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

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Message-ID: <CALCETrU9FEoXgWxV+XXwRdKTxUxYj7CD3ropnFb4Pq1cMkucaQ@mail.gmail.com>
Date:	Wed, 15 Apr 2015 16:52:26 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andy Walls <awalls@...metrocast.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, Apr 15, 2015 at 3:50 PM, Andy Walls <awalls@...metrocast.net> wrote:
> 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.

Surely the MPEG-2 decoder/video engine won't overlap the framebuffer,
though.  Am I missing something?

--Andy

>
> 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
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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