Re: [PATCH v2] ivtv: use arch_phys_wc_add() and require PAT disabled

[Andy Walls <andy@silverblocksystems.net>]

On Mon, 2015-04-27 at 09:43 -0700, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <mcgrof@suse.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, and perhaps only some lost souls
> in some third world country are expected to be using this
> feature of the device driver.
> 
> Cc: Andy Walls <awalls@md.metrocast.net>

Acked-by: Andy Walls <awalls@md.metrocast.net>

Regards,
Andy

> Cc: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
> Cc: Andy Lutomirski <luto@amacapital.net>
> 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: Dave Airlie <airlied@redhat.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Antonino Daplas <adaplas@gmail.com>
> Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Stefan Bader <stefan.bader@canonical.com>
> Cc: Ville Syrjälä <syrjala@sci.fi>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Davidlohr Bueso <dbueso@suse.de>
> Cc: konrad.wilk@oracle.com
> Cc: ville.syrjala@linux.intel.com
> Cc: david.vrabel@citrix.com
> Cc: jbeulich@suse.com
> Cc: toshi.kani@hp.com
> Cc: Roger Pau Monné <roger.pau@citrix.com>
> Cc: linux-fbdev@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: ivtv-devel@ivtvdriver.org
> Cc: linux-media@vger.kernel.org
> Cc: xen-devel@lists.xensource.com
> Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
> ---
> 
> This v2 moves the PAT bail out error check on to ivtvfb_init()
> as per Andy's request. It also removes some comment about TODO
> items for PAT.
> 
>  drivers/media/pci/ivtv/Kconfig  |  3 +++
>  drivers/media/pci/ivtv/ivtvfb.c | 58 ++++++++++++++++-------------------------
>  2 files changed, 26 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/media/pci/ivtv/Kconfig b/drivers/media/pci/ivtv/Kconfig
> index dd6ee57e..b2a7f88 100644
> --- a/drivers/media/pci/ivtv/Kconfig
> +++ b/drivers/media/pci/ivtv/Kconfig
> @@ -57,5 +57,8 @@ config VIDEO_FB_IVTV
>  	  This is used in the Hauppauge PVR-350 card. There is a driver
>  	  homepage at <http://www.ivtvdriver.org>.
>  
> +	  If you have this hardware you will need to boot with PAT disabled
> +	  on your x86 systems, use the nopat kernel parameter.
> +
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called ivtvfb.
> diff --git a/drivers/media/pci/ivtv/ivtvfb.c b/drivers/media/pci/ivtv/ivtvfb.c
> index 9ff1230..8761e3e 100644
> --- a/drivers/media/pci/ivtv/ivtvfb.c
> +++ b/drivers/media/pci/ivtv/ivtvfb.c
> @@ -44,8 +44,8 @@
>  #include <linux/ivtvfb.h>
>  #include <linux/slab.h>
>  
> -#ifdef CONFIG_MTRR
> -#include <asm/mtrr.h>
> +#ifdef CONFIG_X86_64
> +#include <asm/pat.h>
>  #endif
>  
>  #include "ivtv-driver.h"
> @@ -155,12 +155,11 @@ struct osd_info {
>  	/* Buffer size */
>  	u32 video_buffer_size;
>  
> -#ifdef CONFIG_MTRR
>  	/* video_base rounded down as required by hardware MTRRs */
>  	unsigned long fb_start_aligned_physaddr;
>  	/* video_base rounded up as required by hardware MTRRs */
>  	unsigned long fb_end_aligned_physaddr;
> -#endif
> +	int wc_cookie;
>  
>  	/* Store the buffer offset */
>  	int set_osd_coords_x;
> @@ -1099,6 +1098,8 @@ static int ivtvfb_init_vidmode(struct ivtv *itv)
>  static int ivtvfb_init_io(struct ivtv *itv)
>  {
>  	struct osd_info *oi = itv->osd_info;
> +	/* Find the largest power of two that maps the whole buffer */
> +	int size_shift = 31;
>  
>  	mutex_lock(&itv->serialize_lock);
>  	if (ivtv_init_on_first_open(itv)) {
> @@ -1132,29 +1133,16 @@ static int ivtvfb_init_io(struct ivtv *itv)
>  			oi->video_pbase, oi->video_vbase,
>  			oi->video_buffer_size / 1024);
>  
> -#ifdef CONFIG_MTRR
> -	{
> -		/* Find the largest power of two that maps the whole buffer */
> -		int size_shift = 31;
> -
> -		while (!(oi->video_buffer_size & (1 << size_shift))) {
> -			size_shift--;
> -		}
> -		size_shift++;
> -		oi->fb_start_aligned_physaddr = oi->video_pbase & ~((1 << size_shift) - 1);
> -		oi->fb_end_aligned_physaddr = oi->video_pbase + oi->video_buffer_size;
> -		oi->fb_end_aligned_physaddr += (1 << size_shift) - 1;
> -		oi->fb_end_aligned_physaddr &= ~((1 << size_shift) - 1);
> -		if (mtrr_add(oi->fb_start_aligned_physaddr,
> -			oi->fb_end_aligned_physaddr - oi->fb_start_aligned_physaddr,
> -			     MTRR_TYPE_WRCOMB, 1) < 0) {
> -			IVTVFB_INFO("disabled mttr\n");
> -			oi->fb_start_aligned_physaddr = 0;
> -			oi->fb_end_aligned_physaddr = 0;
> -		}
> -	}
> -#endif
> -
> +	while (!(oi->video_buffer_size & (1 << size_shift)))
> +		size_shift--;
> +	size_shift++;
> +	oi->fb_start_aligned_physaddr = oi->video_pbase & ~((1 << size_shift) - 1);
> +	oi->fb_end_aligned_physaddr = oi->video_pbase + oi->video_buffer_size;
> +	oi->fb_end_aligned_physaddr += (1 << size_shift) - 1;
> +	oi->fb_end_aligned_physaddr &= ~((1 << size_shift) - 1);
> +	oi->wc_cookie = arch_phys_wc_add(oi->fb_start_aligned_physaddr,
> +					 oi->fb_end_aligned_physaddr -
> +					 oi->fb_start_aligned_physaddr);
>  	/* Blank the entire osd. */
>  	memset_io(oi->video_vbase, 0, oi->video_buffer_size);
>  
> @@ -1172,14 +1160,7 @@ static void ivtvfb_release_buffers (struct ivtv *itv)
>  
>  	/* Release pseudo palette */
>  	kfree(oi->ivtvfb_info.pseudo_palette);
> -
> -#ifdef CONFIG_MTRR
> -	if (oi->fb_end_aligned_physaddr) {
> -		mtrr_del(-1, oi->fb_start_aligned_physaddr,
> -			oi->fb_end_aligned_physaddr - oi->fb_start_aligned_physaddr);
> -	}
> -#endif
> -
> +	arch_phys_wc_del(oi->wc_cookie);
>  	kfree(oi);
>  	itv->osd_info = NULL;
>  }
> @@ -1284,6 +1265,13 @@ static int __init ivtvfb_init(void)
>  	int registered = 0;
>  	int err;
>  
> +#ifdef CONFIG_X86_64
> +	if (WARN(pat_enabled,
> +		 "ivtvfb needs PAT disabled, boot with nopat kernel parameter\n")) {
> +		return EINVAL;
> +	}
> +#endif
> +
>  	if (ivtvfb_card_id < -1 || ivtvfb_card_id >= IVTV_MAX_CARDS) {
>  		printk(KERN_ERR "ivtvfb:  ivtvfb_card_id parameter is out of range (valid range: -1 - %d)\n",
>  		     IVTV_MAX_CARDS - 1);