Re: [PATCH v2] drm/i915/gt: prevent forcewake releases during BAR resize

[Andrzej Hajda <andrzej.hajda@xxxxxxxxx>]

On 08.03.2023 18:29, Das, Nirmoy wrote:
> On 3/8/2023 2:36 PM, Andrzej Hajda wrote:
> > Tests on DG2 machines show that releasing forcewakes during BAR resize
> > results later in forcewake ack timeouts.
> Do we have a fdo/issues url for that? Having that as References would be 
> nice.

The patch is result of issue reported internally, but...grepping 
bugtracker I've found potential candidates:

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6530
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/7853

Maybe it would be good to add them on merge.
Anyway thx for a-b.

Regards
Andrzej

> >   Since forcewakes can be realeased
> > asynchronously the simplest way to prevent it is to get all forcewakes
> > for duration of BAR resizing.
> >
> > v2: hold rpm as well during resizing (Rodrigo)
> >
> > Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
>
>
> Acked-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
>
>
> > ---
> > Please ignore resend of v1, my mistake.
> >
> > Regards
> > Andrzej
> > ---
> >   drivers/gpu/drm/i915/gt/intel_region_lmem.c | 25 +++++++++++++++------
> >   1 file changed, 18 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_region_lmem.c 
> > b/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> > index 89fdfc67f8d1e0..2a3217e2890fc7 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> > @@ -54,6 +54,7 @@ static void i915_resize_lmem_bar(struct 
> > drm_i915_private *i915, resource_size_t
> >       struct resource *root_res;
> >       resource_size_t rebar_size;
> >       resource_size_t current_size;
> > +    intel_wakeref_t wakeref;
> >       u32 pci_cmd;
> >       int i;
> > @@ -102,15 +103,25 @@ static void i915_resize_lmem_bar(struct 
> > drm_i915_private *i915, resource_size_t
> >           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);
> > +    /*
> > +     * Releasing forcewake during BAR resizing results in later 
> > forcewake
> > +     * ack timeouts and former can happen any time - it is asynchronous.
> > +     * Grabbing all forcewakes prevents it.
> > +     */
> > +    with_intel_runtime_pm(i915->uncore.rpm, wakeref) {
> > +        intel_uncore_forcewake_get(&i915->uncore, FORCEWAKE_ALL);
> > -    _resize_bar(i915, GEN12_LMEM_BAR, rebar_size);
> > +        /* 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);
> > -    pci_assign_unassigned_bus_resources(pdev->bus);
> > -    pci_write_config_dword(pdev, PCI_COMMAND, pci_cmd);
> > +        _resize_bar(i915, GEN12_LMEM_BAR, rebar_size);
> > +
> > +        pci_assign_unassigned_bus_resources(pdev->bus);
> > +        pci_write_config_dword(pdev, PCI_COMMAND, pci_cmd);
> > +        intel_uncore_forcewake_put(&i915->uncore, FORCEWAKE_ALL);
> > +    }
> >   }
> >   #else
> >   static void i915_resize_lmem_bar(struct drm_i915_private *i915, 
> > resource_size_t lmem_size) {}