Re: [PATCH 1/3] drm/i915: add PCH_NONE to enum intel_pch

From: Daniel Vetter <daniel@ffwll.ch>
To: Paulo Zanoni <przanoni@gmail.com>
Cc: intel-gfx@lists.freedesktop.org, Paulo Zanoni <paulo.r.zanoni@intel.com>
Subject: Re: [PATCH 1/3] drm/i915: add PCH_NONE to enum intel_pch
Date: Wed, 4 Jul 2012 09:49:01 +0200	[thread overview]
Message-ID: <20120704074901.GE5375@phenom.ffwll.local> (raw)
In-Reply-To: <1341352096-19712-1-git-send-email-przanoni@gmail.com>

On Tue, Jul 03, 2012 at 06:48:16PM -0300, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> 
> And rely on the fact that it's 0 to assume that machines without a PCH
> will have PCH_NONE as dev_priv->pch_type.
> 
> Just today I finally realized that HAS_PCH_IBX is true for machines
> without a PCH. IMHO this is totally counter-intuitive and I don't
> think it's a good idea to assume that we're going to check for
> HAS_PCH_IBX only after we check for HAS_PCH_SPLIT.
> 
> I believe that in the future we'll have more PCH types and checks
> like:
> 
>     if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev))
> 
> will become more and more common. There's a good chance that we may
> break non-PCH machines by adding these checks in code that runs on all
> machines. I also believe that the HAS_PCH_SPLIT check will become less
> common as we add more and more different PCH types. We'll probably
> start replacing checks like:
> 
>     if (HAS_PCH_SPLIT(dev))
>         foo();
>     else
>         bar();
> 
> with:
> 
>     if (HAS_PCH_NEW(dev))
>         baz();
>     else if (HAS_PCH_OLD(dev) || HAS_PCH_IBX(dev))
>         foo();
>     else
>         bar();
> 
> and this may break gen 2/3/4.
> 
> As far as we have investigated, this patch will affect the behavior of
> intel_hdmi_dpms and intel_dp_link_down on gen 4. In both functions the
> code inside the HAS_PCH_IBX check is for IBX-specific workarounds, so
> we should be safe. If we start bisecting gen 2/3/4 bugs to this commit
> we should consider replacing the HAS_PCH_IBX checks with something
> else.
> 
> V2: Improve commit message, list possible side effects and solution.
> 
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

All three patches queued for -next, thanks.
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48