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

From: Imre Deak <imre.deak@intel.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org, naresh.kumar.kachhi@intel.com
Subject: Re: [RFC 1/6] drm/i915: cover ioctls with runtime_get/put
Date: Wed, 22 Jan 2014 15:23:28 +0200	[thread overview]
Message-ID: <1390397008.12277.15.camel@intelbox> (raw)
In-Reply-To: <20140122125122.GG9772@phenom.ffwll.local>

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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

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