Re: [PATCH v1 09/47] vidoe: fbdev: atyfb: remove and fix MTRR MMIO "hole" work around

On Fri, Mar 27, 2015 at 12:43:55PM -0700, Andy Lutomirski wrote:

On Fri, Mar 27, 2015 at 12:38 PM, Luis R. Rodriguez [off-list ref] wrote:

quoted

On Sat, Mar 21, 2015 at 11:15:14AM +0200, Ville Syrjälä wrote:

quoted

On Fri, Mar 20, 2015 at 04:17:59PM -0700, Luis R. Rodriguez wrote:

quoted

diff --git a/drivers/video/fbdev/aty/atyfb_base.c b/drivers/video/fbdev/aty/atyfb_base.c
index 8025624..8875e56 100644
--- a/drivers/video/fbdev/aty/atyfb_base.c
+++ b/drivers/video/fbdev/aty/atyfb_base.c

@@ -2630,21 +2630,10 @@ static int aty_init(struct fb_info *info)

 #ifdef CONFIG_MTRR
    par->mtrr_aper = -1;
-   par->mtrr_reg = -1;
    if (!nomtrr) {
-           /* Cover the whole resource. */
-           par->mtrr_aper = mtrr_add(par->res_start, par->res_size,
+           par->mtrr_aper = mtrr_add(info->fix.smem_start,
+                                     info->fix.smem_len,
                                      MTRR_TYPE_WRCOMB, 1);

MTRRs need power of two size, so how is this supposed to work?

As per mtrr_add_page() [0] the base and size are just supposed to be in units
of 4 KiB, although the practice is to use powers of 2 in *some* drivers this
is not standardized and by no means recorded as a requirement. Obviously
powers of 2 will work too and you'd end up neatly aligned as well. mtrr_add()
will use mtrr_check() to verify the the same requirement. Furthermore,
as per my commit log message:

Whatever the code may or may not do, the x86 architecture uses
power-of-two MTRR sizes.  So I'm confused.

There should be no confusion, I simply did not know that *was* the
requirement for x86, if that is the case we should add a check for that
and perhaps generalize a helper that does the power of two helper changes,
the cleanest I found was the vesafb driver solution.

Thoughts?

 Luis