linux-kernel - Re: drm/msm/mdp5: undefined CONFIG_MSM_BUS

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Date:	Thu, 9 Apr 2015 16:20:24 +0200
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Rob Clark <robdclark@...il.com>
Cc:	Valentin Rothberg <valentinrothberg@...il.com>,
	Hai Li <hali@...eaurora.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Airlie <airlied@...ux.ie>,
	Paul Bolle <pebolle@...cali.nl>, rupran@...server.de,
	stefan.hengelein@....de
Subject: Re: drm/msm/mdp5: undefined CONFIG_MSM_BUS_SCALING

On Thu, Apr 09, 2015 at 09:49:58AM -0400, Rob Clark wrote:
> On Thu, Apr 9, 2015 at 7:22 AM, Valentin Rothberg
> <valentinrothberg@...il.com> wrote:
> > Hi Hai,
> >
> > your commit d5af49c92a8a ("drm/msm/mdp5: Enable DSI connector in msm drm
> > driver") in today's Linux next tree adds an #ifdef with CONFIG_MSM_BUS_SCALING
> > as condition.  MSM_BUS_SCALING is not defined in Kconfig, so the code in this
> > #ifdef block won't be compiled at its current state.
> >
> > I saw some references on this Kconfig option in other files; is there a
> > reason for the absence of MSM_BUS_SCALING?
> 
> right now, it is something that only exists in downstream kernels (for
> example, android device kernels).. but in those kernels it is
> mandatory to use, as by default the memory/bus is downclocked and the
> display would underflow if we did not request sufficient bandwidth.
> 
> It only exists right now in the upstream kernel to simplify
> backporting to various device kernels

That's crazy.  You are asking upstream to maintain code in order to just
make out of tree crap easier to maintain, which you don't have any plan
to ever upstream?  That causes havoc on static analysis tools and
prevents anyone from ever being able to even change the code for new api
changes and test build it.

If this was in a subsystem that I maintain, I'd delete it tomorrow.  But
in the end, it's up to David to decide if he wants to waste the cycles
or not.

Ick ick ick.

greg k-h
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