Re: [PATCH 01/42] drm/omap: fix suspend/resume handling

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 07/03/16 09:52, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Monday 22 February 2016 19:10:07 Tomi Valkeinen wrote:
>> For legacy reasons omapdss handles system suspend/resume via PM notifier
>> callback, where the driver disables/resumes all the outputs.
>>
>> This doesn't work well with omapdrm. What happens on suspend is that the
>> omapdss disables the displays while omapdrm is still happily continuing
>> its work, possibly waiting for an vsync irq, which will never come if
>> the display output is disabled, leading to timeouts and errors sent to
>> userspace.
>>
>> This patch moves the suspend/resume handling to omapdrm, and the
>> suspend/resume is now done safely inside modeset lock.
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
>> ---
>>  drivers/gpu/drm/omapdrm/dss/core.c    | 29 -----------------------
>>  drivers/gpu/drm/omapdrm/dss/display.c | 36 ----------------------------
>>  drivers/gpu/drm/omapdrm/dss/dss.h     |  2 --
>>  drivers/gpu/drm/omapdrm/omap_drv.c    | 44 ++++++++++++++++++++++++++++++++
>>  4 files changed, 44 insertions(+), 67 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/omapdrm/dss/core.c
>> b/drivers/gpu/drm/omapdrm/dss/core.c index 54eeb507f9b3..1f55d0aae03d
>> 100644
>> --- a/drivers/gpu/drm/omapdrm/dss/core.c
>> +++ b/drivers/gpu/drm/omapdrm/dss/core.c
>> @@ -165,31 +165,6 @@ int dss_debugfs_create_file(const char *name, void
>> (*write)(struct seq_file *)) #endif /* CONFIG_OMAP2_DSS_DEBUGFS */
>>
>>  /* PLATFORM DEVICE */
>> -static int omap_dss_pm_notif(struct notifier_block *b, unsigned long v,
>> void *d) -{
>> -	DSSDBG("pm notif %lu\n", v);
>> -
>> -	switch (v) {
>> -	case PM_SUSPEND_PREPARE:
>> -	case PM_HIBERNATION_PREPARE:
>> -	case PM_RESTORE_PREPARE:
>> -		DSSDBG("suspending displays\n");
>> -		return dss_suspend_all_devices();
>> -
>> -	case PM_POST_SUSPEND:
>> -	case PM_POST_HIBERNATION:
>> -	case PM_POST_RESTORE:
>> -		DSSDBG("resuming displays\n");
>> -		return dss_resume_all_devices();
>> -
>> -	default:
>> -		return 0;
>> -	}
>> -}
>> -
>> -static struct notifier_block omap_dss_pm_notif_block = {
>> -	.notifier_call = omap_dss_pm_notif,
>> -};
>>
>>  static int __init omap_dss_probe(struct platform_device *pdev)
>>  {
>> @@ -211,8 +186,6 @@ static int __init omap_dss_probe(struct platform_device
>> *pdev) else if (pdata->default_device)
>>  		core.default_display_name = pdata->default_device->name;
>>
>> -	register_pm_notifier(&omap_dss_pm_notif_block);
>> -
>>  	return 0;
>>
>>  err_debugfs:
>> @@ -222,8 +195,6 @@ err_debugfs:
>>
>>  static int omap_dss_remove(struct platform_device *pdev)
>>  {
>> -	unregister_pm_notifier(&omap_dss_pm_notif_block);
>> -
>>  	dss_uninitialize_debugfs();
>>
>>  	return 0;
>> diff --git a/drivers/gpu/drm/omapdrm/dss/display.c
>> b/drivers/gpu/drm/omapdrm/dss/display.c index ef5b9027985d..24c2bffa0036
>> 100644
>> --- a/drivers/gpu/drm/omapdrm/dss/display.c
>> +++ b/drivers/gpu/drm/omapdrm/dss/display.c
>> @@ -78,42 +78,6 @@ void omapdss_default_get_timings(struct omap_dss_device
>> *dssdev, }
>>  EXPORT_SYMBOL(omapdss_default_get_timings);
>>
>> -int dss_suspend_all_devices(void)
>> -{
>> -	struct omap_dss_device *dssdev = NULL;
>> -
>> -	for_each_dss_dev(dssdev) {
>> -		if (!dssdev->driver)
>> -			continue;
>> -
>> -		if (dssdev->state == OMAP_DSS_DISPLAY_ACTIVE) {
>> -			dssdev->driver->disable(dssdev);
>> -			dssdev->activate_after_resume = true;
>> -		} else {
>> -			dssdev->activate_after_resume = false;
>> -		}
>> -	}
>> -
>> -	return 0;
>> -}
>> -
>> -int dss_resume_all_devices(void)
>> -{
>> -	struct omap_dss_device *dssdev = NULL;
>> -
>> -	for_each_dss_dev(dssdev) {
>> -		if (!dssdev->driver)
>> -			continue;
>> -
>> -		if (dssdev->activate_after_resume) {
>> -			dssdev->driver->enable(dssdev);
>> -			dssdev->activate_after_resume = false;
>> -		}
>> -	}
>> -
>> -	return 0;
>> -}
>> -
>>  void dss_disable_all_devices(void)
>>  {
>>  	struct omap_dss_device *dssdev = NULL;
>> diff --git a/drivers/gpu/drm/omapdrm/dss/dss.h
>> b/drivers/gpu/drm/omapdrm/dss/dss.h index 9a6453235585..a974d46672db 100644
>> --- a/drivers/gpu/drm/omapdrm/dss/dss.h
>> +++ b/drivers/gpu/drm/omapdrm/dss/dss.h
>> @@ -206,8 +206,6 @@ int dss_set_min_bus_tput(struct device *dev, unsigned
>> long tput); int dss_debugfs_create_file(const char *name, void
>> (*write)(struct seq_file *));
>>
>>  /* display */
>> -int dss_suspend_all_devices(void);
>> -int dss_resume_all_devices(void);
>>  void dss_disable_all_devices(void);
>>
>>  int display_init_sysfs(struct platform_device *pdev);
>> diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c
>> b/drivers/gpu/drm/omapdrm/omap_drv.c index dfafdb602ad2..e21433c3fda4
>> 100644
>> --- a/drivers/gpu/drm/omapdrm/omap_drv.c
>> +++ b/drivers/gpu/drm/omapdrm/omap_drv.c
>> @@ -900,12 +900,52 @@ static int pdev_remove(struct platform_device *device)
>> }
>>
>>  #ifdef CONFIG_PM_SLEEP
>> +static int omap_drm_suspend_all_displays(void)
>> +{
>> +	struct omap_dss_device *dssdev = NULL;
>> +
>> +	for_each_dss_dev(dssdev) {
>> +		if (!dssdev->driver)
>> +			continue;
>> +
>> +		if (dssdev->state == OMAP_DSS_DISPLAY_ACTIVE) {
>> +			dssdev->driver->disable(dssdev);
>> +			dssdev->activate_after_resume = true;
>> +		} else {
>> +			dssdev->activate_after_resume = false;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int omap_drm_resume_all_displays(void)
>> +{
>> +	struct omap_dss_device *dssdev = NULL;
>> +
>> +	for_each_dss_dev(dssdev) {
>> +		if (!dssdev->driver)
>> +			continue;
>> +
>> +		if (dssdev->activate_after_resume) {
>> +			dssdev->driver->enable(dssdev);
>> +			dssdev->activate_after_resume = false;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  static int omap_drm_suspend(struct device *dev)
>>  {
>>  	struct drm_device *drm_dev = dev_get_drvdata(dev);
>>
>>  	drm_kms_helper_poll_disable(drm_dev);
>>
>> +	drm_modeset_lock_all(drm_dev);
> 
> The omapdss implementation of the suspend and resume handlers didn't take the 
> modeset locks. I wonder what we're trying to protect against here, what other 
> concurrent task(s) could race us ?

The description explains at least one case I was encountering. To be
honest, the new code doesn't feel very good either, but at least the
entry point is now in omapdrm, and protected with a lock, so it should
be much safer.

As for what else is there... I hope not much. The panel/encoder drivers
can execute code in an interrupt or possibly even via a sysfs file if
someone would add things like that, and at the moment we don't have
means to properly deal with it. But afaik the current drivers don't do
any of those.

 Tomi


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