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

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Date:	Thu, 9 Apr 2015 09:49:58 -0400
From:	Rob Clark <robdclark@...il.com>
To:	Valentin Rothberg <valentinrothberg@...il.com>
Cc:	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 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

BR,
-R

> I found this issue with ./scripts/checkkconfigsymbols.py by diffing yesterday's
> and today's next tree.
>
> Kind regards,
>  Valentin
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