Re: [RFC 1/6] drm/i915: cover ioctls with runtime_get/put

[Naresh Kumar Kachhi <naresh.kumar.kachhi@intel.com>]

On 02/22/2014 01:37 AM, Jesse Barnes wrote:
> On Fri, 24 Jan 2014 19:23:54 +0200
> Imre Deak <imre.deak@intel.com> wrote:
>
>> On Fri, 2014-01-24 at 20:35 +0530, Naresh Kumar Kachhi wrote:
>>> On 01/22/2014 06:53 PM, Imre Deak wrote:
>>>
>>>> On Wed, 2014-01-22 at 13:51 +0100, Daniel Vetter wrote:
>>>>> On Wed, Jan 22, 2014 at 05:34:17PM +0530, naresh.kumar.kachhi@intel.com wrote:
>>>>>> From: Naresh Kumar Kachhi <naresh.kumar.kachhi@intel.com>
>>>>>>
>>>>>> With runtime PM enabled, we need to make sure that all HW access
>>>>>> are valid (i.e.  Gfx is in D0). Invalid accesses might end up in
>>>>>> HW hangs. Ex. A hang is seen if display register is accessed on
>>>>>> BYT while display power island is power gated.
>>>>>>
>>>>>> This patch is covering all the IOCTLs with get/put.
>>>>>> TODO: limit runtime_get/put to IOCTLs that accesses HW
>>>>>>
>>>>>> Signed-off-by: Naresh Kumar Kachhi <naresh.kumar.kachhi@intel.com>
>>>>> Nack on the concept. We need to have get/put calls for the individual
>>>>> functional blocks of the hw, which then in turn (if it's not the top-level
>>>>> power domain) need to grab references to the next up power domain.
>>>>> Splattering unconditional get/puts over all driver entry points is bad
>>>>> style and imo also too fragile.
>>>>>
>>>>> Also, with Paulos final runtime pm/pc8 unification patches and Imre's
>>>>> display power well patches for byt we should have full coverage already.
>>>>> Have you looked at the work of these too?
>>>> I'm still in debt with the BYT specific power domain patches, I want to
>>>> post them (this week) after I sorted out spurious pipe stat IRQs we'd
>>>> receive atm with the power well off. Until then there is only the WIP
>>>> version at: https://github.com/ideak/linux/commits/powerwells
>>>>
>>>> But in practice, as you point out the plan was to only call
>>>> modeset_update_power_wells() during modeset time and that will end up
>>>> doing the proper RPM get/put as necessary. Similarly on some other code
>>>> paths like connector detect and HW state read-out code, we'd ask only
>>>> for the needed power domains which would end up doing the RPM get/put.
>>>>
>>>> --Imre
>>>>
>>> Hi Imre,
>>> I tried to go through your and Paulo's patches (http://patchwork.freedesktop.org/patch/16952/).
>>> As per my understanding we are doing disp power well gate/ungate independent of we are in
>>> runtime_suspend/resume state we might face problem here as on BYT interrupts are routed through
>>> display power well, so we might have a situation where display power island is power gated,
>>> but render workload is still active. As we won't be receiving any interrupt __wait_seq_no will
>>> stall and we might end up in a TDR. We will not see the issue until display power gating is
>>> enabled. I will try to include a test to cover this test
>> Hm, which exact interrupt routing are you referring to? At least on my
>> BYT I manage to power off only the display power well and keep the
>> render well on, while still being able to run for example
>> igt/tests/gem_render_copy, gem_render_linear_blits. I can see that
>> through /proc/interrupts that GT interrupts are properly generated. The
>> display side interrupt routing is of course off, for example the
>> PIPESTAT registers will read all 0xffffffff, but DEIIR, DEIMR, DEISR are
>> all seem to work ok.
> I think Naresh is referring to full D3 state shutdown, where the Gunit
> goes away too.  But in that case the GT will be shut down as well, so I
> don't think the display vs GT thing by itself is a problem.
>
Please ignore my previous comment as I confused interrupts being routed through display unit on VLV.
But this comment will be valid on some platforms like HSW, where render interrupts are routed
through display unit. So, display power gating in such platforms has to be done by taking
render/media also into consideration.
-Naresh