linux-kernel - Re: [Xen-devel] [PATCH v1 04/47] pci: add pci_ioremap_wc

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Date:	Wed, 25 Mar 2015 21:39:14 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>, luto@...capital.net,
	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
	jgross@...e.com, JBeulich@...e.com, bp@...e.de,
	suresh.b.siddha@...el.com, venkatesh.pallipadi@...el.com,
	airlied@...hat.com, linux-fbdev@...r.kernel.org,
	Antonino Daplas <adaplas@...il.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	xen-devel@...ts.xenproject.org, Ingo Molnar <mingo@...e.hu>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>
Subject: Re: [Xen-devel] [PATCH v1 04/47] pci: add pci_ioremap_wc_bar()

On Wed, Mar 25, 2015 at 04:03:46PM -0400, Konrad Rzeszutek Wilk wrote:
> On Fri, Mar 20, 2015 at 04:17:54PM -0700, Luis R. Rodriguez wrote:
> > From: "Luis R. Rodriguez" <mcgrof@...e.com>
> > 
> > This lets drivers take advanate of PAT when available. This
> 
> s/advanate/advantage/

Amended.

> > should help with the transition of converting video drivers over
> > to ioremap_wc() to help with the goal of eventually using
> > _PAGE_CACHE_UC over _PAGE_CACHE_UC_MINUS on x86 on
> > ioremap_nocache() (de33c442e)
> 
> Please mention the title of the patch too:
> 
> "x86 PAT: fix performance drop for glx, use UC minus for ioremap(), ioremap_nocache() and pci_mmap_page_range()"

Added.

> > 
> > Cc: Suresh Siddha <suresh.b.siddha@...el.com>
> > Cc: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
> > Cc: Ingo Molnar <mingo@...e.hu>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Juergen Gross <jgross@...e.com>
> > Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> > Cc: Andy Lutomirski <luto@...capital.net>
> > Cc: Dave Airlie <airlied@...hat.com>
> > Cc: Antonino Daplas <adaplas@...il.com>
> > Cc: Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>
> > Cc: Tomi Valkeinen <tomi.valkeinen@...com>
> > Cc: linux-fbdev@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Luis R. Rodriguez <mcgrof@...e.com>
> > ---
> >  drivers/pci/pci.c   | 14 ++++++++++++++
> >  include/linux/pci.h |  1 +
> >  2 files changed, 15 insertions(+)
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 81f06e8..6afd507 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -137,6 +137,20 @@ void __iomem *pci_ioremap_bar(struct pci_dev *pdev, int bar)
> >  				     pci_resource_len(pdev, bar));
> >  }
> >  EXPORT_SYMBOL_GPL(pci_ioremap_bar);
> > +
> > +void __iomem *pci_ioremap_wc_bar(struct pci_dev *pdev, int bar)
> > +{
> > +	/*
> > +	 * Make sure the BAR is actually a memory resource, not an IO resource
> > +	 */
> > +	if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM)) {
> > +		WARN_ON(1);
> 
> Would it be better to use dev_warn ? That way you can see which BDF it is?
> 
> Thought WARN will give a nice stack-trace that should easily point to the
> driver so perhaps not.. Either way - up to you.

I'm sticking to the style and use as with pci_ioremap_bar(). Whatever we pick
we should make both use the same. More information is always better and
since we do have dev_warn(), it would be nice to use that however within
its use on both pci_ioremap_wc_bar() and pci_ioremap_bar() we have
a use of the pdev with pci_resource_flags() and I believe if pdev is NULL
we'd get a NULL dereference (dev_driver_string() is used), so it would
seem it might be best to stick with a simple WARN_ON(). Arjan, any
preference? Obviously if pdev is NULL your driver is dumb but as folks
develop drivers this should be expected.

 Luis
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