Re: [PATCH 05/36] drm/i915: Disable preemption and sleeping while using the punit sideband

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> While we talk to the punit over its sideband, we need to prevent the cpu
> from sleeping in order to prevent a potential machine hang.
>
> Note that by itself, it appears that pm_qos_update_request (via
> intel_idle) doesn't provide a sufficient barrier to ensure that all core
> are indeed awake (out of Cstate) and that the package is awake. To do so,
> we need to supplement the pm_qos with a manual ping on_each_cpu.
>
> v2: Restrict the heavy-weight wakeup to just the ISOF_PORT_PUNIT, there
> is insufficient evidence to implicate a wider problem atm. Similarly,
> restrict the w/a to Valleyview, as Cherryview doesn't have an angry cadre
> of users.
>
> The working theory, courtesy of Ville and Hans, is the issue lies within
> the power delivery and so is likely to be unit and board specific and
> occurs when both the unit/fw require extra power at the same time as the
> cpu package is changing its own power state.
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=109051

This needs to be changed to References: as this doesn't fix that
bug.

What we could try is to ping all cpus to C1 (or c0). Then
do the op always on particular cpu (cpu0) while others are in
c0 (even forcibly spinning).

Spin a little while on whole package to max out power and
hopefully wait enough for the peak to plateau. And only afer then
proceed with the punit op. More voodoo on top of voodoo.

-Mika

> References: https://bugs.freedesktop.org/show_bug.cgi?id=102657
> References: https://bugzilla.kernel.org/show_bug.cgi?id=195255
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.c       |  6 +++
>  drivers/gpu/drm/i915/i915_drv.h       |  1 +
>  drivers/gpu/drm/i915/intel_sideband.c | 89 +++++++++++++++++++++++++++--------
>  3 files changed, 77 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 0126b222ab7f..3d0b7353fb09 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -914,6 +914,9 @@ static int i915_driver_init_early(struct drm_i915_private *dev_priv,
>  	spin_lock_init(&dev_priv->uncore.lock);
>  
>  	mutex_init(&dev_priv->sb_lock);
> +	pm_qos_add_request(&dev_priv->sb_qos,
> +			   PM_QOS_CPU_DMA_LATENCY, PM_QOS_DEFAULT_VALUE);
> +
>  	mutex_init(&dev_priv->modeset_restore_lock);
>  	mutex_init(&dev_priv->av_mutex);
>  	mutex_init(&dev_priv->wm.wm_mutex);
> @@ -965,6 +968,9 @@ static void i915_driver_cleanup_early(struct drm_i915_private *dev_priv)
>  	intel_irq_fini(dev_priv);
>  	i915_workqueues_cleanup(dev_priv);
>  	i915_engines_cleanup(dev_priv);
> +
> +	pm_qos_remove_request(&dev_priv->sb_qos);
> +	mutex_destroy(&dev_priv->sb_lock);
>  }
>  
>  static int i915_mmio_setup(struct drm_i915_private *dev_priv)
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 74b0e9d8ff62..7be61e726a79 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1636,6 +1636,7 @@ struct drm_i915_private {
>  
>  	/* Sideband mailbox protection */
>  	struct mutex sb_lock;
> +	struct pm_qos_request sb_qos;
>  
>  	/** Cached value of IMR to avoid reads in updating the bitfield */
>  	union {
> diff --git a/drivers/gpu/drm/i915/intel_sideband.c b/drivers/gpu/drm/i915/intel_sideband.c
> index 75c872bb8cc9..d56eda33734e 100644
> --- a/drivers/gpu/drm/i915/intel_sideband.c
> +++ b/drivers/gpu/drm/i915/intel_sideband.c
> @@ -22,6 +22,8 @@
>   *
>   */
>  
> +#include <asm/iosf_mbi.h>
> +
>  #include "i915_drv.h"
>  #include "intel_drv.h"
>  
> @@ -39,18 +41,48 @@
>  /* Private register write, double-word addressing, non-posted */
>  #define SB_CRWRDA_NP	0x07
>  
> -static int vlv_sideband_rw(struct drm_i915_private *dev_priv, u32 devfn,
> -			   u32 port, u32 opcode, u32 addr, u32 *val)
> +static void ping(void *info)
>  {
> -	u32 cmd, be = 0xf, bar = 0;
> -	bool is_read = (opcode == SB_MRD_NP || opcode == SB_CRRDDA_NP);
> +}
>  
> -	cmd = (devfn << IOSF_DEVFN_SHIFT) | (opcode << IOSF_OPCODE_SHIFT) |
> -		(port << IOSF_PORT_SHIFT) | (be << IOSF_BYTE_ENABLES_SHIFT) |
> -		(bar << IOSF_BAR_SHIFT);
> +static void __vlv_punit_get(struct drm_i915_private *dev_priv)
> +{
> +	iosf_mbi_punit_acquire();
>  
> -	WARN_ON(!mutex_is_locked(&dev_priv->sb_lock));
> +	/*
> +	 * Prevent the cpu from sleeping while we use this sideband, otherwise
> +	 * the punit may cause a machine hang. The issue appears to be isolated
> +	 * with changing the power state of the CPU package while changing
> +	 * the power state via the punit, and we have only observed it
> +	 * reliably on 4-core Baytail systems suggesting the issue is in the
> +	 * power delivery mechanism and likely to be be board/function
> +	 * specific. Hence we presume the workaround needs only be applied
> +	 * to the Valleyview P-unit and not all sideband communications.
> +	 */
> +	if (IS_VALLEYVIEW(dev_priv)) {
> +		pm_qos_update_request(&dev_priv->sb_qos, 0);
> +		on_each_cpu(ping, NULL, 1);
> +	}
> +}
> +
> +static void __vlv_punit_put(struct drm_i915_private *dev_priv)
> +{
> +	if (IS_VALLEYVIEW(dev_priv))
> +		pm_qos_update_request(&dev_priv->sb_qos, PM_QOS_DEFAULT_VALUE);
>  
> +	iosf_mbi_punit_release();
> +}
> +
> +static int vlv_sideband_rw(struct drm_i915_private *dev_priv,
> +			   u32 devfn, u32 port, u32 opcode,
> +			   u32 addr, u32 *val)
> +{
> +	const bool is_read = (opcode == SB_MRD_NP || opcode == SB_CRRDDA_NP);
> +	int err;
> +
> +	lockdep_assert_held(&dev_priv->sb_lock);
> +
> +	/* Flush the previous comms, just in case it failed last time. */
>  	if (intel_wait_for_register(dev_priv,
>  				    VLV_IOSF_DOORBELL_REQ, IOSF_SB_BUSY, 0,
>  				    5)) {
> @@ -59,22 +91,33 @@ static int vlv_sideband_rw(struct drm_i915_private *dev_priv, u32 devfn,
>  		return -EAGAIN;
>  	}
>  
> -	I915_WRITE(VLV_IOSF_ADDR, addr);
> -	I915_WRITE(VLV_IOSF_DATA, is_read ? 0 : *val);
> -	I915_WRITE(VLV_IOSF_DOORBELL_REQ, cmd);
> -
> -	if (intel_wait_for_register(dev_priv,
> -				    VLV_IOSF_DOORBELL_REQ, IOSF_SB_BUSY, 0,
> -				    5)) {
> +	preempt_disable();
> +
> +	I915_WRITE_FW(VLV_IOSF_ADDR, addr);
> +	I915_WRITE_FW(VLV_IOSF_DATA, is_read ? 0 : *val);
> +	I915_WRITE_FW(VLV_IOSF_DOORBELL_REQ,
> +		      (devfn << IOSF_DEVFN_SHIFT) |
> +		      (opcode << IOSF_OPCODE_SHIFT) |
> +		      (port << IOSF_PORT_SHIFT) |
> +		      (0xf << IOSF_BYTE_ENABLES_SHIFT) |
> +		      (0 << IOSF_BAR_SHIFT) |
> +		      IOSF_SB_BUSY);
> +
> +	if (__intel_wait_for_register_fw(dev_priv,
> +					 VLV_IOSF_DOORBELL_REQ, IOSF_SB_BUSY, 0,
> +					 10000, 0, NULL) == 0) {
> +		if (is_read)
> +			*val = I915_READ_FW(VLV_IOSF_DATA);
> +		err = 0;
> +	} else {
>  		DRM_DEBUG_DRIVER("IOSF sideband finish wait (%s) timed out\n",
>  				 is_read ? "read" : "write");
> -		return -ETIMEDOUT;
> +		err = -ETIMEDOUT;
>  	}
>  
> -	if (is_read)
> -		*val = I915_READ(VLV_IOSF_DATA);
> +	preempt_enable();
>  
> -	return 0;
> +	return err;
>  }
>  
>  u32 vlv_punit_read(struct drm_i915_private *dev_priv, u32 addr)
> @@ -84,8 +127,12 @@ u32 vlv_punit_read(struct drm_i915_private *dev_priv, u32 addr)
>  	WARN_ON(!mutex_is_locked(&dev_priv->pcu_lock));
>  
>  	mutex_lock(&dev_priv->sb_lock);
> +	__vlv_punit_get(dev_priv);
> +
>  	vlv_sideband_rw(dev_priv, PCI_DEVFN(0, 0), IOSF_PORT_PUNIT,
>  			SB_CRRDDA_NP, addr, &val);
> +
> +	__vlv_punit_put(dev_priv);
>  	mutex_unlock(&dev_priv->sb_lock);
>  
>  	return val;
> @@ -98,8 +145,12 @@ int vlv_punit_write(struct drm_i915_private *dev_priv, u32 addr, u32 val)
>  	WARN_ON(!mutex_is_locked(&dev_priv->pcu_lock));
>  
>  	mutex_lock(&dev_priv->sb_lock);
> +	__vlv_punit_get(dev_priv);
> +
>  	err = vlv_sideband_rw(dev_priv, PCI_DEVFN(0, 0), IOSF_PORT_PUNIT,
>  			      SB_CRWRDA_NP, addr, &val);
> +
> +	__vlv_punit_put(dev_priv);
>  	mutex_unlock(&dev_priv->sb_lock);
>  
>  	return err;
> -- 
> 2.16.2
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx