Re: [PATCH v3 4/4] xen/arm: its: handle dma-noncoherent on GIC and ITS nodes

[Mykola Kvach <xakep.amatop@xxxxxxxxx>]

On Wed, Sep 23, 2026 at 3:30 AM Volodymyr Babchuk
<Volodymyr_Babchuk@xxxxxxxx> wrote:
>
> Hi,
>
> Mykola Kvach <mykola_kvach@xxxxxxxx> writes:
>
> > The DT dma-noncoherent property describes the bus coherency of the
> > device represented by the node. On an ITS subnode, that is memory
> > accessed by that ITS. Add GICV3_QUIRK_MEM_NC_NS to the corresponding
> > host_its and use it when programming GITS_CBASER and GITS_BASER<n>.
> >
> > On the top-level GIC node, the property describes the Redistributor side
> > of the LPI path. Collect it in gicv3_lpi_init_host_lpis() and apply it
> > only to the host LPI policy used when allocating the property and
> > pending tables and when programming GICR_PROPBASER and GICR_PENDBASER.
> > Mark the function init-only because firmware attributes are collected
> > only during boot.
> >
> > Do not inherit the property between parent and child nodes: ITS-node
> > non-coherency does not change the global host LPI policy, and GIC-node
> > non-coherency does not change per-ITS quirk_flags.
> >
> > ACPI is unchanged; this patch only consumes the DT dma-noncoherent
> > property.
> >
> > Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
> > ---
> > Changes in v3:
> > - Keep the ITS init annotations with the earlier initialization patch.
> > - Drop the redundant aggregate host-LPI-flags message.
> >
> > Changes in v2:
> > - Split v1's dma-noncoherent handling into explicit ITS-node and GIC-node
> >   scopes.
> > - Apply an ITS subnode property only to the matching host_its
> >   quirk_flags.
> > - Collect the top-level GIC property from gic-v3-lpi.c before host LPI
> >   allocations use host_lpi_flags.
> > ---
> >  xen/arch/arm/gic-v3-its.c | 17 +++++++++++++++++
> >  xen/arch/arm/gic-v3-lpi.c | 20 +++++++++++++++++++-
> >  2 files changed, 36 insertions(+), 1 deletion(-)
> >
> > diff --git a/xen/arch/arm/gic-v3-its.c b/xen/arch/arm/gic-v3-its.c
> > index f52232ca40..6734f94e7c 100644
> > --- a/xen/arch/arm/gic-v3-its.c
> > +++ b/xen/arch/arm/gic-v3-its.c
> > @@ -139,6 +139,21 @@ static const struct its_quirk *__init 
> > gicv3_its_find_quirk(
> >      return NULL;
> >  }
> >
> > +static void __init gicv3_its_collect_fw_attrs(struct host_its *hw_its)
> > +{
> > +    /*
> > +     * An ITS subnode property describes memory transactions made by that 
> > ITS.
> > +     * Do not inherit it into the global host LPI/Redistributor policy.
> > +     */
> > +    if ( !hw_its->dt_node ||
> > +         !dt_property_read_bool(hw_its->dt_node, "dma-noncoherent") )
> > +        return;
> > +
> > +    hw_its->quirk_flags |= GICV3_QUIRK_MEM_NC_NS;
> > +    printk("GICv3: ITS @%#"PRIpaddr" marked dma-noncoherent\n",
> > +           hw_its->addr);
> > +}
> > +
> >  static void __init gicv3_its_collect_quirks(struct host_its *hw_its)
> >  {
> >      const struct its_quirk *quirk = gicv3_its_find_quirk(hw_its);
> > @@ -149,6 +164,8 @@ static void __init gicv3_its_collect_quirks(struct 
> > host_its *hw_its)
> >          gicv3_lpi_update_host_flags(quirk->lpi_flags);
> >          printk("GICv3: enabling workaround for ITS: %s\n", quirk->desc);
> >      }
> > +
> > +    gicv3_its_collect_fw_attrs(hw_its);
> >  }
> >
> >  uint64_t gicv3_mem_get_cacheability(uint32_t flags)
> > diff --git a/xen/arch/arm/gic-v3-lpi.c b/xen/arch/arm/gic-v3-lpi.c
> > index accfd48a74..1cf49430ea 100644
> > --- a/xen/arch/arm/gic-v3-lpi.c
> > +++ b/xen/arch/arm/gic-v3-lpi.c
> > @@ -7,7 +7,9 @@
> >   * Copyright (C) 2016,2017 - ARM Ltd
> >   */
> >
> > +#include <xen/acpi.h>
> >  #include <xen/cpu.h>
> > +#include <xen/device_tree.h>
> >  #include <xen/init.h>
> >  #include <xen/lib.h>
> >  #include <xen/mm.h>
> > @@ -102,6 +104,20 @@ void __init gicv3_lpi_update_host_flags(uint32_t flags)
> >      host_lpi_flags |= flags;
> >  }
> >
> > +static void __init gicv3_lpi_collect_fw_attrs(void)
> > +{
> > +    /*
> > +     * A top-level GIC node property describes the Redistributor side of 
> > the
> > +     * LPI path. Do not inherit it into per-ITS policy.
> > +     */
> > +    if ( !acpi_disabled ||
> > +         !dt_property_read_bool(dt_interrupt_controller, 
> > "dma-noncoherent") )
> > +        return;
> > +
> > +    gicv3_lpi_update_host_flags(GICV3_QUIRK_MEM_NC_NS);
> > +    printk("GICv3: Redistributors marked dma-noncoherent\n");
> > +}
> > +
> >  static union host_lpi *gic_get_host_lpi(uint32_t plpi)
> >  {
> >      union host_lpi *block;
> > @@ -443,7 +459,7 @@ integer_param("max_lpi_bits", max_lpi_bits);
> >   * to the page with the actual "union host_lpi" entries. Our LPI limit
> >   * avoids excessive memory usage.
> >   */
> > -int gicv3_lpi_init_host_lpis(unsigned int host_lpi_bits)
> > +int __init gicv3_lpi_init_host_lpis(unsigned int host_lpi_bits)
>
> Spurious change?

This is intentional. This patch adds a call to the __init helper
gicv3_lpi_collect_fw_attrs(). gicv3_lpi_init_host_lpis() is only
called during boot, from gicv3_its_init(), so I marked it __init
as well.

Best regards,
Mykola