linux-kernel - Re: [PATCH 1/2] drm/msm: Register irq handler for each sub-system in mdss

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Date:	Thu, 20 Nov 2014 09:57:52 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Rob Clark <robdclark@...il.com>
Cc:	Hai Li <hali@...eaurora.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 1/2] drm/msm: Register irq handler for each sub-system in
 mdss

On Sun, Nov 16, 2014 at 09:18:47AM -0500, Rob Clark wrote:
> On Fri, Nov 14, 2014 at 5:42 PM, Hai Li <hali@...eaurora.org> wrote:
> > All the sub-systems in mdss share the same irq. This change provides
> > the sub-systems with the interfaces to register/unregister their own
> > irq handlers.
> >
> > With this change, struct mdp5_kms does not have to keep the hdmi or
> > edp context.
> >
> 
> So, I think the point of this is to better deal w/ different hw
> variants which do or do-not have hdmi, edp, dsi, etc..
> 
> But, just playing devil's advocate here, it seems like it would be
> simpler to instead just do something like:
> 
>     if (priv->hdmi && (intr & MDP5_HW_INTR_STATUS_INTR_HDMI))
>         hdmi_irq(0, priv->hdmi);
> 
>     if (priv->edp && (intr & MDP5_HW_INTR_STATUS_INTR_EDP))
>         edp_irq(0, priv->edp);
> 
>     ... etc ...
> 
> It is a little less elegant.  But it is also less lines of code.  I
> guess there will be plenty of necessary complexity as we add support
> for all mdp5 features.  So avoiding some unnecessary complexity might
> be a good thing in the long run.
> 
> If we really did want to make it more dynamic, we could always extend
> 'struct mdp_irq' to take both an irq mask and an initiator id, I
> suppose.  I'm not sure if that is overkill.  AFAICT we really only
> have 5 different subsystems to dispatch to (mdp5 itself, and
> dsi0/dsi1/hdmi/edp), so simply adding some if-not-null checks in
> mdp5_irq() seems pretty reasonable to me.

To me this just seems like a regular interrupt multiplexer, so
implementing it as an irq_chip would be the most appropriate. That way
you get all the goodness of a well-tested code base for free and you can
simply pass in the request_{threaded_,}irq()'s dev parameter.

Thierry

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