Re: [PATCH] drm/exynos: resolve infinite loop issue on non multi-platform

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

On 2014년 11월 07일 17:29, Andrzej Hajda wrote:
> On 11/06/2014 03:10 PM, Inki Dae wrote:
>> This patch resovles the infinite loop issue incurred
>> when Exyno drm driver is enabled but all kms drivers
>> are disabled on Exynos board by returning -EPROBE_DEFER
>> only in case that there is kms device registered.
> 
> There are many different cases it can still fail:
> - there are no matching device nodes in DT,

With this patch, -ENODEV would be returned instead of -EPROBE_DEFER in
above case. So it should be no problem.

> - some devices are present in DT, some drivers are enabled,
> but they do not match,

Right.

> - even if there exists some pairs device_node-driver it can fail -
> exynos_drm_match_add requires higher level matches - every crtc should
> have matching encoder.

Also right.

> 
> I think even super-node will not solve all these issues.
> 

With the super device node, my intention is that we can remove
unnecessary exception codes like of_machine_is_compatible functions. So
the use of the super device node wouldn't be relevant to this issue.

> The real problem here is that during probe of exynos_drm ipp driver is
> successfully probed and after that exynos_drm probe fails, which causes
> also removing ipp, anyway successful ipp probe triggers whole re-probe
> mechanism again. It creates infinite loop.

The problem is not because of only IPP driver. In all cases that non kms
drivers are enabled and they are probed.

> 
> I think moving exynos_platform_device_ipp_register after
> component_master_add_with_match should solve some of the issue,

g2d also should be moved.

> but I guess it could create new ones, or maybe not, needs checking.
> 
> On the other side I wonder if we really need to have ipp device at all,
> replacing it with helpers of exynos_drm should be possible, I guess.
> 

Agree. I also think that we don't really need IPP driver. Instead, we
can register post processor drivers - fimc, rotator, and gscaler -
directly without IPP driver like g2d did.

Thanks,
Inki Dae

> Regards
> Andrzej
> 
>>
>> Signed-off-by: Inki Dae <inki.dae@samsung.com>
>> ---
>>  drivers/gpu/drm/exynos/exynos_drm_drv.c |    6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.c b/drivers/gpu/drm/exynos/exynos_drm_drv.c
>> index ecc86aa..14c6af7 100644
>> --- a/drivers/gpu/drm/exynos/exynos_drm_drv.c
>> +++ b/drivers/gpu/drm/exynos/exynos_drm_drv.c
>> @@ -488,6 +488,12 @@ static struct component_match *exynos_drm_match_add(struct device *dev)
>>  
>>  	mutex_lock(&drm_component_lock);
>>  
>> +	/* Do not retry to probe if there is no any kms driver regitered. */
>> +	if (list_empty(&drm_component_list)) {
>> +		mutex_unlock(&drm_component_lock);
>> +		return ERR_PTR(-ENODEV);
>> +	}
>> +
>>  	list_for_each_entry(cdev, &drm_component_list, list) {
>>  		/*
>>  		 * Add components to master only in case that crtc and
>>
> 
> 
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