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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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 ...
-Daniel

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
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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