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

[Tomi Valkeinen]

On 04/06/15 19:44, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
> 
> 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@xxxxxx>
> Cc: Suresh Siddha <sbsiddha@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxxxx>
> Cc: Antonino Daplas <adaplas@xxxxxxxxx>
> Cc: Jean-Christophe Plagniol-Villard <plagnioj@xxxxxxxxxxxx>
> Cc: Rob Clark <robdclark@xxxxxxxxx>
> Cc: Jingoo Han <jg1.han@xxxxxxxxxxx>
> Cc: Wolfram Sang <wsa@xxxxxxxxxxxxx>
> Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> Cc: linux-fbdev@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx>
> ---
>  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.

 Tomi

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