On 11/06/2014 06:08 PM, Sjoerd Simons wrote:
> On Thu, 2014-11-06 at 23:10 +0900, 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.
>
> It would be nice if you could explain in the commit message/comment why
> returning -EPROBE_DEFER causes an infinite loop and why it's the wrong
> thing to do in this case?
>
> Even if you know this probe will never succeed in the future (so
> deferring is actually pointless), deferring really shouldn't trigger
> infinte loops in calling code
>
+CC: Grant and Greg
It seems to be partly an issue with deferred probing. I guess it affects
all drivers which in their probe can cause successful probe of
sub-driver/sub-device, and after that the main driver defers probing,
unwinding changes including removal of sub-driver/sub-device. Driver
core incorrectly re-triggers probing in this case.
In this particular case it could be fixed in exynos_drm driver I guess,
but maybe it would be good to fix deferred probing, if possible.
Regards
Andrzej
>>
>> Signed-off-by: Inki Dae <inki.dae@xxxxxxxxxxx>
>> ---
>> 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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