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

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 16/06/15 01:27, Luis R. Rodriguez wrote:
> 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.

Ok, sounds fine to me. I'll queue these for 4.2.

 Tomi


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