Hi Alexandru,
On 11/25/20 4:51 PM, Alexandru Elisei wrote:
> The GICv3 driver executes a DSB barrier before sending an IPI, which
> ensures that memory accesses have completed. This removes the need to
> enforce ordering with respect to stats_reset() in the IPI handler.
>
> For GICv2, we still need the DMB to ensure ordering between the read of the
> GICC_IAR MMIO register and the read from the acked array. It also matches
> what the Linux GICv2 driver does in gic_handle_irq().
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> ---
> arm/gic.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arm/gic.c b/arm/gic.c
> index 4e947e8516a2..7befda2a8673 100644
> --- a/arm/gic.c
> +++ b/arm/gic.c
> @@ -60,7 +60,6 @@ static void stats_reset(void)
> bad_sender[i] = -1;
> bad_irq[i] = -1;
> }
> - smp_wmb();
Here we are (pair removed). Still the one in check_acked still exists.
> }
>
> static void check_acked(const char *testname, cpumask_t *mask)
> @@ -150,7 +149,13 @@ static void ipi_handler(struct pt_regs *regs __unused)
>
> if (irqnr != GICC_INT_SPURIOUS) {
> gic_write_eoir(irqstat);
> - smp_rmb(); /* pairs with wmb in stats_reset */
> + /*
> + * Make sure data written before the IPI was triggered is
> + * observed after the IAR is read. Pairs with the smp_wmb
> + * when sending the IPI.
> + */
> + if (gic_version() == 2)
> + smp_rmb();
> ++acked[smp_processor_id()];
> check_ipi_sender(irqstat);
> check_irqnr(irqnr);
>
Thanks
Eric
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