Re: [PATCH] drm/i915/dsi: Do not clear DPOUNIT_CLOCK_GATE_DISABLE from vlv_init_display_clock_gating

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Dec 01, 2016 at 04:39:57PM +0100, Hans de Goede wrote:
> On my Cherrytrail CUBE iwork8 Air tablet PIPE-A would get stuck on loading
> i915 at boot 1 out of every 3 boots, resulting in a non functional LCD.
> Once the i915 driver has successfully loaded, the panel can be disabled /
> enabled without hitting this issue.
> 
> The getting stuck is caused by vlv_init_display_clock_gating() clearing
> the DPOUNIT_CLOCK_GATE_DISABLE bit in DSPCLK_GATE_D when called from
> chv_pipe_power_well_ops.enable() on driver load, while PIPE-A is enabled
> driving the DSI LCD by the BIOS.
> 
> Clearing this bit while DSI is in use is a known issue and
> intel_dsi_pre_enable() / intel_dsi_post_disable() already set / clear it
> as appropriate.
> 
> This commit modifies vlv_init_display_clock_gating() to leave the
> DPOUNIT_CLOCK_GATE_DISABLE bit alone fixing PIPE-A getting stuck.
> 
> BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=97330
> Cc: stable@vger.kernel.org
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/gpu/drm/i915/intel_runtime_pm.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
> index 356c662..b5ce7cb 100644
> --- a/drivers/gpu/drm/i915/intel_runtime_pm.c
> +++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
> @@ -1039,7 +1039,18 @@ static bool vlv_power_well_enabled(struct drm_i915_private *dev_priv,
>  
>  static void vlv_init_display_clock_gating(struct drm_i915_private *dev_priv)
>  {
> -	I915_WRITE(DSPCLK_GATE_D, VRHUNIT_CLOCK_GATE_DISABLE);
> +	u32 val;
> +
> +	/*
> +	 * When on driver load, PIPE A may be active and driving a DSI display.
> +	 * Preserve DPOUNIT_CLOCK_GATE_DISABLE to avoid PIPE A getting stuck
> +	 * (and never recovering) in this case. intel_dsi_post_disable() will
> +	 * clear it when we turn off the display.

Why are you talking only about pipe A here?

> +	 */
> +	val = I915_READ(DSPCLK_GATE_D);
> +	val &= DPOUNIT_CLOCK_GATE_DISABLE;
> +	val |= VRHUNIT_CLOCK_GATE_DISABLE;
> +	I915_WRITE(DSPCLK_GATE_D, val);
>  
>  	/*
>  	 * Disable trickle feed and enable pnd deadline calculation
> -- 
> 2.9.3
> 
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-- 
Ville Syrjälä
Intel OTC
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