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

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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

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.

Anyway I'll pull in Animesh series meanwhile, amended with a FIXME
comment.
-Daniel

> 
> Thanks,
> Rafael
> 
> 
> >On Wed, Sep 23, 2015 at 6:28 PM, Daniel Vetter <daniel@xxxxxxxx> wrote:
> >>Actually add Rafael this time around ...
> >>-Daniel
> >>
> >>On Wed, Sep 23, 2015 at 6:27 PM, Daniel Vetter <daniel@xxxxxxxx> wrote:
> >>>On Wed, Sep 23, 2015 at 9:57 AM, Daniel Vetter <daniel@xxxxxxxx> 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@xxxxxxxxx>
> >>>>>>>>>>>>>Cc: Damien Lespiau <damien.lespiau@xxxxxxxxx>
> >>>>>>>>>>>>>Cc: Imre Deak <imre.deak@xxxxxxxxx>
> >>>>>>>>>>>>>Cc: Sunil Kamath <sunil.kamath@xxxxxxxxx>
> >>>>>>>>>>>>>Signed-off-by: Animesh Manna <animesh.manna@xxxxxxxxx>
> >>>>>>>>>>>>>Signed-off-by: Vathsala Nagaraju <vathsala.nagaraju@xxxxxxxxx>
> >>>>>>>>>>>>>---
> >>>>>>>>>>>>>  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
http://blog.ffwll.ch
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