[Intel-gfx] [PATCH v3] drm/i915: Check HAS_PCH_NOP when install or reset dispaly IRQ

[David Weinehall]

On Thu, Dec 22, 2016 at 10:52:29AM +0200, Jani Nikula wrote:
> On Thu, 22 Dec 2016, "Wang, Elaine" <elaine.wang at intel.com> wrote:
> >> 
> >> On Thu, 22 Dec 2016, "Wang, Elaine" <elaine.wang at intel.com> wrote:
> >> > Hi Jani, Ville,
> >> >
> >> > Any comment about the "PCH_NOP" vs "num_pipes == 0"?
> >> >
> >> > Thanks,
> >> > Elaine
> >> >> On Thu, 15 Dec 2016, Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:
> >> >> > On Mon, Dec 12, 2016 at 02:57:44PM +0800, Wang Elaine wrote:
> >> >> >> From: Elaine Wang <elaine.wang at intel.com>
> >> >> >>
> >> >> >> Some platforms don't have display. To avoid accessing the
> >> >> >> non-existent registers, check HAS_PCH_NOP before invoking display
> >> >> >> IRQ install or reset function.
> >> >> >>
> >> >> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >> >> >> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> >> >> >> Signed-off-by: Elaine Wang <elaine.wang at intel.com>
> >> >> >> ---
> >> >> >>  drivers/gpu/drm/i915/i915_irq.c | 10 +++++++---
> >> >> >>  1 file changed, 7 insertions(+), 3 deletions(-)
> >> >> >>
> >> >> >> diff --git a/drivers/gpu/drm/i915/i915_irq.c
> >> >> >> b/drivers/gpu/drm/i915/i915_irq.c index 0b119b9..369a038 100644
> >> >> >> --- a/drivers/gpu/drm/i915/i915_irq.c
> >> >> >> +++ b/drivers/gpu/drm/i915/i915_irq.c
> >> >> >> @@ -2990,8 +2990,10 @@ static void gen8_irq_reset(struct
> >> >> >> drm_device
> >> >> *dev)
> >> >> >>
> >> >> POWER_DOMAIN_PIPE(pipe)))
> >> >> >>  			GEN8_IRQ_RESET_NDX(DE_PIPE, pipe);
> >> >> >>
> >> >> >> -	GEN5_IRQ_RESET(GEN8_DE_PORT_);
> >> >> >> -	GEN5_IRQ_RESET(GEN8_DE_MISC_);
> >> >> >> +	if (!HAS_PCH_NOP(dev_priv)) {
> >> >> >> +		GEN5_IRQ_RESET(GEN8_DE_PORT_);
> >> >> >> +		GEN5_IRQ_RESET(GEN8_DE_MISC_);
> >> >> >> +	}
> >> >> >
> >> >> > Hmm. These are north side registers so looking at PCH_NOP feels
> >> >> > questionable.
> >> >>
> >> >> Indeed, num_pipes == 0 isn't exactly the same thing as HAS_PCH_NOP.
> >> >>
> >> >> Jani.
> >> >
> >> > I thought HAS_PCH_NOP had same meaning as num_pipes == 0 because I
> >> saw
> >> > following code in i915_drv.c. Is there any exception?
> >> >
> >> > https://cgit.freedesktop.org/drm-intel/tree/drivers/gpu/drm/i915/i915_
> >> > drv.c?h=drm-intel-nightly#n145 static void intel_detect_pch(struct
> >> > drm_i915_private *dev_priv) {
> >> > 	struct pci_dev *pch = NULL;
> >> >
> >> > 	/* In all current cases, num_pipes is equivalent to the PCH_NOP
> >> setting
> >> > 	 * (which really amounts to a PCH but no South Display).
> >> > 	 */
> >> 
> >> The key is in this comment; "In all current cases", where "current" is 3½ years
> >> ago. IIRC this was written for some Xeons which did have a PCH but no
> >> display. PCH_NOP is a kind of hack for those. Nowadays you don't always
> >> have a PCH on gen 5+ (VLV, CHV, BXT, ...). You might have a PCH but only
> >> need the North Display for some outputs. And I guess you might still have a
> >> PCH but no display at all.
> >> 
> >> I'm just saying, we should not overload this hack to, say, cover platforms that
> >> don't even have a PCH, or platforms that have a PCH but a functioning North
> >> Display.
> >> 
> >> BR,
> >> Jani.
> >> 
> > I understand your point now. Thank you for explaining this. I'll update the patch and
> > Use num_pipes for checking whether display engine exists.
> 
> Ville, how about adding something like:
> 
> #define HAS_DISPLAY(dev_priv) (INTEL_INFO(dev_priv)->num_pipes == 0)
> 
> and possibly
> 
> #define HAS_SOUTH_DISPLAY(dev_priv) HAS_PCH_NOP(dev_priv)
> 
> So we could clarify the code, and abstract the rules, so it'll perhaps
> be easier to change them later?
> 
> Though I fear we may end up needing to add a finer granularity depending
> on which parts we do need to and must not touch, and that might not
> always map to low granularity north/south display. *shrug*

Even if we might end up making things more granular later on,
I'm a big fan of self-documenting code. HAS_DISPLAY() clearly
explains what we're testing for, as does HAS_SOUTH_DISPLAY().


Kind regards, David