Re: [RFC PATCH 12/19] arm/gic: Add VPENDBASER/VPROPBASER accessors

[Mykola Kvach <xakep.amatop@xxxxxxxxx>]

Hi Mykyta,

Thank you for the patch!

On Mon, Feb 2, 2026 at 6:14 PM Mykyta Poturai <Mykyta_Poturai@xxxxxxxx> wrote:
>
> Implement accessors for GICv4 registers VPENDBASER and VPROPBASER.
> VPENDBASER access needs special handling to clear the Valid bit before
> writing a new value.
>
> Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>
> ---
>  xen/arch/arm/include/asm/gic_v4_its.h | 38 +++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
>
> diff --git a/xen/arch/arm/include/asm/gic_v4_its.h 
> b/xen/arch/arm/include/asm/gic_v4_its.h
> index fb0ef37bbe..ba81b25bde 100644
> --- a/xen/arch/arm/include/asm/gic_v4_its.h
> +++ b/xen/arch/arm/include/asm/gic_v4_its.h
> @@ -17,6 +17,8 @@
>   * along with this program; If not, see <http://www.gnu.org/licenses/>.
>   */
>
> +#include <asm/arm64/io.h>
> +
>  #ifndef __ASM_ARM_GICV4_ITS_H__
>  #define __ASM_ARM_GICV4_ITS_H__
>
> @@ -50,6 +52,42 @@ struct event_vlpi_map {
>  };
>
>  void gicv4_its_vpeid_allocator_init(void);
> +
> +#define GICR_VPROPBASER                              0x0070
> +#define GICR_VPENDBASER                              0x0078
> +
> +#define GICR_VPENDBASER_Dirty                   (1UL << 60)
> +#define GICR_VPENDBASER_PendingLast             (1UL << 61)
> +#define GICR_VPENDBASER_IDAI                    (1UL << 62)
> +#define GICR_VPENDBASER_Valid                   (1UL << 63)
> +
> +#define GICR_VPENDBASER_OUTER_CACHEABILITY_SHIFT         56
> +#define GICR_VPENDBASER_SHAREABILITY_SHIFT               10
> +#define GICR_VPENDBASER_INNER_CACHEABILITY_SHIFT          7
> +
> +#define gits_read_vpropbaser(c)         readq_relaxed(c)
> +#define gits_write_vpropbaser(v, c)     {writeq_relaxed(v, c);}
> +
> +/*
> + * GICR_VPENDBASER - the Valid bit must be cleared before changing
> + * anything else.
> + */
> +static inline void gits_write_vpendbaser(uint64_t val, void __iomem *addr)
> +{
> +    uint64_t tmp;
> +
> +    tmp = readq_relaxed(addr);
> +    while ( tmp & GICR_VPENDBASER_Valid )

The loop clearing GICR_VPENDBASER_Valid has no timeout.
If the bit never clears, we can spin forever. Please add a bounded
retry (and warn on timeout), similar to other polling paths.


Best regards,
Mykola

> +    {
> +        tmp &= ~GICR_VPENDBASER_Valid;
> +        writeq_relaxed(tmp, addr);
> +        tmp = readq_relaxed(addr);
> +    }
> +
> +    writeq_relaxed(val, addr);
> +}
> +#define gits_read_vpendbaser(c)     readq_relaxed(c)
> +
>  #endif
>
>  /*
> --
> 2.51.2