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SubjectRE: [Intel-gfx] [PATCH 1/2] drm/i915: Add support for LMEM PCIe resizable bar
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> -----Original Message-----
> From: Christian König <christian.koenig@amd.com>
> Sent: 18 June 2022 08:45 PM
> To: De Marchi, Lucas <lucas.demarchi@intel.com>; Bjorn Helgaas
> <helgaas@kernel.org>
> Cc: linux-pci@vger.kernel.org; intel-gfx@lists.freedesktop.org; Sergei
> Miroshnichenko <s.miroshnichenko@yadro.com>; linux-
> kernel@vger.kernel.org; Dandamudi, Priyanka
> <priyanka.dandamudi@intel.com>; Auld, Matthew
> <matthew.auld@intel.com>; Bjorn Helgaas <bhelgaas@google.com>
> Subject: Re: [Intel-gfx] [PATCH 1/2] drm/i915: Add support for LMEM PCIe
> resizable bar
>
> Am 17.06.22 um 23:27 schrieb Lucas De Marchi:
> > On Fri, Jun 17, 2022 at 03:32:52PM -0500, Bjorn Helgaas wrote:
> >> [+cc Christian, author of pci_resize_resource(), Sergei, author of
> >> rebalancing patches]
> >>
> >> Hi Lucas,
> >>
> >> On Fri, Jun 17, 2022 at 11:44:41AM -0700, Lucas De Marchi wrote:
> >>> Cc'ing intel-pci, lkml, Bjorn
> >>>
> >>> On Fri, Jun 17, 2022 at 11:32:37AM +0300, Jani Nikula wrote:
> >>> > On Thu, 16 Jun 2022, priyanka.dandamudi@intel.com wrote:
> >>> > > From: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
> >>> > >
> >>> > > Add support for the local memory PICe resizable bar, so that
> >>> > > local memory can be resized to the maximum size supported by the
> >>> device,
> >>> > > and mapped correctly to the PCIe memory bar. It is usual that
> >>> > > GPU devices expose only 256MB BARs primarily to be compatible
> >>> > > with
> >>> 32-bit
> >>> > > systems. So, those devices cannot claim larger memory BAR
> >>> windows size due
> >>> > > to the system BIOS limitation. With this change, it would be
> >>> possible to
> >>> > > reprogram the windows of the bridge directly above the
> >>> requesting device
> >>> > > on the same BAR type.
> >>>
> >>> There is a big caveat here that this may be too late as other
> >>> drivers may have already mapped their BARs - so probably too late in
> >>> the pci scan for it to be effective. In fact, after using this for a
> >>> while, it seems to fail too often, particularly on CFL systems.
> >>
> >> Help me understand the "too late" part.  Do you mean that there is
> >> enough available space for the max BAR size, but it's fragmented and
> >> therefore not usable?  And that if we could do something earlier,
> >> before drivers have claimed their devices, we might be able to
> >> compact the BARs of other devices to make a larger contiguous available
> space?
> >
> > yes. I will dig some logs I had in the past to confirm.
> >
> >
> >> That is theoretically possible, but I think the current
> >> pci_resize_resource() only supports resizing of the specified BAR and
> >> any upstream bridge windows.  I don't think it supports moving BARs
> >> of other devices.
> >>
> >> Sergei did some nice work that might help with this situation because
> >> it can move BARs around more generally.  It hasn't quite achieved
> >> critical mass yet, but maybe this would help get there:
> >>
> >>
> >>
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flor
> >> e.kernel.org%2Flinux-pci%2F20201218174011.340514-1-
> s.miroshnichenko%4
> >>
> 0yadro.com%2F&amp;data=05%7C01%7Cchristian.koenig%40amd.com%7C8
> 096027
> >>
> f68484d0656b108da50a82e7d%7C3dd8961fe4884e608e11a82d994e183d%7C
> 0%7C0%
> >>
> 7C637910980509199388%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjA
> wMDAiLCJQ
> >>
> IjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;
> sdata=
> >>
> %2FfntE2FTQ8wmLnz4wnzk94R0GMLEwVs7Mj18%2B9Q6PJk%3D&amp;reser
> ved=0
> >>
> >
> > oh... I hadn't thought about pause/ioremap/unpause. That looks rad :).
> > So it seems this would integrate neatly with
> > pci_resize_resource() (what this patch is doing), as long as drivers
> > for devices affected implement
> > .bar_fixed()/.rescan_prepare()/.rescan_done(). That seems it would
> > solve our issues too.
>
> Well we never ran into any of the issues you describe with PCIe BAR resize
> for GPUs so there must be something you do differently to AMD hardware
> regarding this.
>
> Additional to that keep in mind that you can't resize the BAR before kicking
> out vgacon/efifb or otherwise it can happen that the just released 256MiB
> window is still used while you try to resize it. When you do that you usually
> end up with a hard lockup of the system.
>
> Regards,
> Christian.
>
> >
> > thanks
> > Lucas De Marchi
> >
> >>
> >> If I understand Sergei's series correctly, this rebalancing actually
> >> cannot be done during enumeration because we only move BARs if a
> >> driver for the device indicates that it supports it, so there would
> >> be no requirement to do this early.
> >>
> >>> Do we have any alternative to be done in the PCI subsystem during
> >>> the scan?  There is other work in progress to allow i915 to use the
> >>> rest of the device memory even with a smaller BAR, but it would be
> >>> better if we can improve our chances of succeeding the resize.
> >>
> >>> > > Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
> >>> > > Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
> >>> > > Cc: Stuart Summers <stuart.summers@intel.com>
> >>> > > Cc: Michael J Ruhl <michael.j.ruhl@intel.com>
> >>> > > Cc: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
> >>> > > Signed-off-by: Priyanka Dandamudi
> <priyanka.dandamudi@intel.com>
> >>> > > Reviewed-by: Matthew Auld <matthew.auld@intel.com>
> >>> >
> >>> > Please see
> >>>
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flo
> >>>
> re.kernel.org%2Fr%2F87pmj8vesm.fsf%40intel.com&amp;data=05%7C01%7C
> ch
> >>>
> ristian.koenig%40amd.com%7C8096027f68484d0656b108da50a82e7d%7C3d
> d896
> >>>
> 1fe4884e608e11a82d994e183d%7C0%7C0%7C637910980509199388%7CUnk
> nown%7C
> >>>
> TWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiL
> CJX
> >>>
> VCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=d4cf7HQ6t7y1Xobwjdt8im%
> 2Fh0E5IZ
> >>> sXgzQDpsB2vCU4%3D&amp;reserved=0
> >>> >
> >>> > > ---
> >>> > >  drivers/gpu/drm/i915/i915_driver.c | 92
> >>> ++++++++++++++++++++++++++++++
> >>> > >  1 file changed, 92 insertions(+)
> >>> > >
> >>> > > diff --git a/drivers/gpu/drm/i915/i915_driver.c
> >>> b/drivers/gpu/drm/i915/i915_driver.c
> >>> > > index d26dcca7e654..4bdb471cb2e2 100644
> >>> > > --- a/drivers/gpu/drm/i915/i915_driver.c
> >>> > > +++ b/drivers/gpu/drm/i915/i915_driver.c
> >>> > > @@ -303,6 +303,95 @@ static void sanitize_gpu(struct
> >>> drm_i915_private *i915)
> >>> > >          __intel_gt_reset(to_gt(i915), ALL_ENGINES);
> >>> > >  }
> >>> > >
> >>> > > +static void __release_bars(struct pci_dev *pdev) {
> >>> > > +    int resno;
> >>> > > +
> >>> > > +    for (resno = PCI_STD_RESOURCES; resno <
> >>> PCI_STD_RESOURCE_END; resno++) {
> >>> > > +        if (pci_resource_len(pdev, resno))
> >>> > > +            pci_release_resource(pdev, resno);
> >>> > > +    }
> >>> > > +}
> >>> > > +
> >>> > > +static void
> >>> > > +__resize_bar(struct drm_i915_private *i915, int resno,
> >>> resource_size_t size)
> >>> > > +{
> >>> > > +    struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
> >>> > > +    int bar_size = pci_rebar_bytes_to_size(size);
> >>> > > +    int ret;
> >>> > > +
> >>> > > +    __release_bars(pdev);
> >>> > > +
> >>> > > +    ret = pci_resize_resource(pdev, resno, bar_size);
> >>> > > +    if (ret) {
> >>> > > +        drm_info(&i915->drm, "Failed to resize BAR%d to %dM
> >>> (%pe)\n",
> >>> > > +             resno, 1 << bar_size, ERR_PTR(ret));
> >>> > > +        return;
> >>> > > +    }
> >>> > > +
> >>> > > +    drm_info(&i915->drm, "BAR%d resized to %dM\n", resno, 1 <<
> >>> bar_size);
> >>> > > +}
> >>> > > +
> >>> > > +/* BAR size starts from 1MB - 2^20 */ #define BAR_SIZE_SHIFT 20
> >>> > > +static resource_size_t __lmem_rebar_size(struct
> >>> > > +drm_i915_private *i915, int resno) {
> >>> > > +    struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
> >>> > > +    u32 rebar = pci_rebar_get_possible_sizes(pdev, resno);
> >>> > > +    resource_size_t size;
> >>> > > +
> >>> > > +    if (!rebar)
> >>> > > +        return 0;
> >>> > > +
> >>> > > +    size = 1ULL << (__fls(rebar) + BAR_SIZE_SHIFT);
> >>> > > +
> >>> > > +    if (size <= pci_resource_len(pdev, resno))
> >>> > > +        return 0;
> >>> > > +
> >>> > > +    return size;
> >>> > > +}
> >>> > > +
> >>> > > +#define LMEM_BAR_NUM 2
> >>> > > +static void i915_resize_lmem_bar(struct drm_i915_private *i915)
> >>> > > +{
> >>> > > +    struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
> >>> > > +    struct pci_bus *root = pdev->bus;
> >>> > > +    struct resource *root_res;
> >>> > > +    resource_size_t rebar_size = __lmem_rebar_size(i915,
> >>> LMEM_BAR_NUM);
> >>> > > +    u32 pci_cmd;
> >>> > > +    int i;
> >>> > > +
> >>> > > +    if (!rebar_size)
> >>> > > +        return;
> >>> > > +
> >>> > > +    /* Find out if root bus contains 64bit memory addressing */
> >>> > > +    while (root->parent)
> >>> > > +        root = root->parent;
> >>> > > +
> >>> > > +    pci_bus_for_each_resource(root, root_res, i) {
> >>> > > +        if (root_res && root_res->flags & (IORESOURCE_MEM |
> >>> > > +                    IORESOURCE_MEM_64) && root_res->start >
> >>> 0x100000000ull)
> >>> > > +            break;
> >>> > > +    }
> >>> > > +
> >>> > > +    /* pci_resize_resource will fail anyways */
> >>> > > +    if (!root_res) {
> >>> > > +        drm_info(&i915->drm, "Can't resize LMEM BAR - platform
> >>> support is missing\n");
> >>> > > +        return;
> >>> > > +    }
> >>> > > +
> >>> > > +    /* First disable PCI memory decoding references */
> >>> > > +    pci_read_config_dword(pdev, PCI_COMMAND, &pci_cmd);
> >>> > > +    pci_write_config_dword(pdev, PCI_COMMAND,
> >>> > > +                   pci_cmd & ~PCI_COMMAND_MEMORY);
> >>> > > +
> >>> > > +    __resize_bar(i915, LMEM_BAR_NUM, rebar_size);
> >>> > > +
> >>> > > + pci_assign_unassigned_bus_resources(pdev->bus);
> >>> > > +    pci_write_config_dword(pdev, PCI_COMMAND, pci_cmd); }
> >>> > > +
> >>> > >  /**
> >>> > >   * i915_driver_early_probe - setup state not requiring device
> >>> access
> >>> > >   * @dev_priv: device private
> >>> > > @@ -852,6 +941,9 @@ int i915_driver_probe(struct pci_dev *pdev,
> >>> const struct pci_device_id *ent)
> >>> > >
> >>> > > disable_rpm_wakeref_asserts(&i915->runtime_pm);
> >>> > >
> >>> > > +    if (HAS_LMEM(i915))
> >>> > > +        i915_resize_lmem_bar(i915);
> >>> > > +
> >>> > >      intel_vgpu_detect(i915);
> >>> > >
> >>> > >      ret = intel_gt_probe_all(i915);
> >>> >
> >>> > --
> >>> > Jani Nikula, Intel Open Source Graphics Center

[Dandamudi, Priyanka]
@De Marchi, Lucas
Can I proceed with the current approach or is there anything I need to add to it?
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