RE: 3 EC issues

[Zheng, Lv]

Hi,

I just made a freak change to let reporters to try.
https://bugzilla.kernel.org/attachment.cgi?id=178271&action=diff
I'll report back after seeing their test results.

Thanks and best regards
-Lv

> From: Zheng, Lv
> Sent: Wednesday, May 27, 2015 1:57 PM
> 
> Hi,
> 
> Let me Cc intel power management and ACPI mailing list to discuss this widely.
> 
> On Samsung platforms, test result shows when SCI_EVT is not set, a QR_EC can result in a real event value (non-0x00) returned.
> And after system is resumed, SCI_EVT may not be flagged while OSPM still need to send QR_EC.
> We have an EC_FLAGS_CLEAR_ON_RESUME quirk to handle this.
> 
> On kernel Bugzilla reported platforms (Lenovo, Acer), firmware will stop responding occasionally if SCI_EVT is not set.
> We have an EC_FLAGS_QUERY_HANDSHAKE quirk to handle them.
> 
> It looks to me the 2 behavior is conflict.
> For Samsung, QR_EC need to be issued even when SCI_EVT is not set.
> While for the latter platforms, QR_EC shouldn't be issued if SCI_EVT is not set.
> 
> Also IMO, the EC_FLAGS_QUERY_HANDSHAKE platforms are dangerous, it looks their firmware will be more likely to get stuck as the
> SCI_EVT behavior is not standardized.
> 
> Unlike the EC transaction state machine, it is hardly to write a single state machine to control the conflict behavior.
> Thus I have to guess Windows just handle the SCI_EVT in a specific way that happens to work for both cases.
> 
> To handle SCI_EVT, OSPM should know when the SCI_EVT will be cleared by the firmware.
> 
> Unfortunately, the ACPI specification only has following 2 paragraphs talking SCI_EVT and none of them has defined this:
> 
> 12.2.1 Embedded Controller Status, EC_SC (R)
> The SCI event (SCI_EVT) flag is set when the embedded controller has detected an internal event that requires the operating system's
> attention. The embedded controller sets this bit in the status register, and generates an SCI to OSPM. OSPM needs this bit to
> differentiate command-complete SCIs from notification SCIs. OSPM uses the query command to request the cause of the SCI_EVT
> and take action. For more information, see Section 12.3, "Embedded Controller Command Set.")
> 
> 12.3.5 Query Embedded Controller, QR_EC (0x84)
> OSPM driver sends this command when the SCI_EVT flag in the EC_SC register is set. When the embedded controller has detected a
> system event that must be communicated to OSPM, it first sets the SCI_EVT flag in the EC_SC register, generates an SCI, and then
> waits for OSPM to send the query (QR_EC) command. OSPM detects the embedded controller SCI, sees the SCI_EVT flag set, and
> sends the query command to the embedded controller. Upon receipt of the QR_EC command byte, the embedded controller places a
> notification byte with a value between 0-255, indicating the cause of the notification. The notification byte indicates which interrupt
> handler operation should be executed by OSPM to process the embedded controller SCI. The query value of zero is reserved for a
> spurious query result and indicates "no outstanding event."
> 
> None of them has definitions around the timing that the SCI_EVT should be cleared.
> Following may be possible (from earliest to latest, and should be initiated from a firmware step):
>   1. After firmware noticing an EC_SC access - since OSPM should have seen the SCI_EVT.
>   2. After firmware noticing an none-empty input pipe filled with QR_EC - since OSPM has explicitly acknowledged the event by the
> QR_EC command.
>   3. After firmware writing the event value to the output pipe - since OSPM is ensured to see the returned event value to query.
>   4. After firmware noticing an empty output pipe - since OSPM is ensured to have obtained the returned event value to query.
>   5. After OSPM evaluating _Qxx - EVT_SCI may be implemented in the "condition" way and cleared after the condition has been
> changed.
> 
> In order to handle both firmware variation, Windows should have prepared QR_EC in the way that
> 1. can ensure additional QR_EC is issued for Samsung - when the SCI_EVT is checked again, it should have still be flagged so that a
> "draining QR_EC" can be issued.
> 2. can ensure no additional QR_EC is issued for Lenovo/Acer - when the SCI_EVT is checked again, it must be cleared by the firmware.
> 
> So if we can know the expected behavior of Windows, we may be able to work out the correct solution.
> 
> Thanks and best regards
> -Lv
> 
> 
> > From: Wysocki, Rafael J
> > Sent: Saturday, May 23, 2015 8:32 AM
> >
> > Len,
> >
> > It appears that we need to know what the Windows EC driver expects from
> > the firmware.
> >
> > Who's the first point of contact for that?
> >
> > Rafael
> >
> >
> > On 5/22/2015 9:33 AM, Zheng, Lv wrote:
> > > Hi, Bob and Rafael
> > >
> > > I have 3 ACPI bugs related to the EC event handling mechanism.
> > >
> > > https://bugzilla.kernel.org/show_bug.cgi?id=98111
> > > https://bugzilla.kernel.org/show_bug.cgi?id=97381
> > > https://bugzilla.kernel.org/show_bug.cgi?id=94411
> > >
> > > So it might be urgent to handle them.
> > >
> > > Currently the EC driver checks EVT_SCI flag right after QR_EC write so that EVT_SCI can be ensured to be set for Samsung
> platforms
> > and the 2nd QR_EC can be issued to drain the event (on Samsung platform, 0x00 will be returned to indicate no further events). This
> > logic is tricky.
> > >
> > > After seeing so many conflicts, I guess windows will start a deferred context to send QR_EC, evaluate _Qxx sequentially.
> > > For Samsung platform, I knew an 0x00 return value of QR_EC can terminate the process and Samsung platform really need driver
> to
> > poll until 0x00 is returned.
> > >
> > > But on other platforms, we may see non 0x00 value returned from BIOS, then I don't know how can I terminate the process on
> such
> > platforms.
> > >
> > > IMO, the conflict is there due to the asynchrony the firmware has implemented.
> > > It looks the firmware that won't be broken due to our current behavior is handled in the fully asynchronous way.
> > > And the above platforms have several commands handled in the synchronous way.
> > >
> > > Thus it's hard for me to determine what's the preferred behavior (thus the default OS EC driver behavior) Windows EC driver has
> > expected on the firmware.
> > > Do we have spec contact or Windows contact to clarify this?
> > >
> > > Thanks and best regards
> > > -Lv

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