[Intel-gfx] [DMC_BUGFIX_SKL_V2 1/5] drm/i915/skl: Added a check for the hardware status of csr fw before loading.

Daniel Vetter daniel at ffwll.ch
Wed Sep 30 05:14:04 PDT 2015

On Wed, Sep 30, 2015 at 02:50:40AM +0200, Rafael J. Wysocki wrote:
> On 9/29/2015 10:51 AM, Daniel Vetter wrote:
> >On Tue, Sep 29, 2015 at 01:54:53AM +0200, Rafael J. Wysocki wrote:
> >>On 9/28/2015 8:52 AM, Daniel Vetter wrote:
> >>>On Wed, Sep 23, 2015 at 10:49:36PM +0200, Rafael J. Wysocki wrote:
> >>>>On 9/23/2015 7:17 PM, Daniel Vetter wrote:
> >>>>>acpi_target_system_state() seems to be almost the thing we're looking
> >>>>>for, except that it's only valid in the suspend callbacks since it
> >>>>>gets reset to ACPI_STATE_S0 when resuming. So probably we want
> >>>>>something else ...
> >>>>Right.
> >>>>
> >>>>The idea is to add a way for drivers to check if
> >>>>(a) suspend is going to enter the BIOS
> >>>>(b) resume has been triggered by the BIOS
> >>>>and that's really what drivers need to know.
> >>>>
> >>>>For suspend-to-idle those two will return false and for S3 they'll return
> >>>>true.
> >>>>
> >>>>Would that help?
> >>>Not sure that matches exaxtly what we'd need here ... Essentially we need
> >>>to know whether we've been in S3/S4 (firmware has been eaten) or in one of
> >>>the higher suspend-to-idle/standby states (firmware still alive, don't
> >>>disturb it). Additional fun that just crossed my mind is that if the
> >>>suspend-to-mem is aborted (some other driver failed) then that function
> >>>should _not_ indicate that we've been in S3. So maybe something like
> >>So it really looks like the interface I was talking about would be suitable:
> >>
> >>pm_suspend_via_firmware() == true -> firmware is going to be eaten (use that
> >>during suspend if needed)
> >>pm_resume_via_firmware() == true -> firmware was eaten
> >>
> >>The latter will only return 'true' if we really have entered the BIOS
> >>(platform firmware).
> >Yeah that seems to fit the bill. We already have a check in our suspend
> >paths to figure out whether we'll suspend to idle or go into full S3, so
> >i915 could use them both. And making them generic would make sense I
> >guess.
> OK, sent patches (CCed you), please have a look.

EXPORT_SYMBOL seems missing, but lgtm otherwise. I haven't tried to use
them for the two cases in i915 though.

> Thanks,
> Rafael
> >>>acpi_source_system_state() which usually is S0 and only when acpi
> >>>successfully went into the suspend state in platform_suspend_ops->enter it
> >>>gets set to the value of acpi_target_system_state. And then reset once the
> >>>resume has completed. I think that would be what we'd want here.
> >>We need to new functions like the above, because some things already depend
> >>on acpi_target_system_state working the way it does currently.
> >>
> >>I see no reason to make that ACPI-specific, though, in principle.
> >>
> >>>Anyway I'll pull in Animesh series meanwhile, amended with a FIXME comment.
> >>Fine by me.
> >>
> >>Thanks,
> >>Rafael
> >>
> >>
> >>>>>On Wed, Sep 23, 2015 at 6:28 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> >>>>>>Actually add Rafael this time around ...
> >>>>>>-Daniel
> >>>>>>
> >>>>>>On Wed, Sep 23, 2015 at 6:27 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> >>>>>>>On Wed, Sep 23, 2015 at 9:57 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> >>>>>>>>On Thu, Sep 17, 2015 at 12:53:21AM +0530, Animesh Manna wrote:
> >>>>>>>>>On 9/14/2015 1:16 PM, Daniel Vetter wrote:
> >>>>>>>>>>On Fri, Sep 11, 2015 at 12:36:24AM +0530, Animesh Manna wrote:
> >>>>>>>>>>>On 9/10/2015 8:15 PM, Daniel Vetter wrote:
> >>>>>>>>>>>>On Thu, Sep 10, 2015 at 01:58:54AM +0530, Animesh Manna wrote:
> >>>>>>>>>>>>>On 9/2/2015 2:24 PM, Daniel Vetter wrote:
> >>>>>>>>>>>>>>On Wed, Aug 26, 2015 at 07:40:54PM +0530, Animesh Manna wrote:
> >>>>>>>>>>>>>>>On 8/26/2015 6:40 PM, Daniel Vetter wrote:
> >>>>>>>>>>>>>>>>On Wed, Aug 26, 2015 at 01:36:05AM +0530, Animesh Manna wrote:
> >>>>>>>>>>>>>>>>>Dmc will restore the csr program except DC9, cold boot,
> >>>>>>>>>>>>>>>>>warm reset, PCI function level reset, and hibernate/suspend.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>intel_csr_load_program() function is used to load the firmware
> >>>>>>>>>>>>>>>>>data from kernel memory to csr address space.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>All values of csr address space will be zero if it got reset and
> >>>>>>>>>>>>>>>>>the first byte of csr program is always a non-zero if firmware
> >>>>>>>>>>>>>>>>>is loaded successfuly. Based on hardware status will load the
> >>>>>>>>>>>>>>>>>firmware.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>Without this condition check if we overwrite the firmware data the
> >>>>>>>>>>>>>>>>>counters exposed for dc5/dc6 (help for debugging) will be nullified.
> >>>>>>>>>>>>>>>Bacause of the above reason mentioned just above we need to block firmware loading again.
> >>>>>>>>>>>>>>>So only WARN_ON will not help.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>v1: Initial version.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>v2: Based on review comments from Daniel,
> >>>>>>>>>>>>>>>>>- Added a check to know hardware status and load the firmware if not loaded.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>Cc: Daniel Vetter <daniel.vetter at intel.com>
> >>>>>>>>>>>>>>>>>Cc: Damien Lespiau <damien.lespiau at intel.com>
> >>>>>>>>>>>>>>>>>Cc: Imre Deak <imre.deak at intel.com>
> >>>>>>>>>>>>>>>>>Cc: Sunil Kamath <sunil.kamath at intel.com>
> >>>>>>>>>>>>>>>>>Signed-off-by: Animesh Manna <animesh.manna at intel.com>
> >>>>>>>>>>>>>>>>>Signed-off-by: Vathsala Nagaraju <vathsala.nagaraju at intel.com>
> >>>>>>>>>>>>>>>>>---
> >>>>>>>>>>>>>>>>>  drivers/gpu/drm/i915/intel_csr.c | 9 +++++++++
> >>>>>>>>>>>>>>>>>  1 file changed, 9 insertions(+)
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>diff --git a/drivers/gpu/drm/i915/intel_csr.c b/drivers/gpu/drm/i915/intel_csr.c
> >>>>>>>>>>>>>>>>>index ba1ae03..682cc26 100644
> >>>>>>>>>>>>>>>>>--- a/drivers/gpu/drm/i915/intel_csr.c
> >>>>>>>>>>>>>>>>>+++ b/drivers/gpu/drm/i915/intel_csr.c
> >>>>>>>>>>>>>>>>>@@ -252,6 +252,15 @@ void intel_csr_load_program(struct drm_device *dev)
> >>>>>>>>>>>>>>>>>              return;
> >>>>>>>>>>>>>>>>>      }
> >>>>>>>>>>>>>>>>>+     /*
> >>>>>>>>>>>>>>>>>+      * Dmc will restore the csr the program except DC9, cold boot,
> >>>>>>>>>>>>>>>>>+      * warm reset, PCI function level reset, and hibernate/suspend.
> >>>>>>>>>>>>>>>>>+      * This condition will help to check if csr address space is reset/
> >>>>>>>>>>>>>>>>>+      * not loaded.
> >>>>>>>>>>>>>>>>>+      */
> >>>>>>>>>>>>>>>>Atm we call this from driver load and resume, which doesn seem to cover
> >>>>>>>>>>>>>>>>all the cases you mention in the comment. Should this be a WARN_ON
> >>>>>>>>>>>>>>>>instead? Or do we have troubles in our init sequence where we load too
> >>>>>>>>>>>>>>>>many times?
> >>>>>>>>>>>>>>>Yes, the above statement taken from bspec to describe about the special cases dmc will not restore the firmware.
> >>>>>>>>>>>>>>>Agree, In our cases cold boot and hibernate/suspend mainly we need to load the firmware again, so in my
> >>>>>>>>>>>>>>>second sentence I wanted to comment mainly regarding this condition check added for suspend-hibernate(reset)
> >>>>>>>>>>>>>>>and cold boot(not loaded).
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>Anyways the same api later can be used to load the firmware from anywhere, so my intention to check firmware loaded or not.
> >>>>>>>>>>>>>>>If already loaded then not to overwrite the csr address space to maintain the dc5/dc6 counter value.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>Can the below comment more clear to you.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>        /*
> >>>>>>>>>>>>>>>         * Dmc will restore the csr the program except DC9, cold boot,
> >>>>>>>>>>>>>>>         * warm reset, PCI function level reset, and hibernate/suspend.
> >>>>>>>>>>>>>>>         * If firmware is restored by dmc then no need to load again which
> >>>>>>>>>>>>>>>         * will keep the dc5/dc6 counter exposed by firmware.
> >>>>>>>>>>>>>>>         */
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>No issue in init sequence.
> >>>>>>>>>>>>>>That seems to still cover all the callers of the function afaics - we do
> >>>>>>>>>>>>>>pci resets over suspend resume unconditionally. So I still don't
> >>>>>>>>>>>>>>understand where exactly we try to load the dmc firmware in i915.ko when
> >>>>>>>>>>>>>>it's already loaded.
> >>>>>>>>>>>>>During resume intel_csr_load_program() will be called from
> >>>>>>>>>>>>>intel_runtime_resume().
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>intel_runtime_resume()-> skl_resume_prepare()-> intel_csr_load_program()
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>During Pc10 entry testing I can see dmc is restoring back the firmware always,
> >>>>>>>>>>>>>but as you mentioned pci-reset can happen unconditionally, but still then
> >>>>>>>>>>>>>also during resume intel_runtime_resume() will be called and based on
> >>>>>>>>>>>>>register read of csr-base-address firmware loading will happen.
> >>>>>>>>>>>>But in your comment you're saying it won't get restored in case of dc9 and
> >>>>>>>>>>>>suspend. So that seems to mismatch what you're saying here (and what the
> >>>>>>>>>>>>commit message says) and what the code does. And this function here is
> >>>>>>>>>>>>called for resume after suspend/hibernate only.
> >>>>>>>>>>>pc10 entry explanation I told is for skylake. dc9 in skylake is not possible.
> >>>>>>>>>>>I think you are confusing between dc6 and dc9. Pc10 can be achieved by
> >>>>>>>>>>>entering into dc6 (not dc9) for skylake. dc9 is the lowest possible state
> >>>>>>>>>>>for broxton which is not present for skylake.
> >>>>>>>>>>I have no idea at all about different pc levels on skl. What I'm talking
> >>>>>>>>>>about is system suspend/resume and driver load, which are the places this
> >>>>>>>>>>function gets called. At least afaics.
> >>>>>>>>>>
> >>>>>>>>>>>Here intel_csr_load_program() will be used for both skylake and broxton, and instruction
> >>>>>>>>>>>execution flow will be different in case of suspend/resume which I think is confusing
> >>>>>>>>>>>you.
> >>>>>>>>>>That seems like really important information. What's different on bxt?
> >>>>>>>>>>These are the kind of details you should explain in the commit message ...
> >>>>>>>>>>
> >>>>>>>>>>>I am ready explain you in detail. It will be good if we discuss specific use-case scenario
> >>>>>>>>>>>and itz software design for specific platform. Another point - as dmc related code for
> >>>>>>>>>>>broxton is not merged better first we close design for skylake. Now, I have added dc9
> >>>>>>>>>>>description in comment thinking of future. If you want I can remove for now and later
> >>>>>>>>>>>can add in bxt patch series for enabling dmc. Will wait for your reply.
> >>>>>>>>>>This question here isn't about the overall design and how to handle power
> >>>>>>>>>>wells in skl/bxt. That's a separate discussion and tracked somewhere else.
> >>>>>>>>>>I'm really just confused about when exactly we need to reload to firmware,
> >>>>>>>>>>and why we need a runtime check for that. Normally we should know when to
> >>>>>>>>>>reload the firmware and just either reload or not, without checking hw
> >>>>>>>>>>state. And I don't like checking for hw state since at least in the past
> >>>>>>>>>>that kind of code ended up being fragile - it's an illusion that it does
> >>>>>>>>>>the right thing no matter what, since often there's other tricky ordering
> >>>>>>>>>>constraints. And if you have automatic duct-tape like then no one will
> >>>>>>>>>>ever spot those other, harder to spot issues, until an expensive customer
> >>>>>>>>>>escalation happens.
> >>>>>>>>>>
> >>>>>>>>>>So what I want to know here is:
> >>>>>>>>>>- When exactly do we need to reload dmc firmware.
> >>>>>>>>>In skl, during driver load first time we load the firmware, during normal
> >>>>>>>>>suspend-resume (dc6 entry/exit)
> >>>>>>>>>no need to reload the firmware again as dmc will take care of it. But during
> >>>>>>>>>suspend/hibernation
> >>>>>>>>>dmc will not restore the firmware. In that case driver need to reload it
> >>>>>>>>>again. I do not know
> >>>>>>>>>how to differentiate pm-suspend and suspend-hibernation and thought both the
> >>>>>>>>>cases
> >>>>>>>>>intel_runtime_resume() will be called where we can check the h/w state and
> >>>>>>>>>reload the
> >>>>>>>>>firmware if dmc is not restored.
> >>>>>>>>>
> >>>>>>>>>In bxt, during driver load first time we load the firmware, during normal
> >>>>>>>>>suspend-resume
> >>>>>>>>>display engine will enter into dc9 and dmc will not restore the firmware. So
> >>>>>>>>>every
> >>>>>>>>>suspend-resume we need to reload the firmware.
> >>>>>>>>>>- What exactly is the reason why we can't make that decision statically in
> >>>>>>>>>>   the code (by calling csr_load at the right spots).
> >>>>>>>>>As I mentioned before in case of skylake can we differentiate between
> >>>>>>>>>"resume from pm-suspend" with "resume from suspend-hibernation" inside
> >>>>>>>>>driver?
> >>>>>>>>>
> >>>>>>>>>In case of broxton, every time we need to reload, so we can decide
> >>>>>>>>>statically.
> >>>>>>>>Of course we can differentiate between all the different resume paths, and
> >>>>>>>>we also have a per-platform split to take care of bxt vs. skl. And there
> >>>>>>>>are actually 3 different resume paths:
> >>>>>>>>
> >>>>>>>>- runtime PM resume. This calls the runtime_resume hook. It sounds like on
> >>>>>>>>   skl we should _not_ load the csr firmware, but on bxt we should load it.
> >>>>>>>>   This can be fixed by removing the intel_csr_load_program call from
> >>>>>>>>   skl_resume_prepare.
> >>>>>>>>- resume from hibernate-to-disk (i.e. system completely off, state stored
> >>>>>>>>   on the swap partition) is done by calling the thaw callbacks.
> >>>>>>>>- resume from suspend-to-mem (i.e. system in low-power with only memory
> >>>>>>>>   in self-refresh, all state stored in memory) is done by calling the
> >>>>>>>>   resume callbacks.
> >>>>>>>>
> >>>>>>>>For i915 we use unified handlers in our dev_pm_ops for both thaw and
> >>>>>>>>resume, but it sounds like that won't be a problem for skl/bxt since we
> >>>>>>>>need to reload the csr firmware in all cases. Although I'm not perfectly
> >>>>>>>>sure since you don't explain what kind of resume you mean exactly (since
> >>>>>>>>you don't use the linux names for them).
> >>>>>>>>
> >>>>>>>>Anyway it sounds like we can replace this patch by one where we remove
> >>>>>>>>that errornous csr load call from skl runtime pm resume and that's all.
> >>>>>>>>But I suggest to make sure we get this right we keep the check you're
> >>>>>>>>adding here, but wrap it in a WARN_ON. Then we'll get a backtrace when
> >>>>>>>>this is going wrong again. Like this:
> >>>>>>>>
> >>>>>>>>         if (WARN_ON(csr_loaded_already()))
> >>>>>>>>                 return;
> >>>>>>>>
> >>>>>>>>Also when redoing the commits please explain in detail what exactly are
> >>>>>>>>the requirements like you've done above, but please use the standard linux
> >>>>>>>>names, i.e. "runtime PM" and "hibernate-to-disk" and "suspend-to-mem".
> >>>>>>>Ok hooray there's more suspend-to-something things I've totally missed:
> >>>>>>>- suspend-to-idle (done by cat freeze > /sys/power/state) and
> >>>>>>>- suspend (done by cat suspend > /sys/power/state)
> >>>>>>>
> >>>>>>>And apparently there's really no way to drivers to tell them apart.
> >>>>>>>Rafael, is there really no way for drivers to take different paths for
> >>>>>>>these 3 suspend cases? I tried grepping for PM_SUSPEND_ON/STANDY/MEM
> >>>>>>>and didn't spot anything.
> >>>>>>>
> >>>>>>>Also we're completely missing test coverage for that in igt. That is
> >>>>>>>something that needs to be fixed asap (yet another case of
> >>>>>>>combinatorial explosion in igt tests, yay). And at least one of those
> >>>>>>>suspend-to-idle testcase better be in the BAT.
> >>>>>>>-Daniel
> >>>>>>>--
> >>>>>>>Daniel Vetter
> >>>>>>>Software Engineer, Intel Corporation
> >>>>>>>+41 (0) 79 365 57 48 - http://blog.ffwll.ch
> >>>>>>--
> >>>>>>Daniel Vetter
> >>>>>>Software Engineer, Intel Corporation
> >>>>>>+41 (0) 79 365 57 48 - http://blog.ffwll.ch

Daniel Vetter
Software Engineer, Intel Corporation

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