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[2003:cf:573b:e100:32bb:d7f6:5fb9:9e30]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482a5b77f41sm3123140f8f.27.2026.08.17.04.33.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Aug 2026 04:33:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mihalicyn.com; s=mihalicyn; t=1786966431; x=1787571231; darn=nongnu.org; h=content-transfer-encoding:content-type:mime-version:message-id:date :subject:cc:to:from:from:to:cc:subject:date:message-id:reply-to :content-type; bh=+JRr5THd9V5FxcrPVZRC9o711BRF+tkcolc4gE+ntNk=; b=idYyp5a4aO1l9lUfirJQNezvj1/qC2AFWb4jNFHj0dsUmoB/OIzHrxa21R7JqdiIgQ coRBO91wHbkmPfsLWTpR5yDYom8hg+Yf6D9t1cX/PyhSVFKG77l6MANd8wvIItiEiR3c 0BKV4mDR4jdzv/c5lCcC2D0480yoo0MOqBV0Q= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786966431; x=1787571231; h=content-transfer-encoding:content-type:mime-version:message-id:date :subject:cc:to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to:content-type; bh=+JRr5THd9V5FxcrPVZRC9o711BRF+tkcolc4gE+ntNk=; b=shgUfpvMsGDZoxLhJYEhBNvFIfLnDEKI3TW2UCc0IeiVQxFLarQpZbDGIr6XxePF9V VGtdgip7EJuEi8FR3hUkZ3yPRmQL/fW+wI2214o+KvzbgeGxtitZ8d/2+W3xYqfoWpAP HMgoTGfGPHWgbQn2Rnu6Z4mYSJ6hADK6PHweDwDYXVoqvCZACplsX5py/3tWwqs7Ao3Z tG2cfJKp7/gdOQaj/ZvmtKHq7sDfe9Ph61d1bN5M6uKcIpfg85HrhoOaTTf8/2vrZdD2 ENz6ujtTY9p9F3MuS0oY1iWb9DoUymKPztcy37Axu/wGw6bALhaoo8bEJYA/0MIokeGD bLFg== X-Gm-Message-State: AOJu0YxY/bqMNSuYnbZQ6pfLKHdwHfWplAZB3zb3z4vNtngjXD6bsfOg iCkIeU3C+P3TT4GH8VaPYkQt4q4Ubiz1GROu3b1pDJRYWOnGQ5ncLO+zUkwypSFhBHHCedftF/v xSNVJ X-Gm-Gg: AR+sD13q78LRZRgkdAFhXK8SBUAewRNBcPEokTr6oee8DwH50XSlmwQTup15yaLF/QL jERplAwxIl2Em4m59cPukC2CDKPMWM6r4Wi2qsQAas9aVUAg167l7HRENyxrXuzC8XxJHVjPQt5 ScijVWlzpCbn5Sju87xHZdO88I2EjCm+yGpi3rO69v255BNPUvOupMEfYX97honZTk9+WvNmoLl 8V1ynzhVeLchXZJ0EXCtYQ3eMDjW9dE33hKX46XugRwY9JBXzWRj/eJH8mFQ+52MEN11jZPNI5A jqPYcBkgMFzWKhDWyRp9BBJhj9ByM6bSAq1yYXx57b9ily6JqFwheJaxahHzqWxg3i758rzD4Hp ku7/olFYxNi7QYHJxZoc7k2FlDqq/XB/4DsnQb3TJhVEsicuRmrXj+MLFpVXtr10+Bo0keXLXnT hOF67KqwhbI/CpVB2NJMVysMJPJ+1yuNhTPTo2WTIkejSnK6PPxRYI5mrhdpsrAeOJXNyHqn/jY /nNiD3dJSTefahe132zRw27SI5Bv5mag9vX7lI109g9gooec+qymYZuVwg= X-Received: by 2002:a05:6000:46c8:b0:482:552f:ef68 with SMTP id ffacd0b85a97d-482552fef9bmr23788324f8f.19.1786966430915; Mon, 17 Aug 2026 04:33:50 -0700 (PDT) From: Alexander Mikhalitsyn To: qemu-devel@nongnu.org Cc: qemu-arm@nongnu.org, =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Peter Maydell , =?UTF-8?q?St=C3=A9phane=20Graber?= , Paolo Bonzini , Alexander Mikhalitsyn , =?UTF-8?q?Alex=20Benn=C3=A9e?= , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Subject: [PATCH v3] hw/char/pl011: support backend hotswap Date: Mon, 17 Aug 2026 13:33:49 +0200 Message-ID: <20260817113349.103833-1-alexander@mihalicyn.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: pass client-ip=2a00:1450:4864:20::435; envelope-from=alexander@mihalicyn.com; helo=mail-wr1-x435.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @mihalicyn.com) X-ZM-MESSAGEID: 1786966483877158500 From: Alexander Mikhalitsyn Currently, when Incus issues "chardev-change" QMP command to change chardev backend from ringbuf to socket it receives an error (with aarch64 V= M): "Chardev user does not support chardev hotswap" [1], [2] Let's fix this by properly implementing BackendChangeHandler for pl011. Please, note that we have to "replay" CHR_IOCTL_SERIAL_SET_BREAK, because if BRK bit was set before backend change (i.e. (s->lcr & LCR_BRK) is true), then after change we need to send break to a new backend too. Link: https://discuss.linuxcontainers.org/t/unable-to-connect-to-vm-console= -on-arm-architecture/23096/3 [1] Link: https://github.com/lxc/distrobuilder/issues/892 [2] Reported-by: St=C3=A9phane Graber Reviewed-by: Alex Benn=C3=A9e Signed-off-by: Alexander Mikhalitsyn --- v3: - introduced pl011_set_handlers() [ as suggested by Alex Benn=C3=A9e ] - introduced pl011_set_break() [ as suggested by Philippe Mathieu-Daud=C3=A9 ] v2: - fixed a typo in commit author name [ I did `git format-patch` and copied this patch from my Raspberry PI dev/test machine and it turns out that I have a stupid typo in my `git config get user.name` on that machine. ] - added RWB tag from Alex Benn=C3=A9e - adjusted a commit message --- hw/char/pl011.c | 34 +++++++++++++++++++++++++++++----- 1 file changed, 29 insertions(+), 5 deletions(-) diff --git a/hw/char/pl011.c b/hw/char/pl011.c index cb12c3e224f..031afa5b246 100644 --- a/hw/char/pl011.c +++ b/hw/char/pl011.c @@ -425,6 +425,15 @@ static void pl011_loopback_break(PL011State *s, int br= k_enable) } } =20 +static inline int pl011_set_break(PL011State *s, uint64_t lcr) +{ + int break_enable =3D lcr & LCR_BRK; + + qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_BREAK, &break_enable); + + return break_enable; +} + static void pl011_write(void *opaque, hwaddr offset, uint64_t value, unsigned size) { @@ -462,9 +471,7 @@ static void pl011_write(void *opaque, hwaddr offset, pl011_reset_tx_fifo(s); } if ((s->lcr ^ value) & LCR_BRK) { - int break_enable =3D value & LCR_BRK; - qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_BREAK, - &break_enable); + int break_enable =3D pl011_set_break(s, value); pl011_loopback_break(s, break_enable); } s->lcr =3D value; @@ -660,12 +667,29 @@ static void pl011_init(Object *obj) s->id =3D pl011_id_arm; } =20 +static int pl011_be_change(void *opaque); + +static inline void pl011_set_handlers(PL011State *s) +{ + qemu_chr_fe_set_handlers(&s->chr, pl011_can_receive, pl011_receive, + pl011_event, pl011_be_change, s, NULL, true); +} + +static int pl011_be_change(void *opaque) +{ + PL011State *s =3D opaque; + + pl011_set_handlers(s); + pl011_set_break(s, s->lcr); + + return 0; +} + static void pl011_realize(DeviceState *dev, Error **errp) { PL011State *s =3D PL011(dev); =20 - qemu_chr_fe_set_handlers(&s->chr, pl011_can_receive, pl011_receive, - pl011_event, NULL, s, NULL, true); + pl011_set_handlers(s); } =20 static void pl011_reset(DeviceState *dev) --=20 2.47.3