[{"id":3688718,"web_url":"http://patchwork.ozlabs.org/comment/3688718/","msgid":"<2f736c44-47dd-4573-b3c0-1bf5d9de475b@linaro.org>","list_archive_url":null,"date":"2026-05-08T20:36:48","subject":"Re: [PATCH 1/4] hw/misc/bcm2835_control.c: Don't assert on local\n timer zero reload value","submitter":{"id":72104,"url":"http://patchwork.ozlabs.org/api/people/72104/","name":"Richard Henderson","email":"richard.henderson@linaro.org"},"content":"On 5/8/26 11:20, Peter Maydell wrote:\n> The bcm2836 local timer has a basic \"counts down, fires at zero,\n> and reloads to programmed value to count down again\" functionality,\n> as documented in\n> https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2836/QA7_rev3.4.pdf\n> \n> The documentation is very sparse and doesn't say what actually\n> happens if the guest programs the reload value to zero. Currently we\n> trip an assert in this case.\n> \n> Instead, log this as a guest error and disable the timer (which seems\n> a reasonable guess -- effectively the timer will stop counting).\n> \n> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3395\n> Signed-off-by: Peter Maydell \n> ---\n> hw/intc/bcm2836_control.c | 15 ++++++++++++---\n> 1 file changed, 12 insertions(+), 3 deletions(-)\n\nThe alternate interpretation is that the timer continually raises interrupts, in which \ncase logging a guest error would be doubly appropriate.\n\nAnyway,\nReviewed-by: Richard Henderson \n\n\nr~\n\n> \n> diff --git a/hw/intc/bcm2836_control.c b/hw/intc/bcm2836_control.c\n> index f1deafaf7a..d6c6057cd2 100644\n> --- a/hw/intc/bcm2836_control.c\n> +++ b/hw/intc/bcm2836_control.c\n> @@ -197,12 +197,21 @@ static void bcm2836_control_local_timer_set_next(void *opaque)\n> {\n> BCM2836ControlState *s = opaque;\n> uint64_t next_event;\n> + uint64_t reload_value = LOCALTIMER_VALUE(s->local_timer_control);\n> \n> - assert(LOCALTIMER_VALUE(s->local_timer_control) > 0);\n> + if (reload_value == 0) {\n> + /*\n> + * Spec doesn't say what happens in this case; treat as a\n> + * guest error and stop the timer running.\n> + */\n> + qemu_log_mask(LOG_GUEST_ERROR, \"%s: local timer reload value is 0\\n\",\n> + __func__);\n> + timer_del(&s->timer);\n> + return;\n> + }\n> \n> next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +\n> - muldiv64(LOCALTIMER_VALUE(s->local_timer_control),\n> - NANOSECONDS_PER_SECOND, LOCALTIMER_FREQ);\n> + muldiv64(reload_value, NANOSECONDS_PER_SECOND, LOCALTIMER_FREQ);\n> timer_mod(&s->timer, next_event);\n> }\n>","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=qZOe4CNc;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists1p.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4gC1Br5HS4z1yCg\n\tfor ; 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