[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 23 09:28:43 PDT 2015
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
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