[PATCH] drm/i915: Don't WARN() when sprite watermark > 0 for disabled LP2/LP3 levels

[Matt Roper <matthew.d.roper@intel.com>]

As of commit d81f04c5ef ("drm/i915: Allow preservation of watermarks, v2.")
it's now possible to have non-zero values for watermark levels that are
disabled (e.g., in the higher LP levels that can only be used when the sprite
is disabled).  Stop WARN()'ing when we see these non-zero sprite values in LP2
or LP3.

Fixes the SNB warning:

   WARNING: CPU: 1 PID: 25405 at /home/mattrope/work/kernel/gms/drivers/gpu/drm/i915/intel_pm.c:2580 ilk_program_watermarks+0x7b2/0x9d0 [i915]()
   WARN_ON(wm_lp != 1)
   Modules linked in: i915 drm_kms_helper drm bluetooth fuse iTCO_wdt iTCO_vendor_support syscopyarea sysfillrect sysimgblt fb_sys_fops tpm_tis mei_me e1000e snd_hda_codec_hdmi pcspkr tpm mei i2c_i801 lpc_ich snd_hda_codec snd_hda_core [last unloaded: drm]
   CPU: 1 PID: 25405 Comm: kms_universal_p Tainted: G     U  W       4.5.0-rc6apollolake+ #462
   Hardware name:                  /DH67GD, BIOS BLH6710H.86A.0160.2012.1204.1156 12/04/2012
    0000000000000000 ffff88009d42b918 ffffffff8143cfab ffff88009d42b960
    ffffffffa0363580 ffff88009d42b950 ffffffff81082746 ffff8800b9a24928
    ffff88009d42ba00 ffff88009d4a0000 0000000000000000 ffff88009d42ba6c
   Call Trace:
    [<ffffffff8143cfab>] dump_stack+0x4d/0x72
    [<ffffffff81082746>] warn_slowpath_common+0x86/0xc0
    [<ffffffff810827cc>] warn_slowpath_fmt+0x4c/0x50
    [<ffffffffa0292862>] ilk_program_watermarks+0x7b2/0x9d0 [i915]
    [<ffffffffa0292cb7>] ilk_initial_watermarks+0x107/0x120 [i915]
    [<ffffffffa02feffa>] intel_pre_plane_update+0x12a/0x190 [i915]
    [<ffffffffa02ffb36>] intel_atomic_commit+0x546/0xd50 [i915]
    [<ffffffffa012c9e7>] drm_atomic_commit+0x37/0x60 [drm]
    [<ffffffffa0217361>] drm_atomic_helper_disable_plane+0xb1/0xf0 [drm_kms_helper]
    [<ffffffffa011cdb4>] __setplane_internal+0x184/0x280 [drm]
    [<ffffffffa012b57a>] ? drm_modeset_lock_all_ctx+0x9a/0xb0 [drm]
    [<ffffffffa012010f>] drm_mode_setplane+0x13f/0x1c0 [drm]
    [<ffffffffa0111b52>] drm_ioctl+0x142/0x590 [drm]
    [<ffffffffa011ffd0>] ? drm_plane_check_pixel_format+0x50/0x50 [drm]
    [<ffffffff811f2744>] ? mntput+0x24/0x40
    [<ffffffff811d28d4>] ? __fput+0x194/0x200
    [<ffffffffa012dec3>] drm_compat_ioctl+0x33/0x40 [drm]
    [<ffffffffa029e1c2>] i915_compat_ioctl+0x32/0x40 [i915]
    [<ffffffff81228d72>] compat_SyS_ioctl+0xc2/0x330
    [<ffffffff810021d5>] ? exit_to_usermode_loop+0x95/0xb0
    [<ffffffff81002d2e>] do_fast_syscall_32+0x9e/0x210
    [<ffffffff8197faf2>] entry_SYSENTER_compat+0x52/0x70

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Testcase: kms_universal_plane
Fixes: d81f04c5ef ("drm/i915: Allow preservation of watermarks, v2.")
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
---
The comment above this block of code indicates that we need to turn on
WM1S_LP_EN, even if the LP level is disabled, to avoid underruns.  It's not
clear to me from the bspec why this is, so I'm trusting that the comment
is still accurate, even though we wind up with non-zero values more often
now than we previously did.

 drivers/gpu/drm/i915/intel_pm.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 823437f..9698360 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2576,10 +2576,9 @@ static void ilk_compute_wm_results(struct drm_device *dev,
 		 * Always set WM1S_LP_EN when spr_val != 0, even if the
 		 * level is disabled. Doing otherwise could cause underruns.
 		 */
-		if (INTEL_INFO(dev)->gen <= 6 && r->spr_val) {
-			WARN_ON(wm_lp != 1);
+		if (INTEL_INFO(dev)->gen <= 6 && r->spr_val)
 			results->wm_lp_spr[wm_lp - 1] = WM1S_LP_EN | r->spr_val;
-		} else
+		else
 			results->wm_lp_spr[wm_lp - 1] = r->spr_val;
 	}
 
-- 
2.1.4

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