linux-kernel - Re: [PATCH] [media] ivtv: use arch_phys_wc

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Date:	Mon, 27 Apr 2015 18:43:26 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Andy Walls <awalls@...metrocast.net>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	linux-media@...r.kernel.org, luto@...capital.net, mst@...hat.com,
	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Juergen Gross <jgross@...e.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Antonino Daplas <adaplas@...il.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Arnd Bergmann <arnd@...db.de>,
	Stefan Bader <stefan.bader@...onical.com>,
	Ville Syrjälä <syrjala@....fi>,
	Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
	Borislav Petkov <bp@...e.de>, Davidlohr Bueso <dbueso@...e.de>,
	konrad.wilk@...cle.com, ville.syrjala@...ux.intel.com,
	david.vrabel@...rix.com, jbeulich@...e.com, toshi.kani@...com,
	Roger Pau Monné <roger.pau@...rix.com>,
	ivtv-devel@...vdriver.org, xen-devel@...ts.xensource.com
Subject: Re: [PATCH] [media] ivtv: use arch_phys_wc_add() and require PAT
 disabled

On Sat, Apr 25, 2015 at 07:12:05AM -0400, Andy Walls wrote:
> Hi Luis,
> 
> Sorry for the late reply.
> 
> Thank you for the patch! See my comments below:
> 
> On Wed, 2015-04-22 at 12:33 -0700, Luis R. Rodriguez wrote:
> > From: "Luis R. Rodriguez" <mcgrof@...e.com>
> > 
> > We are burrying direct access to MTRR code support on
> > x86 in order to take advantage of PAT. In the future we
> > also want to make the default behaviour of ioremap_nocache()
> > to use strong UC, use of mtrr_add() on those systems
> > would make write-combining void.
> > 
> > In order to help both enable us to later make strong
> > UC default and in order to phase out direct MTRR access
> > code port the driver over to arch_phys_wc_add() and
> > annotate that the device driver requires systems to
> > boot with PAT disabled, with the nopat kernel parameter.
> > 
> > This is a worthy comprmise given that the hardware is
> > really rare these days,
> 
> I'm OK with the compromise solution.  It makes sense.

OK great!

> > diff --git a/drivers/media/pci/ivtv/ivtvfb.c b/drivers/media/pci/ivtv/ivtvfb.c
> > index 9ff1230..552408b 100644
> > --- a/drivers/media/pci/ivtv/ivtvfb.c
> > +++ b/drivers/media/pci/ivtv/ivtvfb.c
> > @@ -1120,6 +1121,7 @@ static int ivtvfb_init_io(struct ivtv *itv)
> >  	oi->video_buffer_size = 1704960;
> >  
> >  	oi->video_pbase = itv->base_addr + IVTV_DECODER_OFFSET + oi->video_rbase;
> > +	/* XXX: split this for PAT */
> 
> Please remove this comment. 

Done.

> > @@ -1190,6 +1172,13 @@ static int ivtvfb_init_card(struct ivtv *itv)
> >  {
> >  	int rc;
> >  
> > +#ifdef CONFIG_X86_64
> > +	if (WARN(pat_enabled,
> 
> This check might be better placed in ivtvfb_init().  This check is going
> to have the same result for every PVR-350 card in the system that is
> found by ivtvfb.

OK moved!

> > +		 "ivtv needs PAT disabled, boot with nopat kernel parameter\n")) {
> 
> This needs to read "ivtvfb needs [...]" to avoid user confusion with the
> main ivtv driver module.

OK!

> This change is the only one I really care about.  Then I can give my
> Ack.

OK!

  Luis
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