[RFC PATCH v2 13/17] gpu: host1x: Reset max value when freeing a syncpoint

[Mikko Perttunen]

On 9/16/20 10:44 PM, Dmitry Osipenko wrote:
> 05.09.2020 13:34, Mikko Perttunen пишет:
>> With job recovery becoming optional, syncpoints may have a mismatch
>> between their value and max value when freed. As such, when freeing,
>> set the max value to the current value of the syncpoint so that it
>> is in a sane state for the next user.
>>
>> Signed-off-by: Mikko Perttunen <mperttunen at nvidia.com>
>> ---
>>   drivers/gpu/host1x/syncpt.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/gpu/host1x/syncpt.c b/drivers/gpu/host1x/syncpt.c
>> index 2fad8b2a55cc..82ecb4ac387e 100644
>> --- a/drivers/gpu/host1x/syncpt.c
>> +++ b/drivers/gpu/host1x/syncpt.c
>> @@ -385,6 +385,7 @@ static void syncpt_release(struct kref *ref)
>>   {
>>   	struct host1x_syncpt *sp = container_of(ref, struct host1x_syncpt, ref);
>>   
>> +	atomic_set(&sp->max_val, host1x_syncpt_read_min(sp));
>>   	sp->locked = false;
>>   
>>   	mutex_lock(&sp->host->syncpt_mutex);
>>
> 
> Please note that the sync point state actually needs to be completely
> reset at the sync point request-time because both downstream fastboot
> and upstream u-boot [1] are needlessly enabling display VBLANK interrupt
> that continuously increments sync point #26 during of kernel boot until
> display controller is reset.
> 
> [1] https://github.com/u-boot/u-boot/blob/master/drivers/video/tegra.c#L155
> 
> Hence once sync point #26 is requested, it will have a dirty state. So
> far this doesn't have any visible effect because sync points aren't used
> much.
> 

Maybe we can instead reserve syncpoints that might be used by the boot 
chain, and only allow allocating them once the display driver has acked 
that the syncpoint will no longer be incremented? That way if the 
display driver is disabled for some reason we'll still be fine.

Looking at the downstream driver, it (still, on new chips..) reserves 
the following syncpoints:

- 10 (AVP)
- 22 (3D)
- 26 (VBLANK0)
- 27 (VBLANK1)

and says that this applies to T20, T30, T114 and T148.

I suppose if you haven't observed this happening to other syncpoints 
than 26, then reserving 26 would probably be enough.

Mikko