Re: [PATCH v2 4/4] xen/arm: its: handle dma-noncoherent on GIC and ITS nodes

[Mykola Kvach <mykola_kvach@epam.com>]

On Fri, Jul 31, 2026 at 10:39:54AM +0200, Orzel, Michal wrote:
> 
> 
> On 28-May-26 02:25, Mykola Kvach wrote:
> > From: Mykola Kvach <mykola_kvach@epam.com>
> > 
> > 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, so add GICV3_QUIRK_MEM_NC_NS to the corresponding host_its before
> > programming GITS tables and allocating ITTs.
> > 
> > When the property is present on the top-level GIC node, it 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
> > for GICR_PROPBASER and GICR_PENDBASER setup.
> > 
> > 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 left unchanged; this patch only consumes the DT dma-noncoherent
> > property.
> > 
> > Signed-off-by: Mykola Kvach <mykola_kvach@epam.com>
> > ---
> > 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 | 21 +++++++++++++++++++--
> >  xen/arch/arm/gic-v3-lpi.c | 22 +++++++++++++++++++++-
> >  2 files changed, 40 insertions(+), 3 deletions(-)
> > 
> > diff --git a/xen/arch/arm/gic-v3-its.c b/xen/arch/arm/gic-v3-its.c
> > index e055914763..606b127487 100644
> > --- a/xen/arch/arm/gic-v3-its.c
> > +++ b/xen/arch/arm/gic-v3-its.c
> > @@ -134,6 +134,21 @@ 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);
> > @@ -144,6 +159,8 @@ 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)
> > @@ -578,7 +595,7 @@ static int gicv3_disable_its(struct host_its *hw_its)
> >      return -ETIMEDOUT;
> >  }
> >  
> > -static int gicv3_its_init_single_its(struct host_its *hw_its)
> > +static int __init gicv3_its_init_single_its(struct host_its *hw_its)
> These __init additions have nothing to do with dma-noncoherent and
> are not mentioned in the commit message. They belong with patch 2/4,
> which is where the callees became __init.

I'll move the ITS __init annotations out of this patch and into the
replacement first patch, so they precede the init-only quirk collectors

> 
> >  {
> >      uint64_t reg;
> >      int i, ret;
> > @@ -1221,7 +1238,7 @@ static void gicv3_its_acpi_init(void)
> >  
> >  #endif
> >  
> > -int gicv3_its_init(void)
> > +int __init gicv3_its_init(void)
> >  {
> >      struct host_its *hw_its;
> >      int ret;
> > diff --git a/xen/arch/arm/gic-v3-lpi.c b/xen/arch/arm/gic-v3-lpi.c
> > index 35f93e4756..c6f17b9b2d 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/lib.h>
> >  #include <xen/mm.h>
> >  #include <xen/param.h>
> > @@ -101,6 +103,20 @@ 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: GIC node marked dma-noncoherent for host LPI tables\n");
> > +}
> > +
> >  static union host_lpi *gic_get_host_lpi(uint32_t plpi)
> >  {
> >      union host_lpi *block;
> > @@ -442,7 +458,7 @@ 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)
> >  {
> >      unsigned int nr_lpi_ptrs;
> >      int rc;
> > @@ -450,6 +466,10 @@ int gicv3_lpi_init_host_lpis(unsigned int host_lpi_bits)
> >      /* We rely on the data structure being atomically accessible. */
> >      BUILD_BUG_ON(sizeof(union host_lpi) > sizeof(unsigned long));
> >  
> > +    gicv3_lpi_collect_fw_attrs();
> > +    if ( host_lpi_flags )
> > +        printk("GICv3: host LPI workaround flags: %#x\n", host_lpi_flags);
> Every contributor to host_lpi_flags already prints its own line -
> "enabling workaround for ITS: %s" from the quirk path. Please drop this one.

I'll drop the aggregate host-LPI-flags message and keep the per-source
diagnostics.

Best regards,
Mykola