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GET /api/patches/2194968/?format=api
{ "id": 2194968, "url": "http://patchwork.ozlabs.org/api/patches/2194968/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260210101702.3980804-1-peter.maydell@linaro.org/", "project": { "id": 14, "url": "http://patchwork.ozlabs.org/api/projects/14/?format=api", "name": "QEMU Development", "link_name": "qemu-devel", "list_id": "qemu-devel.nongnu.org", "list_email": "qemu-devel@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260210101702.3980804-1-peter.maydell@linaro.org>", "list_archive_url": null, "date": "2026-02-10T10:17:02", "name": "hw/char/pl011: Only log \"data written to disabled UART\" once", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "275c43ccfd80aff96d369162785427579e7882f1", "submitter": { "id": 5111, "url": "http://patchwork.ozlabs.org/api/people/5111/?format=api", "name": "Peter Maydell", "email": "peter.maydell@linaro.org" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260210101702.3980804-1-peter.maydell@linaro.org/mbox/", "series": [ { "id": 491642, "url": "http://patchwork.ozlabs.org/api/series/491642/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=491642", "date": "2026-02-10T10:17:02", "name": "hw/char/pl011: Only log \"data written to disabled UART\" once", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/491642/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2194968/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2194968/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "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=Q1a7qSzH;\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=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)" ], "Received": [ "from lists.gnu.org (lists.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 4f9HZC3RWGz1xvb\n\tfor <incoming@patchwork.ozlabs.org>; Tue, 10 Feb 2026 21:17:55 +1100 (AEDT)", "from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from <qemu-devel-bounces@nongnu.org>)\n\tid 1vpknu-0001Ag-UH; Tue, 10 Feb 2026 05:17:10 -0500", "from eggs.gnu.org ([2001:470:142:3::10])\n by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <peter.maydell@linaro.org>)\n id 1vpknr-0001AH-Ef\n for qemu-devel@nongnu.org; Tue, 10 Feb 2026 05:17:08 -0500", "from mail-wm1-x329.google.com ([2a00:1450:4864:20::329])\n by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128)\n (Exim 4.90_1) (envelope-from <peter.maydell@linaro.org>)\n id 1vpknp-0002JJ-Pg\n for qemu-devel@nongnu.org; Tue, 10 Feb 2026 05:17:07 -0500", "by mail-wm1-x329.google.com with SMTP id\n 5b1f17b1804b1-4806cc07ce7so6094965e9.1\n for <qemu-devel@nongnu.org>; Tue, 10 Feb 2026 02:17:05 -0800 (PST)", "from lanath.. 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The idea is to note that the guest has done\nsomething dubious but let it work anyway. However, since we print\nthis message for every output character, it floods the logs when\nrunning a guest that does this.\n\nKeep a note of whether we've printed the log message or not, so we\nonly output it once. If the guest actively disables the UART, we\nre-arm the log message.\n\nNotably, the Linux kernel does not bother to enable the UART if it is\nused for earlycon, relying on the firmware having already done that.\n\nSigned-off-by: Peter Maydell <peter.maydell@linaro.org>\n---\nThe log messages here were getting in my way trying to debug something\nelse, but I didn't want to just delete them completely.\n\n hw/char/pl011.c | 24 ++++++++++++++++++++++--\n include/hw/char/pl011.h | 1 +\n 2 files changed, 23 insertions(+), 2 deletions(-)", "diff": "diff --git a/hw/char/pl011.c b/hw/char/pl011.c\nindex b2ca68e3e8..cb12c3e224 100644\n--- a/hw/char/pl011.c\n+++ b/hw/char/pl011.c\n@@ -227,10 +227,25 @@ static void pl011_loopback_tx(PL011State *s, uint32_t value)\n static void pl011_write_txdata(PL011State *s, uint8_t data)\n {\n if (!(s->cr & CR_UARTEN)) {\n- qemu_log_mask(LOG_GUEST_ERROR,\n- \"PL011 data written to disabled UART\\n\");\n+ /*\n+ * Only log this message once, not every time the guest outputs:\n+ * otherwise we would flood the logs with this message, making\n+ * harder to debug guests. (Some very popular guests like Linux\n+ * don't actively enable the UART.)\n+ */\n+ if (!s->logged_disabled_uart) {\n+ qemu_log_mask(LOG_GUEST_ERROR,\n+ \"PL011 data written to disabled UART\\n\");\n+ s->logged_disabled_uart = true;\n+ }\n }\n if (!(s->cr & CR_TXE)) {\n+ /*\n+ * We don't bother with the only-log-once machinery for this check\n+ * because TXE is enabled by default from PL011 reset, so there\n+ * isn't likely to be existing in-the-wild guest code that trips\n+ * over this one.\n+ */\n qemu_log_mask(LOG_GUEST_ERROR,\n \"PL011 data written to disabled TX UART\\n\");\n }\n@@ -457,6 +472,10 @@ static void pl011_write(void *opaque, hwaddr offset,\n break;\n case 12: /* UARTCR */\n /* ??? Need to implement the enable bit. */\n+ if ((s->cr ^ value) & CR_UARTEN) {\n+ /* Re-arm the log warning when the guest toggles UARTEN */\n+ s->logged_disabled_uart = false;\n+ }\n s->cr = value;\n pl011_loopback_mdmctrl(s);\n break;\n@@ -665,6 +684,7 @@ static void pl011_reset(DeviceState *dev)\n s->ifl = 0x12;\n s->cr = 0x300;\n s->flags = 0;\n+ s->logged_disabled_uart = false;\n pl011_reset_rx_fifo(s);\n pl011_reset_tx_fifo(s);\n }\ndiff --git a/include/hw/char/pl011.h b/include/hw/char/pl011.h\nindex ff735b5234..5695787650 100644\n--- a/include/hw/char/pl011.h\n+++ b/include/hw/char/pl011.h\n@@ -51,6 +51,7 @@ struct PL011State {\n qemu_irq irq[6];\n Clock *clk;\n bool migrate_clk;\n+ bool logged_disabled_uart;\n const unsigned char *id;\n /*\n * Since some users embed this struct directly, we must\n", "prefixes": [] }