On Tue, Jan 30, 2018 at 01:47:10PM +0200, Imre Deak wrote:
> Currently we see sporadic timeouts during CDCLK changing both on BXT and
> GLK as reported by the Bugzilla: ticket. It's easy to reproduce this by
> changing the frequency in a tight loop after blanking the display. The
> upper bound for the completion time is 800us based on my tests, so
> increase it from the current 500us to 2ms; with that I couldn't trigger
> the problem either on BXT or GLK.
>
> Note that timeouts happened during both the change notification and the
> voltage level setting PCODE request. (For the latter one BSpec doesn't
> require us to wait for completion before further HW programming.)
>
> This issue is similar to
> 2c7d0602c815 ("drm/i915/gen9: Fix PCODE polling during CDCLK change
> notification")
> but there the PCODE request does complete (as shown by the mbox
> busy flag), only the reply we get from PCODE indicates a failure.
> So there we keep resending the request until a success reply, here we
> just have to increase the timeout for the one PCODE request we send.
>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v4.4+
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103326
> Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 6 +++++-
> drivers/gpu/drm/i915/intel_cdclk.c | 20 +++++++++++++++-----
> drivers/gpu/drm/i915/intel_pm.c | 6 +++---
> 3 files changed, 23 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 454d8f937fae..5e293be4e51d 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3723,7 +3723,11 @@ extern void intel_display_print_error_state(struct drm_i915_error_state_buf *e,
> struct intel_display_error_state *error);
>
> int sandybridge_pcode_read(struct drm_i915_private *dev_priv, u32 mbox, u32 *val);
> -int sandybridge_pcode_write(struct drm_i915_private *dev_priv, u32 mbox, u32 val);
> +int snb_pcode_request(struct drm_i915_private *dev_priv, u32 mbox, u32 val,
> + int timeout_us);
> +#define sandybridge_pcode_write(dev_priv, mbox, val) \
> + snb_pcode_request(dev_priv, mbox, val, 500)
The naming feels a bit inconsistent. snb_pcode_request() is nothing
like skl_pcode_request(), rather it's just an improved
sandybridge_pcode_write().
> +
> int skl_pcode_request(struct drm_i915_private *dev_priv, u32 mbox, u32 request,
> u32 reply_mask, u32 reply, int timeout_base_ms);
>
> diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c
> index c4392ea34a3d..5057336c40ba 100644
> --- a/drivers/gpu/drm/i915/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/intel_cdclk.c
> @@ -1370,10 +1370,14 @@ static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
> break;
> }
>
> - /* Inform power controller of upcoming frequency change */
> + /*
> + * Inform power controller of upcoming frequency change. BSpec
> + * requires us to wait up to 150usec, but that leads to timeouts;
> + * the 2ms used here is based on experiment.
> + */
> mutex_lock(&dev_priv->pcu_lock);
> - ret = sandybridge_pcode_write(dev_priv, HSW_PCODE_DE_WRITE_FREQ_REQ,
> - 0x80000000);
> + ret = snb_pcode_request(dev_priv, HSW_PCODE_DE_WRITE_FREQ_REQ,
> + 0x80000000, 2000);
> mutex_unlock(&dev_priv->pcu_lock);
>
> if (ret) {
> @@ -1404,8 +1408,14 @@ static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
> I915_WRITE(CDCLK_CTL, val);
>
> mutex_lock(&dev_priv->pcu_lock);
> - ret = sandybridge_pcode_write(dev_priv, HSW_PCODE_DE_WRITE_FREQ_REQ,
> - cdclk_state->voltage_level);
> + /*
> + * The timeout isn't specified, the 2ms used here is based on
> + * experiment.
> + * FIXME: Waiting for the request completion could be delayed until
> + * the next PCODE request based on BSpec.
> + */
> + ret = snb_pcode_request(dev_priv, HSW_PCODE_DE_WRITE_FREQ_REQ,
> + cdclk_state->voltage_level, 2000);
> mutex_unlock(&dev_priv->pcu_lock);
>
> if (ret) {
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 0b92ea1dbd40..f6f4dbacb9af 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -9169,8 +9169,8 @@ int sandybridge_pcode_read(struct drm_i915_private *dev_priv, u32 mbox, u32 *val
> return 0;
> }
>
> -int sandybridge_pcode_write(struct drm_i915_private *dev_priv,
> - u32 mbox, u32 val)
> +int snb_pcode_request(struct drm_i915_private *dev_priv,
> + u32 mbox, u32 val, int timeout_us)
> {
> int status;
>
> @@ -9193,7 +9193,7 @@ int sandybridge_pcode_write(struct drm_i915_private *dev_priv,
>
> if (__intel_wait_for_register_fw(dev_priv,
> GEN6_PCODE_MAILBOX, GEN6_PCODE_READY, 0,
> - 500, 0, NULL)) {
> + timeout_us, 0, NULL)) {
> DRM_ERROR("timeout waiting for pcode write of 0x%08x to mbox %x to finish for %ps\n",
> val, mbox, __builtin_return_address(0));
> return -ETIMEDOUT;
> --
> 2.13.2
--
Ville Syrjälä
Intel OTC