Messages in this thread | | | Date | Fri, 21 May 2021 08:21:58 -0700 | From | khsieh@codeauro ... | Subject | Re: [PATCH v4 1/2] drm/msm/dp: handle irq_hpd with sink_count = 0 correctly |
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On 2021-05-20 22:00, Stephen Boyd wrote: > Quoting khsieh@codeaurora.org (2021-05-20 15:39:09) >> On 2021-05-20 14:28, Stephen Boyd wrote: >> > Quoting khsieh@codeaurora.org (2021-05-20 13:05:48) >> >> On 2021-05-20 12:28, Stephen Boyd wrote: >> >> >> Put dongle to D3 state so that it will not issue the unnecessary >> >> >> second >> >> >> irq_hpd with sink_count = 0. this will prevent the annoy but unharmful >> >> >> DP_LINK_STATUS_UPDATED warning message. >> >> >> Again, we can not disable hpd interrupt since dongle still attached >> >> >> and >> >> >> hdmi cable can be plugged in at any instant. >> >> >> >> >> > >> >> > Right I'm not suggesting to disable hpd interrupt, just the hpd_irq >> >> > interrupt once an unplug irq comes in, and do that in hardirq context. >> >> > Also, I'm suggesting that we consider unplug as a higher priority if >> >> > the >> >> > hard irq handler is delayed for some reason and both an unplug irq and >> >> > an hpd irq are pending in the hardware when the hard irq handler is >> >> > running. Putting the dongle into D3 state won't fix these problems. >> >> >> >> >> >> >> >> The unplug interrupt is not happen in this case since dongle still >> >> attached. >> >> The unplug interrupt only happen when dongle unplugged. >> > >> > Agreed. >> > >> >> >> >> I think you mistakenly think DP_LINK_STATUS_UPDATED is caused by >> >> unplug >> >> interrupt. >> > >> > Ok, got it. >> > >> >> DP_LINK_STATUS_UPDATED happen is due to dongle issue two consecutive >> >> irq_hpd with sink_count = 0 when hdmi cable unplugged from dongle. >> >> The first irq_hpd with sink_count = 0 is handled as expected to turn >> >> off >> >> display. >> >> After that the second irq_hpd with sink_count = 0 is handled. >> >> Since display had turned off, then there is nothing to do but spill >> >> DP_LINK_STATUS_UPDATED warning message. >> >> There is no unplug (hpd become low) happen in this case since dongle >> >> still attached. >> > >> > Agreed. >> > >> >> >> >> All interrupt (plug/irq_hpd and unplug) are required to be handled in >> >> the order of happening. >> >> We can not ignore any one. >> >> For example, you plug/unplug two different resolution monitor >> >> alternative to/from dongle and unplug dongle once for while. >> >> >> >> I think the race condition you describe here all had been taken care >> >> with >> >> 1) convert irq into event and store at event q in order. >> >> 2) irq handled base on transaction. Next irq can be handled when >> >> previous irq transaction is done. >> >> >> > >> > I'm mostly trying to point out that the irq handling and masking needs >> > to be done in the hard irq context and not in the kthread. It may or >> > may >> > not be related to this message that's printed. >> > >> > What happens if the hardirq is blocked by some other irq that takes a >> > long time to process? Imagine this scenario: >> > >> > CPU0 CPU1 >> > ---- ---- >> > really_long_other_hardirq() { >> > hpd_irq >> > hpd_irq >> > hpd low >> > } >> > >> > dp_display_irq_handler() { >> > >> >> >> > <fork things to kthread> >> > } >> > >> > Shouldn't we ignore any hpd_irq events in this scenario? And shouldn't >> > we be disabling the hpd_irq by masking it with DP_DP_IRQ_HPD_INT_MASK >> > when hpd goes low (i.e. DP_DP_HPD_UNPLUG_INT_MASK)? >> >> >> >> 1) irq_hpd interrupt always happen before unplug interrupt >> 2)if hdp_isr_status = (DP_DP_IRQ_HPD_INT_MASK | >> DP_DP_HPD_UNPLUG_INT_MASK) at the time when read at >> dp_display_irq_handler(), >> then DP_DP_IRQ_HPD_INT_MASK will be add into evetn q first followed by >> DP_DP_HPD_UNPLUG_INT_MASK be add into event q. >> So that DP_DP_IRQ_HPD_INT_MASK will be executed by the event thread >> before DP_DP_HPD_UNPLUG_INT_MASK. >> On the other word, IRQ_HPD has higher priority over UNPLUG in the >> timing >> matter. >> By doing that we can shut down display gracefully. > > Ok. So you're saying that we want to put both events on the queue > regardless, and put IRQ_HPD there first because we want to check the > status bit? Doesn't reading the status bit require the dongle to be > connected though? So if an unplug came in along with an irq_hpd we may > queue both the irq_hpd and the unplug, but when it comes time to > process > the irq_hpd in the kthread the link will be gone and so trying the dpcd > read for the link status will fail? > yes, we had a previous bug with this scenarios already. https://partnerissuetracker.corp.google.com/issues/170598152 At this case, dongle produce two interrupts, irq_hpd followed by unplug immediately (not presented at isr status register at same time), at the time dongle unplugged form DTU. But due to dp ctrl reset at handling irq_hpd which cause unplug mask bit be cleared so that unplug interrupt got lost.
I think V6 patch is good to go.
>> >> If you insist, at hdp_isr_status = (DP_DP_IRQ_HPD_INT_MASK | >> DP_DP_HPD_UNPLUG_INT_MASK) case, >> we can have only add DP_DP_HPD_UNPLUG_INT_MASK to event q only by >> dropping DP_DP_IRQ_HPD_INT_MASK. >> Is this will work for you? >> > > I'm not insisting on anything. I'm just trying to think of various > corner cases that we're not handling in the code so we don't have to > worry about them in the future.
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