Re: [PATCH v4 3/3] video: fbdev: vesafb: use arch_phys_wc_add()

["Luis R. Rodriguez" <mcgrof@suse.com>]

On Fri, Jun 12, 2015 at 12:04:14PM +0300, Tomi Valkeinen wrote:
> 
> 
> On 04/06/15 19:44, Luis R. Rodriguez wrote:
> > From: "Luis R. Rodriguez" <mcgrof@suse.com>
> > 
> > This driver uses the same area for MTRR as for the ioremap_wc(), if
> > anything it just uses a smaller size in case MTRR reservation fails.
> > ioremap_wc() API is already used to take advantage of architecture
> > write-combining when available.
> > 
> > Convert the driver from using the x86 specific MTRR code to
> > the architecture agnostic arch_phys_wc_add(). arch_phys_wc_add()
> > will avoid MTRR if write-combining is available.
> > 
> > There are a few motivations for this:
> > 
> > a) Take advantage of PAT when available
> > 
> > b) Help bury MTRR code away, MTRR is architecture specific and on
> >    x86 its replaced by PAT
> > 
> > c) Help with the goal of eventually using _PAGE_CACHE_UC over
> >    _PAGE_CACHE_UC_MINUS on x86 on ioremap_nocache() (see commit
> >    de33c442e titled "x86 PAT: fix performance drop for glx,
> >    use UC minus for ioremap(), ioremap_nocache() and
> >    pci_mmap_page_range()")
> > 
> > The conversion done is expressed by the following Coccinelle
> > SmPL patch, it additionally required manual intervention to
> > address all the #ifdery and removal of redundant things which
> > arch_phys_wc_add() already addresses such as verbose message
> > about when MTRR fails and doing nothing when we didn't get
> > an MTRR.
> > 
> > @ mtrr_found @
> > expression index, base, size;
> > @@
> > 
> > -index = mtrr_add(base, size, MTRR_TYPE_WRCOMB, 1);
> > +index = arch_phys_wc_add(base, size);
> > 
> > @ mtrr_rm depends on mtrr_found @
> > expression mtrr_found.index, mtrr_found.base, mtrr_found.size;
> > @@
> > 
> > -mtrr_del(index, base, size);
> > +arch_phys_wc_del(index);
> > 
> > @ mtrr_rm_zero_arg depends on mtrr_found @
> > expression mtrr_found.index;
> > @@
> > 
> > -mtrr_del(index, 0, 0);
> > +arch_phys_wc_del(index);
> > 
> > @ mtrr_rm_fb_info depends on mtrr_found @
> > struct fb_info *info;
> > expression mtrr_found.index;
> > @@
> > 
> > -mtrr_del(index, info->fix.smem_start, info->fix.smem_len);
> > +arch_phys_wc_del(index);
> > 
> > @ ioremap_replace_nocache depends on mtrr_found @
> > struct fb_info *info;
> > expression base, size;
> > @@
> > 
> > -info->screen_base = ioremap_nocache(base, size);
> > +info->screen_base = ioremap_wc(base, size);
> > 
> > @ ioremap_replace_default depends on mtrr_found @
> > struct fb_info *info;
> > expression base, size;
> > @@
> > 
> > -info->screen_base = ioremap(base, size);
> > +info->screen_base = ioremap_wc(base, size);
> > 
> > Generated-by: Coccinelle SmPL
> > Cc: Toshi Kani <toshi.kani@hp.com>
> > Cc: Suresh Siddha <sbsiddha@gmail.com>
> > Cc: Ingo Molnar <mingo@elte.hu>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Juergen Gross <jgross@suse.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: Andy Lutomirski <luto@amacapital.net>
> > Cc: Dave Airlie <airlied@redhat.com>
> > Cc: Antonino Daplas <adaplas@gmail.com>
> > Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
> > Cc: Rob Clark <robdclark@gmail.com>
> > Cc: Jingoo Han <jg1.han@samsung.com>
> > Cc: Wolfram Sang <wsa@the-dreams.de>
> > Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> > Cc: linux-fbdev@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
> > ---
> >  drivers/video/fbdev/vesafb.c | 29 ++++++++---------------------
> >  1 file changed, 8 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c
> > index 3db3908..528fe91 100644
> > --- a/drivers/video/fbdev/vesafb.c
> > +++ b/drivers/video/fbdev/vesafb.c
> > @@ -19,10 +19,9 @@
> >  #include <linux/init.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/screen_info.h>
> > +#include <linux/io.h>
> >  
> >  #include <video/vga.h>
> > -#include <asm/io.h>
> > -#include <asm/mtrr.h>
> >  
> >  #define dac_reg	(0x3c8)
> >  #define dac_val	(0x3c9)
> > @@ -180,16 +179,10 @@ static int vesafb_setcolreg(unsigned regno, unsigned red, unsigned green,
> >  
> >  static void vesafb_destroy(struct fb_info *info)
> >  {
> > -#ifdef CONFIG_MTRR
> >  	struct vesafb_par *par = info->par;
> > -#endif
> >  
> >  	fb_dealloc_cmap(&info->cmap);
> > -
> > -#ifdef CONFIG_MTRR
> > -	if (par->wc_cookie >= 0)
> > -		mtrr_del(par->wc_cookie, 0, 0);
> > -#endif
> > +	arch_phys_wc_del(par->wc_cookie);
> >  	if (info->screen_base)
> >  		iounmap(info->screen_base);
> >  	release_mem_region(info->apertures->ranges[0].base, info->apertures->ranges[0].size);
> > @@ -420,7 +413,6 @@ static int vesafb_probe(struct platform_device *dev)
> >  	request_region(0x3c0, 32, "vesafb");
> >  
> >  	if (mtrr = 3) {
> > -#ifdef CONFIG_MTRR
> >  		unsigned int temp_size = size_total;
> >  
> >  		/* Find the largest power-of-two */
> > @@ -428,18 +420,16 @@ static int vesafb_probe(struct platform_device *dev)
> >  
> >  		/* Try and find a power of two to add */
> >  		do {
> > -			par->wc_cookie = mtrr_add(vesafb_fix.smem_start,
> > -						  temp_size,
> > -						  MTRR_TYPE_WRCOMB, 1);
> > +			par->wc_cookie > > +				arch_phys_wc_add(vesafb_fix.smem_start,
> > +						 temp_size);
> >  			temp_size >>= 1;
> > -		} while (temp_size >= PAGE_SIZE && par->wc_cookie = -EINVAL);
> > -#endif
> > +		} while (temp_size >= PAGE_SIZE && par->wc_cookie < 0);
> > +
> 
> Looks like arch_phys_wc_add prints a warning if it fails, and the above
> loop may retry it many (?) times. Probably not a big issue, but may be
> somewhat confusing.

On most systems arch_phys_wc_add() won't ever run so I think that's a
fair compromise to reach as we phase out MTRR. If we really wanted
to fix this one could generalize the whole loop control stuff and use
a new arch_phys API to generalize all that code as tons of drivers
borrow the same logic. I decided this was pointless as we're phasing
this out anyway and this code will simply be a no-op on most systems
now.

Let me know if you have any other preference or ideas.

  Luis