Re: [PATCH] drm/exynos: fix infinite loop issue incurred by no pair

[Inki Dae <inki.dae@samsung.com>]

On 2014년 11월 18일 16:58, Sjoerd Simons wrote:
> On Tue, 2014-11-18 at 12:20 +0900, Inki Dae wrote:
>> This patch makes the deferred probe is tried up to 3 times in maximum.
>> However, this is considered only for Exynos drm so I think other SoC
>> drivers could also produce same issue. Therefore, the best way to resolve
>> this issue, infinite loop incurred by defered probe, would be that dd core
>> is fixed up corrrectly.
> 
> At first sight this seems to make little to no sense. Unless i'm
> mistaken this would cause the exynos drm probe return -ENODEV to the dd
> core, causing it to stop trying to probe. Which obviously breaks your
> infinite loop, it also breaks situations where the probe needs to be
> retried more then 3 times. 

Right, but at least, we could avoid kernel booting failure which is very
critical. Please know that this patch is temporary to avoid the kernel
booting failure although deferred probe request of Exynos drm could be
broken. For this, I will look into dd core to find out more generic way:
I suspect that this might be incurred in case that a driver is probed in
probe context of other driver or it might be really dd core bug.

Thanks,
Inki Dae

> 
> I suspect with this patch once exynos DRM is loaded and actually validly
> needs to defer (iotw when the required modules do exist but simply
> aren't loaded just yet), it still jumps into an infinite loop which you
> break after 3 tries after which the display will simply never come up
> even if everything is in place because the core doesn't know it should
> re-probe....
> 
> 
> 
>> Signed-off-by: Inki Dae <inki.dae@samsung.com>
>> ---
>>  drivers/gpu/drm/exynos/exynos_drm_drv.c |    8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.c b/drivers/gpu/drm/exynos/exynos_drm_drv.c
>> index eab12f0..4d84f3a 100644
>> --- a/drivers/gpu/drm/exynos/exynos_drm_drv.c
>> +++ b/drivers/gpu/drm/exynos/exynos_drm_drv.c
>> @@ -38,6 +38,8 @@
>>  #define DRIVER_MAJOR	1
>>  #define DRIVER_MINOR	0
>>  
>> +#define MAX_TRY_PROBE_DEFER	3
>> +
>>  static struct platform_device *exynos_drm_pdev;
>>  
>>  static DEFINE_MUTEX(drm_component_lock);
>> @@ -481,6 +483,7 @@ static struct component_match *exynos_drm_match_add(struct device *dev)
>>  	struct component_match *match = NULL;
>>  	struct component_dev *cdev;
>>  	unsigned int attach_cnt = 0;
>> +	static unsigned int try_probe_defer;
>>  
>>  	mutex_lock(&drm_component_lock);
>>  
>> @@ -527,6 +530,11 @@ out_lock:
>>  
>>  	mutex_unlock(&drm_component_lock);
>>  
>> +	if (++try_probe_defer > MAX_TRY_PROBE_DEFER) {
>> +		try_probe_defer = 0;
>> +		return ERR_PTR(-ENODEV);
>> +	}
>> +
>>  	return attach_cnt ? match : ERR_PTR(-EPROBE_DEFER);
>>  }
>>  
> 
>