linux-kernel - Re: ioremap_uc() followed by set_memory_wc()

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Date:	Wed, 15 Apr 2015 18:50:12 -0400
From:	Andy Walls <awalls@...metrocast.net>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"Luis R. Rodriguez" <mcgrof@...e.com>, linux-rdma@...r.kernel.org,
	Toshi Kani <toshi.kani@...com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Sean Hefty <sean.hefty@...el.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	Mike Marciniszyn <mike.marciniszyn@...el.com>,
	Roland Dreier <roland@...estorage.com>,
	Juergen Gross <jgross@...e.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Borislav Petkov <bp@...e.de>, Mel Gorman <mgorman@...e.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Davidlohr Bueso <dbueso@...e.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ville Syrjälä <syrjala@....fi>,
	Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
	linux-media@...r.kernel.org, X86 ML <x86@...nel.org>
Subject: Re: ioremap_uc() followed by set_memory_wc() - burrying MTRR

On Wed, 2015-04-15 at 13:42 -0700, Andy Lutomirski wrote:
> On Mon, Apr 13, 2015 at 10:49 AM, Luis R. Rodriguez <mcgrof@...e.com> wrote:
> 
> > c) ivtv: the driver does not have the PCI space mapped out separately, and
> > in fact it actually does not do the math for the framebuffer, instead it lets
> > the device's own CPU do that and assume where its at, see
> > ivtvfb_get_framebuffer() and CX2341X_OSD_GET_FRAMEBUFFER, it has a get
> > but not a setter. Its not clear if the firmware would make a split easy.
> > We'd need ioremap_ucminus() here too and __arch_phys_wc_add().
> >
> 
> IMO this should be conceptually easy to split.  Once we get the
> framebuffer address, just unmap it (or don't prematurely map it) and
> then ioremap the thing.

Not so easy.  The main ivtv driver has already set up the PCI device and
done the mapping for the MPEG-2 decoder/video output engine.  The video
decoder/output device nodes might already be open by user space calling
into the main driver, before the ivtvfb module is even loaded.

This could be mitigated by integrating all the ivtvfb module code into
the main ivtv module.  But even then not every PVR-350 owner wants to
use the video output OSD as a framebuffer.  Users might just want an
actual OSD overlaying their TV video playback.

Regards,
Andy

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