On Wed, Jul 11, 2012 at 6:05 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> On Wed, Jul 11, 2012 at 3:24 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
>
>> If we *do* want to change something there, I don't like the proposal
>> above any better. It's still basically saying "presence detect is
>> only reliable when X is set" when X is not clearly related to presence
>> detect.
>>
>> I think it's better to disable the presence detect interrupt
>> completely if it's not reliable, as your original patch did. My
>> complaint with that is that HP_SUPR_RM() doesn't seem like the right
>> test for "the interrupt is not reliable."
>
> ok.
>
>>
>> Having a "Presence Detect State" bit and an interrupt that tells you
>> when it changed is only meaningful if that bit gives you useful
>> information. If hardware supplies that bit but it toggles all the
>> time when the slot is empty because it's hooked up to link training
>> attempts, that just means the hardware screwed up. The hardware
>> *should* have included some logic to filter out the attempts and
>> toggle the bit only when a card is actually added or removed. I
>> believe the functionality of "Presence Detect State" is logically
>> independent of "Hot-Plug Surprise" and "Attention Button Present."
>
> the cpu vendor already agreed that is out of spec for that.
>
>>
>> So if we want to disable the "Presence Detect Changed" interrupt,
>> that's fine, but I think we should do it based on a quirk or
>> blacklist, or based on the fact that we have no need for it. One
>> reason to want the interrupt is if "Hot-Plug Surprise" is set,
>> indicating that an adapter might be removed without notice, and if
>> that's the only reason, we could use your original patch.
>
> no, with that patch, we will not get interrupt for present bit change
> for non-hotplug-surprise
> case.
>
>> But if we
>> do, I think we should change interrupt_event_handler() to look
>> something like this:
>>
>> case INT_PRESENCE_ON:
ctrl_info(ctrl, "adapter now present\n");
>> if (!ATTN_BUTTN(ctrl))
>> handle_surprise_event(p_slot); /* omit this if you don't
>> think it's useful */
>> break;
>> case INT_PRESENCE_OFF:
ctrl_warn(ctrl, "adapter removed unexpectedly\n");
>> handle_surprise_event(p_slot);
>> break;
>
> yes, this one should be good. and it is enhancement.
When we don't have an attention button, I don't know that it's a good
idea to automatically power up a new card. I was thinking about
things like ExpressCard, where the standard usage model probably *is*
"plug in the card and it automatically starts working, no button press
or software UI required." But my guess is that ExpressCard would not
be handled by pciehp, would it?
The pciehp flow seems to be basically the same as SHPC, and the
Standard Hot-Plug Controller spec, rev 1.0, sec 2.5, has a flow of
hot-add without an attention button. It shows:
1) User selects empty, disabled slot and opens MRL
2) Adapter insertion:
2a) User inserts add-in-card
2b) User closes MRL
2c) User attaches cables
3) User requests via software UI that slot be enabled
We'll get the Presence Detect interrupt at step 2a, before the user
can close the MRL or attach cables. I don't know if it's a good thing
to power-on the slot and attach the driver while this is happening.
It certainly doesn't seem to follow the intent of the spec.
>> If you did make a change like this, I propose (as a separate patch)
>> passing info->event_type into handle_surprise_event(). We've already
>> read the "Presence Detect State" bit, so there's no need for
>> handle_surprise_event() to do it again.
>
> ok. will prepare patches for that.
>
> Yinghai
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