Re: [PATCH v2 17/17] drm/i915: Properly request PCI BARs

Ville Syrjälä
2020-10-09T09:48:04Z

On Fri, Oct 09, 2020 at 09:59:34AM +0200, Daniel Vetter wrote:
> When trying to test my CONFIG_IO_STRICT_DEVMEM changes I realized they
> do nothing for i915. Because i915 doesn't request any regions, like
> pretty much all drm pci drivers. I guess this is some very old
> remnants from the userspace modesetting days, when we wanted to
> co-exist with the fbdev driver. Which usually requested these
> resources.
>
> But makes me wonder why the pci subsystem doesn't just request
> resource automatically when we map a bar and a pci driver is bound?
>
> Knowledge about which pci bars we need kludged together from
> intel_uncore.c and intel_gtt.c from i915 and intel-gtt.c over in the
> fake agp driver.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: linux-mm@kvack.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-samsung-soc@vger.kernel.org
> Cc: linux-media@vger.kernel.org
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: linux-pci@vger.kernel.org
> ---
> drivers/gpu/drm/i915/intel_uncore.c | 25 +++++++++++++++++++++++--
> 1 file changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 54e201fdeba4..ce39049d8919 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1692,10 +1692,13 @@ static int uncore_mmio_setup(struct intel_uncore *uncore)
> struct pci_dev *pdev = i915->drm.pdev;
> int mmio_bar;
> int mmio_size;
> + int bar_selection;

Signed bitmasks always make me uneasy. But looks like
that's what it is in the pci api. So meh.

> + int ret;
>
> mmio_bar = IS_GEN(i915, 2) ? 1 : 0;
> + bar_selection = BIT (2) | BIT(mmio_bar);
^
spurious space

That's also not correct for gen2 I think.

gen2:
0 = GMADR
1 = MMADR
2 = IOBAR

gen3:
0 = MMADR
1 = IOBAR
2 = GMADR
3 = GTTADR

gen4+:
0+1 = GTTMMADR
2+3 = GMADR
4 = IOBAR

Maybe we should just have an explicit list of bars like that in a
comment?

I'd also suggest sucking this bitmask calculation into a small helper
so you can reuse it for the release.

> /*
> - * Before gen4, the registers and the GTT are behind different BARs.
> + * On gen3 the registers and the GTT are behind different BARs.
> * However, from gen4 onwards, the registers and the GTT are shared
> * in the same BAR, so we want to restrict this ioremap from
> * clobbering the GTT which we want ioremap_wc instead. Fortunately,
> @@ -1703,6 +1706,8 @@ static int uncore_mmio_setup(struct intel_uncore *uncore)
> * generations up to Ironlake.
> * For dgfx chips register range is expanded to 4MB.
> */
> + if (INTEL_GEN(i915) == 3)
> + bar_selection |= BIT(3);
> if (INTEL_GEN(i915) < 5)
> mmio_size = 512 * 1024;
> else if (IS_DGFX(i915))
> @@ -1710,8 +1715,15 @@ static int uncore_mmio_setup(struct intel_uncore *uncore)
> else
> mmio_size = 2 * 1024 * 1024;
>
> + ret = pci_request_selected_regions(pdev, bar_selection, "i915");
> + if (ret < 0) {
> + drm_err(&i915->drm, "failed to request pci bars\n");
> + return ret;
> + }
> +
> uncore->regs = pci_iomap(pdev, mmio_bar, mmio_size);
> if (uncore->regs == NULL) {
> + pci_release_selected_regions(pdev, bar_selection);
> drm_err(&i915->drm, "failed to map registers\n");
> return -EIO;
> }
> @@ -1721,9 +1733,18 @@ static int uncore_mmio_setup(struct intel_uncore *uncore)
>
> static void uncore_mmio_cleanup(struct intel_uncore *uncore)
> {
> - struct pci_dev *pdev = uncore->i915->drm.pdev;
> + struct drm_i915_private *i915 = uncore->i915;
> + struct pci_dev *pdev = i915->drm.pdev;
> + int mmio_bar;
> + int bar_selection;
> +
> + mmio_bar = IS_GEN(i915, 2) ? 1 : 0;
> + bar_selection = BIT (2) | BIT(mmio_bar);
> + if (INTEL_GEN(i915) == 3)
> + bar_selection |= BIT(3);
>
> pci_iounmap(pdev, uncore->regs);
> + pci_release_selected_regions(pdev, bar_selection);
> }
>
> void intel_uncore_init_early(struct intel_uncore *uncore,
> --
> 2.28.0
>
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--
Ville Syrjälä
Intel