Re: [PATCH 1/7] drm/i915: Disable preemption and sleeping while using the punit sideband

[Hans de Goede <hdegoede@xxxxxxxxxx>]

Hi,

On 10-01-18 13:55, Chris Wilson wrote:
> 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.
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=109051
> 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@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> Cc: Hans de Goede <hdegoede@xxxxxxxxxx>

Interesting, I've added similar pm_qos code in
drivers/i2c/busses/i2c-designware-baytrail.c quite a while ago because
the CPU transitioning to higher C-state while accessing the i2c bus to
the pmic (if it is shared) also causes the SoC to hang.

I could reproduce this quite easily by doing "i2cdump" on the pmic,
usually the system would hang in one or 2 i2cdump calls.

Note IIRC this was on CHT.

I see that you also block any pmic-i2c bus accesses while doing
punit access by calling iosf_mbi_punit_acquire();

Maybe we need to move the pm_qos stuff out of
drivers/i2c/busses/i2c-designware-baytrail.c

And into iosf_mbi_punit_acquire? The i2c-designware-baytrail.c
does its own pm_qos dance directly after calling
iosf_mbi_punit_acquire / before calling iosf_mbi_punit_release();

Note the i2c-designware-baytrail.c version lacks the ping, but it
should, probably have it too.

Regards,

Hans



> ---
>   drivers/gpu/drm/i915/i915_drv.c       |  6 ++++
>   drivers/gpu/drm/i915/i915_drv.h       |  1 +
>   drivers/gpu/drm/i915/intel_sideband.c | 61 ++++++++++++++++++++++++-----------
>   3 files changed, 50 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 6c8da9d20c33..d4b90cc0130b 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -902,6 +902,9 @@ 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);
> @@ -953,6 +956,9 @@ 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 a689396d0ff6..ff3f9effc0bb 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1887,6 +1887,7 @@ 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..02bdd2e2cef6 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 +41,20 @@
>   /* 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 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;
>   
> -	WARN_ON(!mutex_is_locked(&dev_priv->sb_lock));
> +	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 +63,43 @@ 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);
> +	iosf_mbi_punit_acquire();
>   
> -	if (intel_wait_for_register(dev_priv,
> -				    VLV_IOSF_DOORBELL_REQ, IOSF_SB_BUSY, 0,
> -				    5)) {
> +	/*
> +	 * Prevent the cpu from sleeping while we use this sideband, otherwise
> +	 * the punit may cause a machine hang.
> +	 */
> +	pm_qos_update_request(&dev_priv->sb_qos, 0);
> +	on_each_cpu(ping, NULL, 1);
> +	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();
> +	pm_qos_update_request(&dev_priv->sb_qos, PM_QOS_DEFAULT_VALUE);
> +	iosf_mbi_punit_release();
>   
> -	return 0;
> +	return err;
>   }
>   
>   u32 vlv_punit_read(struct drm_i915_private *dev_priv, u32 addr)
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