset: %#x\n",
		     cap, space, offset);
	return -EIO;
}
select>
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<div class='path'>path: <a href='/cgit.cgi/linux/net-next.git/commit/?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>root</a>/<a href='/cgit.cgi/linux/net-next.git/commit/tools?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>tools</a>/<a href='/cgit.cgi/linux/net-next.git/commit/tools/testing?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>testing</a>/<a href='/cgit.cgi/linux/net-next.git/commit/tools/testing/selftests?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>selftests</a>/<a href='/cgit.cgi/linux/net-next.git/commit/tools/testing/selftests/rcutorture?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>rcutorture</a>/<a href='/cgit.cgi/linux/net-next.git/commit/tools/testing/selftests/rcutorture/configs?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>configs</a>/<a href='/cgit.cgi/linux/net-next.git/commit/tools/testing/selftests/rcutorture/configs/rcuperf?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>rcuperf</a>/<a href='/cgit.cgi/linux/net-next.git/commit/tools/testing/selftests/rcutorture/configs/rcuperf/TREE?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>TREE</a></div><div class='content'><div class='cgit-panel'><b>diff options</b><form method='get'><input type='hidden' name='id' value='39cb2c9a316e77f6dfba96c543e55b6672d5a37e'/><table><tr><td colspan='2'/></tr><tr><td class='label'>context:</td><td class='ctrl'><select name='context' onchange='this.form.submit();'><option value='1'>1</option><option value='2'>2</option><option value='3' selected='selected'>3</option><option value='4'>4</option><option value='5'>5</option><option value='6'>6</option><option value='7'>7</option><option value='8'>8</option><option value='9'>9</option><option value='10'>10</option><option value='15'>15</option><option value='20'>20</option><option value='25'>25</option><option value='30'>30</option><option value='35'>35</option><option value='40'>40</option></select></td></tr><tr><td class='label'>space:</td><td class='ctrl'><select name='ignorews' onchange='this.form.submit();'><option value='0' selected='selected'>include</option><option value='1'>ignore</option></select></td></tr><tr><td class='label'>mode:</td><td class='ctrl'><select name='dt' onchange='this.form.submit();'><option value='0' selected='selected'>unified</option><option value='1'>ssdiff</option><option value='2'>stat only</option></select></td></tr><tr><td/><td class='ctrl'><noscript><input type='submit' value='reload'/></noscript></td></tr></table></form></div><table summary='commit info' class='commit-info'>
<tr><th>author</th><td>Linus Torvalds &lt;torvalds@linux-foundation.org&gt;</td><td class='right'>2017-01-29 13:50:06 -0800</td></tr>
<tr><th>committer</th><td>Linus Torvalds &lt;torvalds@linux-foundation.org&gt;</td><td class='right'>2017-01-29 13:50:06 -0800</td></tr>
<tr><th>commit</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/tools/testing/selftests/rcutorture/configs/rcuperf/TREE?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>39cb2c9a316e77f6dfba96c543e55b6672d5a37e</a> (<a href='/cgit.cgi/linux/net-next.git/patch/tools/testing/selftests/rcutorture/configs/rcuperf/TREE?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>patch</a>)</td></tr>
<tr><th>tree</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/tree/?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>98fe974ee4e20121253de7f61fc8d01bdb3821c1</a> /<a href='/cgit.cgi/linux/net-next.git/tree/tools/testing/selftests/rcutorture/configs/rcuperf/TREE?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>tools/testing/selftests/rcutorture/configs/rcuperf/TREE</a></td></tr>
<tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/tools/testing/selftests/rcutorture/configs/rcuperf/TREE?id=2c5d9555d6d937966d79d4c6529a5f7b9206e405'>2c5d9555d6d937966d79d4c6529a5f7b9206e405</a> (<a href='/cgit.cgi/linux/net-next.git/diff/tools/testing/selftests/rcutorture/configs/rcuperf/TREE?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e&amp;id2=2c5d9555d6d937966d79d4c6529a5f7b9206e405'>diff</a>)</td></tr></table>
<div class='commit-subject'>drm/i915: Check for NULL i915_vma in intel_unpin_fb_obj()</div><div class='commit-msg'>I've seen this trigger twice now, where the i915_gem_object_to_ggtt()
call in intel_unpin_fb_obj() returns NULL, resulting in an oops
immediately afterwards as the (inlined) call to i915_vma_unpin_fence()
tries to dereference it.

It seems to be some race condition where the object is going away at
shutdown time, since both times happened when shutting down the X
server.  The call chains were different:

 - VT ioctl(KDSETMODE, KD_TEXT):

    intel_cleanup_plane_fb+0x5b/0xa0 [i915]
    drm_atomic_helper_cleanup_planes+0x6f/0x90 [drm_kms_helper]
    intel_atomic_commit_tail+0x749/0xfe0 [i915]
    intel_atomic_commit+0x3cb/0x4f0 [i915]
    drm_atomic_commit+0x4b/0x50 [drm]
    restore_fbdev_mode+0x14c/0x2a0 [drm_kms_helper]
    drm_fb_helper_restore_fbdev_mode_unlocked+0x34/0x80 [drm_kms_helper]
    drm_fb_helper_set_par+0x2d/0x60 [drm_kms_helper]
    intel_fbdev_set_par+0x18/0x70 [i915]
    fb_set_var+0x236/0x460
    fbcon_blank+0x30f/0x350
    do_unblank_screen+0xd2/0x1a0
    vt_ioctl+0x507/0x12a0
    tty_ioctl+0x355/0xc30
    do_vfs_ioctl+0xa3/0x5e0
    SyS_ioctl+0x79/0x90
    entry_SYSCALL_64_fastpath+0x13/0x94

 - i915 unpin_work workqueue:

    intel_unpin_work_fn+0x58/0x140 [i915]
    process_one_work+0x1f1/0x480
    worker_thread+0x48/0x4d0
    kthread+0x101/0x140

and this patch purely papers over the issue by adding a NULL pointer
check and a WARN_ON_ONCE() to avoid the oops that would then generally
make the machine unresponsive.

Other callers of i915_gem_object_to_ggtt() seem to also check for the
returned pointer being NULL and warn about it, so this clearly has
happened before in other places.

[ Reported it originally to the i915 developers on Jan 8, applying the
  ugly workaround on my own now after triggering the problem for the
  second time with no feedback.

  This is likely to be the same bug reported as

     https://bugs.freedesktop.org/show_bug.cgi?id=98829
     https://bugs.freedesktop.org/show_bug.cgi?id=99134

  which has a patch for the underlying problem, but it hasn't gotten to
  me, so I'm applying the workaround. ]

Cc: Daniel Vetter &lt;daniel.vetter@intel.com&gt;
Cc: Jani Nikula &lt;jani.nikula@linux.intel.com&gt;
Cc: Ville Syrjälä &lt;ville.syrjala@linux.intel.com&gt;
Cc: Chris Wilson &lt;chris@chris-wilson.co.uk&gt;
Cc: Maarten Lankhorst &lt;maarten.lankhorst@linux.intel.com&gt;
Cc: Tvrtko Ursulin &lt;tvrtko.ursulin@intel.com&gt;
Cc: Imre Deak &lt;imre.deak@intel.com&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</div><div class='diffstat-header'><a href='/cgit.cgi/linux/net-next.git/diff/?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>Diffstat</a> (limited to 'tools/testing/selftests/rcutorture/configs/rcuperf/TREE')</div><table summary='diffstat' class='diffstat'>