[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v1 09/47] vidoe: fbdev: atyfb: remove and fix MTRR MMIO "hole" work around
On Fri, Mar 27, 2015 at 12:38 PM, Luis R. Rodriguez <mcgrof@xxxxxxxx> wrote: > On Sat, Mar 21, 2015 at 11:15:14AM +0200, Ville SyrjÃlà wrote: >> On Fri, Mar 20, 2015 at 04:17:59PM -0700, Luis R. Rodriguez wrote: >> > 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. --Andy > > --- > The last thing we do must do to remain sane is ensure we > use the info->fix.smem_start and info->fix.smem_len for > the framebuffer MTRR as we know that is always well adjusted. > The *one* concern here would be if the MTRR is not in units > of 4K __but__ we already know that in the PCI case this cannot > happen, in the shared space setting the MTRR would be up to > 0x7ff000 and assuming a 4K page: > > ; 0x7ff000 / 0x1000 > 2047 > > Also, internally when MTRR is used mtrr_add() will use mtrr_check() > and that should splat a warning when the MTRR base and size are > not compatible with what is expected for MTRR usage. > --- > > If any of this is too risky we can use the __arch_phys_wc_add() (or as > Andy suggested perhaps use set_page_* stuff, although I am still evaluating > this) but I did this change to show the effort required for a change when > the registers / framebuffer is on the same PCI BAR but at different offsets. > > [0] scripts/kernel-doc -man -function mtrr_add_page > arch/x86/kernel/cpu/mtrr/main.c | nroff -man | less > > Luis -- Andy Lutomirski AMA Capital Management, LLC _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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