Re: [PATCH v2 12/13] drm/i915: Listen for PMIC bus access notifications

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

On Mon, Jan 23, 2017 at 10:09:57PM +0100, Hans de Goede wrote:
> Listen for PMIC bus access notifications and get FORCEWAKE_ALL while
> the bus is accessed to avoid needing to do any forcewakes, which need
> PMIC bus access, while the PMIC bus is busy:
> 
> This fixes errors like these showing up in dmesg, usually followed
> by a gfx or system freeze:
> 
> [drm:fw_domains_get [i915]] *ERROR* render: timed out waiting for forcewake ack request.
> [drm:fw_domains_get [i915]] *MEDIA* render: timed out waiting for forcewake ack request.
> i2c_designware 808622C1:06: punit semaphore timed out, resetting
> i2c_designware 808622C1:06: PUNIT SEM: 2
> i2c_designware 808622C1:06: couldn't acquire bus ownership
> 
> Downside of this approach is that it causes wakeups whenever the PMIC
> bus is accessed. Unfortunately we cannot simply wait for the PMIC bus
> to go idle when we hit a race, as forcewakes may be done from interrupt
> handlers where we cannot sleep to wait for the i2c PMIC bus access to
> finish.
> 
> Note that the notifications and thus the wakeups will only happen on
> baytrail / cherrytrail devices using PMICs with a shared i2c bus for
> P-Unit and host PMIC access (i2c busses with a _SEM method in their
> APCI node), e.g. an axp288 PMIC.
> 
> I plan to write some patches for drivers accessing the PMIC bus to
> limit their bus accesses to a bare minimum (e.g. cache registers, do not
> update battery level more often then 4 times a minute), to limit the
> amount of wakeups.
> 
> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=155241
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> Tested-by: tagorereddy <tagore.chandan@gmail.com>
> ---
> Changes in v2:
> -Spelling: P-Unit, PMIC
> ---
>  drivers/gpu/drm/i915/i915_drv.h     |  1 +
>  drivers/gpu/drm/i915/intel_uncore.c | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index c717329..52f7dde 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -721,6 +721,7 @@ struct intel_uncore {
>  	const struct intel_forcewake_range *fw_domains_table;
>  	unsigned int fw_domains_table_entries;
>  
> +	struct notifier_block pmic_bus_access_nb;
>  	struct intel_uncore_funcs funcs;
>  
>  	unsigned fifo_count;
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 3767307..175fe02 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -25,6 +25,7 @@
>  #include "intel_drv.h"
>  #include "i915_vgpu.h"
>  
> +#include <asm/iosf_mbi.h>
>  #include <linux/pm_runtime.h>
>  
>  #define FORCEWAKE_ACK_TIMEOUT_MS 50
> @@ -429,12 +430,16 @@ static void __intel_uncore_early_sanitize(struct drm_i915_private *dev_priv,
>  
>  void intel_uncore_suspend(struct drm_i915_private *dev_priv)
>  {
> +	iosf_mbi_unregister_pmic_bus_access_notifier(
> +		&dev_priv->uncore.pmic_bus_access_nb);
>  	__intel_uncore_forcewake_reset(dev_priv, false);
>  }
>  
>  void intel_uncore_resume(struct drm_i915_private *dev_priv)
>  {
>  	__intel_uncore_early_sanitize(dev_priv, true);
> +	iosf_mbi_register_pmic_bus_access_notifier(
> +		&dev_priv->uncore.pmic_bus_access_nb);
>  	i915_check_and_clear_faults(dev_priv);
>  }

The early/normal/late suspend/resume ordering starts to bother me a
little more now. I wonder if we're totally safe wrt. the suspend/resume
order of the devices now.

> @@ -1390,6 +1395,28 @@ static void intel_uncore_fw_domains_init(struct drm_i915_private *dev_priv)
>  	dev_priv->uncore.fw_domains_table_entries = ARRAY_SIZE((d)); \
>  }
>  
> +static int i915_pmic_bus_access_notifier(struct notifier_block *nb,
> +					 unsigned long action, void *data)
> +{
> +	struct drm_i915_private *dev_priv = container_of(nb,
> +			struct drm_i915_private, uncore.pmic_bus_access_nb);
> +
> +	switch (action) {
> +	case MBI_PMIC_BUS_ACCESS_BEGIN:
> +		/*
> +		 * forcewake all to make sure that we don't need to forcewake
> +		 * any power-planes while the pmic bus is busy.
> +		 */
> +		intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);

I must say I don't really like this stuff at all. But if it helps I gues
we should go for it. I'd like to see the comment elaborate a bit more on
why we think it's is needed.

> +		break;
> +	case MBI_PMIC_BUS_ACCESS_END:
> +		intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
> +		break;
> +	}
> +
> +	return NOTIFY_OK;
> +}
> +
>  void intel_uncore_init(struct drm_i915_private *dev_priv)
>  {
>  	i915_check_vgpu(dev_priv);
> @@ -1399,6 +1426,8 @@ void intel_uncore_init(struct drm_i915_private *dev_priv)
>  	__intel_uncore_early_sanitize(dev_priv, false);
>  
>  	dev_priv->uncore.unclaimed_mmio_check = 1;
> +	dev_priv->uncore.pmic_bus_access_nb.notifier_call =
> +		i915_pmic_bus_access_notifier;
>  
>  	switch (INTEL_INFO(dev_priv)->gen) {
>  	default:
> @@ -1458,6 +1487,9 @@ void intel_uncore_init(struct drm_i915_private *dev_priv)
>  		ASSIGN_READ_MMIO_VFUNCS(vgpu);
>  	}
>  
> +	iosf_mbi_register_pmic_bus_access_notifier(
> +		&dev_priv->uncore.pmic_bus_access_nb);
> +
>  	i915_check_and_clear_faults(dev_priv);
>  }
>  #undef ASSIGN_WRITE_MMIO_VFUNCS
> @@ -1465,6 +1497,9 @@ void intel_uncore_init(struct drm_i915_private *dev_priv)
>  
>  void intel_uncore_fini(struct drm_i915_private *dev_priv)
>  {
> +	iosf_mbi_unregister_pmic_bus_access_notifier(
> +		&dev_priv->uncore.pmic_bus_access_nb);
> +
>  	/* Paranoia: make sure we have disabled everything before we exit. */
>  	intel_uncore_sanitize(dev_priv);
>  	__intel_uncore_forcewake_reset(dev_priv, false);
> -- 
> 2.9.3

-- 
Ville Syrjälä
Intel OTC
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