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

Andy Lutomirski
2015-03-27T21:22:00Z

On Fri, Mar 27, 2015 at 1:12 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> On Fri, Mar 20, 2015 at 04:52:18PM -0700, Andy Lutomirski wrote:
>> On Fri, Mar 20, 2015 at 4:17 PM, Luis R. Rodriguez
>> <mcgrof@do-not-panic.com> 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);
>> > - if (par->mtrr_aper >= 0 && !par->aux_start) {
>> > - /* Make a hole for mmio. */
>> > - par->mtrr_reg = mtrr_add(par->res_start + 0x800000 -
>> > - GUI_RESERVE, GUI_RESERVE,
>> > - MTRR_TYPE_UNCACHABLE, 1);
>> > - if (par->mtrr_reg < 0) {
>> > - mtrr_del(par->mtrr_aper, 0, 0);
>> > - par->mtrr_aper = -1;
>> > - }
>> > - }
>> > }
>> > #endif
>> >
>> > @@ -2776,10 +2765,6 @@ aty_init_exit:
>> > par->pll_ops->set_pll(info, &par->saved_pll);
>> >
>> > #ifdef CONFIG_MTRR
>> > - if (par->mtrr_reg >= 0) {
>> > - mtrr_del(par->mtrr_reg, 0, 0);
>> > - par->mtrr_reg = -1;
>> > - }
>> > if (par->mtrr_aper >= 0) {
>> > mtrr_del(par->mtrr_aper, 0, 0);
>> > par->mtrr_aper = -1;
>> > @@ -3466,7 +3451,7 @@ static int atyfb_setup_generic(struct pci_dev *pdev, struct fb_info *info,
>> > }
>> >
>> > info->fix.mmio_start = raddr;
>> > - par->ati_regbase = ioremap(info->fix.mmio_start, 0x1000);
>> > + par->ati_regbase = ioremap_nocache(info->fix.mmio_start, 0x1000);
>>
>> Double-check me, but I think that ioremap_nocache + WC MTRR = WC.
>
> Precicely, in this case the WC hole was obtained by using MTRR WC. This
> patch removes that WC hole trick and now we can be explciit about
> only wanting ioremap_nocache() on the registers, that is WC is not
> desired here and is not used. The patch does not highlight the fact
> that there was left in place another ioremap() call for the framebuffer:
>
> info->screen_base = ioremap(info->fix.smem_start, info->fix.smem_len);
>
> That is the one that later after this patch we use ioremap_wc() for.
> This patch just removes the hole solution. That's all.
>

I don't understand.

If I read it right, there's a 2^n byte BAR. You're requesting WC for
the whole think using arch_phys_wc_add. On a PAT system that has no
effect and all is well. On a non-PAT system, it adds an MTRR. That
means that you need to override the MTRR somehow for the mmio regs,
and UC- won't do the trick.

Or am I missing something here?

--Andy

> Luis

--
Andy Lutomirski
AMA Capital Management, LLC