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    Subject[PATCH 4.19 044/110] drm/i915: Disable LP3 watermarks on all SNB machines
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Ville Syrjälä <ville.syrjala@linux.intel.com>

    commit 21556350ade3cb5d7afecc8b3544e56431d21695 upstream.

    I have a Thinkpad X220 Tablet in my hands that is losing vblank
    interrupts whenever LP3 watermarks are used.

    If I nudge the latency value written to the WM3 register just
    by one in either direction the problem disappears. That to me
    suggests that the punit will not enter the corrsponding
    powersave mode (MPLL shutdown IIRC) unless the latency value
    in the register matches exactly what we read from SSKPD. Ie.
    it's not really a latency value but rather just a cookie
    by which the punit can identify the desired power saving state.
    On HSW/BDW this was changed such that we actually just write
    the WM level number into those bits, which makes much more
    sense given the observed behaviour.

    We could try to handle this by disallowing LP3 watermarks
    only when vblank interrupts are enabled but we'd first have
    to prove that only vblank interrupts are affected, which
    seems unlikely. Also we can't grab the wm mutex from the
    vblank enable/disable hooks because those are called with
    various spinlocks held. Thus we'd have to redesigne the
    watermark locking. So to play it safe and keep the code
    simple we simply disable LP3 watermarks on all SNB machines.

    To do that we simply zero out the latency values for
    watermark level 3, and we adjust the watermark computation
    to check for that. The behaviour now matches that of the
    g4x/vlv/skl wm code in the presence of a zeroed latency
    value.

    v2: s/USHRT_MAX/U32_MAX/ for consistency with the types (Chris)

    Cc: stable@vger.kernel.org
    Cc: Chris Wilson <chris@chris-wilson.co.uk>
    Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101269
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103713
    Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20181114173440.6730-1-ville.syrjala@linux.intel.com
    (cherry picked from commit 03981c6ebec4fc7056b9b45f847393aeac90d060)
    Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/i915/intel_pm.c | 41 +++++++++++++++++++++++++++++++++++++++-
    1 file changed, 40 insertions(+), 1 deletion(-)

    --- a/drivers/gpu/drm/i915/intel_pm.c
    +++ b/drivers/gpu/drm/i915/intel_pm.c
    @@ -2492,6 +2492,9 @@ static uint32_t ilk_compute_pri_wm(const
    uint32_t method1, method2;
    int cpp;

    + if (mem_value == 0)
    + return U32_MAX;
    +
    if (!intel_wm_plane_visible(cstate, pstate))
    return 0;

    @@ -2521,6 +2524,9 @@ static uint32_t ilk_compute_spr_wm(const
    uint32_t method1, method2;
    int cpp;

    + if (mem_value == 0)
    + return U32_MAX;
    +
    if (!intel_wm_plane_visible(cstate, pstate))
    return 0;

    @@ -2544,6 +2550,9 @@ static uint32_t ilk_compute_cur_wm(const
    {
    int cpp;

    + if (mem_value == 0)
    + return U32_MAX;
    +
    if (!intel_wm_plane_visible(cstate, pstate))
    return 0;

    @@ -2998,6 +3007,34 @@ static void snb_wm_latency_quirk(struct
    intel_print_wm_latency(dev_priv, "Cursor", dev_priv->wm.cur_latency);
    }

    +static void snb_wm_lp3_irq_quirk(struct drm_i915_private *dev_priv)
    +{
    + /*
    + * On some SNB machines (Thinkpad X220 Tablet at least)
    + * LP3 usage can cause vblank interrupts to be lost.
    + * The DEIIR bit will go high but it looks like the CPU
    + * never gets interrupted.
    + *
    + * It's not clear whether other interrupt source could
    + * be affected or if this is somehow limited to vblank
    + * interrupts only. To play it safe we disable LP3
    + * watermarks entirely.
    + */
    + if (dev_priv->wm.pri_latency[3] == 0 &&
    + dev_priv->wm.spr_latency[3] == 0 &&
    + dev_priv->wm.cur_latency[3] == 0)
    + return;
    +
    + dev_priv->wm.pri_latency[3] = 0;
    + dev_priv->wm.spr_latency[3] = 0;
    + dev_priv->wm.cur_latency[3] = 0;
    +
    + DRM_DEBUG_KMS("LP3 watermarks disabled due to potential for lost interrupts\n");
    + intel_print_wm_latency(dev_priv, "Primary", dev_priv->wm.pri_latency);
    + intel_print_wm_latency(dev_priv, "Sprite", dev_priv->wm.spr_latency);
    + intel_print_wm_latency(dev_priv, "Cursor", dev_priv->wm.cur_latency);
    +}
    +
    static void ilk_setup_wm_latency(struct drm_i915_private *dev_priv)
    {
    intel_read_wm_latency(dev_priv, dev_priv->wm.pri_latency);
    @@ -3014,8 +3051,10 @@ static void ilk_setup_wm_latency(struct
    intel_print_wm_latency(dev_priv, "Sprite", dev_priv->wm.spr_latency);
    intel_print_wm_latency(dev_priv, "Cursor", dev_priv->wm.cur_latency);

    - if (IS_GEN6(dev_priv))
    + if (IS_GEN6(dev_priv)) {
    snb_wm_latency_quirk(dev_priv);
    + snb_wm_lp3_irq_quirk(dev_priv);
    + }
    }

    static void skl_setup_wm_latency(struct drm_i915_private *dev_priv)

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