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[2003:cf:573b:e100:f155:5239:60c6:bbe7]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c2459223816sm459070266b.57.2026.08.21.03.48.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Aug 2026 03:48:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mihalicyn.com; s=mihalicyn; t=1787309314; x=1787914114; 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=F+0CD52geVbAnj+JLHfj3iZ7QCvQAELc6Kfran7U1FM=; b=Atc3wTth7kAIqEOpzBbLsbftFuxt8CFcKcy5l+ZAyHtGlVYyJD4UDuHn3KkITU1WdR RJMRqphRqNg2FbKAkWY7FyLH5Ke1TrZFBg0HfXe03bh2p7euiI40GpryVt1nDbls2ab2 DSHJvzP9b2xwFjrEFyfVZJ0a2t9gkV5dzgrIk= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787309314; x=1787914114; 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=F+0CD52geVbAnj+JLHfj3iZ7QCvQAELc6Kfran7U1FM=; b=ZJUIqpUvYopUayXJj4fv01UQCe/GiNGFxiukDMBd5UqF2KYZYugCrWJWGpk+cugSKH LR9aglTf7YF5nKbF0muksgxbYtKHeHXxDMEc0TlrbQpBLwwftTZdiD6gwm7RP+EBkHXN OSWkCdxR6dCeVuxKUf8gd4iTwqtOc9X0wAw3h06GczMZzfIywEiFWQhIullGfHVeeYt1 G+nZtYISCAYpMUXByIqp3ndP7sYPnFVAh2rl4b5bDMi+GSGESvkLYJNUU8XCMnSpfsVa d8xp8xvRu9cYrD1mWOxGhmbQ6mKvM53TRJhvhc4t6iojQlCgnUNbgX400Haqj0wBuDGo U2MQ== X-Gm-Message-State: AFuF++kQr6ufdvUSGIP7mytVS/MPQ14cK0ZB4/U5M/KVf8UBTgo0zbEG wO6m9B5Jxg4roHFCH75PGhIkNFSOz6gOavrOKI+uTXaPSLx79n2HkO6+b0a6ls5K23QsM7AcDMF ZoeFg X-Gm-Gg: AR+sD12ZGKPd41T00wzqsj8btRW+aOvBi63gK0ZOmjTBg83FeZtHZnAe9LZzvR8Wlrj oEsE6/Ed3VNXtsLZ4jQGcDAZRMOwuKk4RFqhqfej+qrEd4Oifjk4a+67hwkx4icHIR81GrzBMdK V6d5yzLRRKFfP+IKYRLib4H/4Osy4IcwZH+MYGgFyhfGpMm2YRncjcZTfwVM+jhewowJJlr1AjX lCC8miTNHx+fmWVU8O/LZRxY/Aw2ay4ToWmHIjoPIkdTEmVVN6DC8ppswl3Fj2Ch/UMrBEYMIKY oWh2415GNTbB9dk/W2pmdu0C6rMY/V7nqqdQ6efZUG1JPX3yl2XbRWS+wVi6p6GNN1e5YImNPNh thNJIjHIU2xsAzWJByYb4WuaGuWdLe4Mh0EKFmXz7v9OmiM2Usbl8uwOlUn9lJWhBoLw5bMZyhX F1tmUzWg4uB+6fwByljeb99iSX1ZZgpgNBDFr8Bg3CLrjonkszXx7pwx5chx9djO3Vxmnu1IpoJ qvuvml9BZcWex8aAoDq8bC9I5K4fR0buJnYuGi27i1FxpU+3LA24+mSxmI= X-Received: by 2002:a17:907:d649:b0:c19:6d4a:425b with SMTP id a640c23a62f3a-c246a626403mr490436766b.18.1787309314396; Fri, 21 Aug 2026 03:48:34 -0700 (PDT) From: Alexander Mikhalitsyn To: qemu-devel@nongnu.org Cc: Peter Maydell , Alexander Mikhalitsyn , qemu-arm@nongnu.org, =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Paolo Bonzini , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , =?UTF-8?q?St=C3=A9phane=20Graber?= , =?UTF-8?q?Alex=20Benn=C3=A9e?= Subject: [PATCH v4] hw/char/pl011: support backend hotswap Date: Fri, 21 Aug 2026 12:48:32 +0200 Message-ID: <20260821104832.151452-1-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::52c; envelope-from=alexander@mihalicyn.com; helo=mail-ed1-x52c.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=ham 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: 1787309354492158500 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 --- v4: - changed pl011_set_break() signature [ as suggested by Peter Maydell ] 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 | 31 ++++++++++++++++++++++++++----- 1 file changed, 26 insertions(+), 5 deletions(-) diff --git a/hw/char/pl011.c b/hw/char/pl011.c index cb12c3e224f..5ad9e7358d5 100644 --- a/hw/char/pl011.c +++ b/hw/char/pl011.c @@ -425,6 +425,11 @@ static void pl011_loopback_break(PL011State *s, int br= k_enable) } } =20 +static inline void pl011_set_break(PL011State *s, int brk_enable) +{ + qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_BREAK, &brk_enable); +} + static void pl011_write(void *opaque, hwaddr offset, uint64_t value, unsigned size) { @@ -462,9 +467,8 @@ 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); + bool break_enable =3D value & LCR_BRK; + pl011_set_break(s, break_enable); pl011_loopback_break(s, break_enable); } s->lcr =3D value; @@ -660,12 +664,29 @@ 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 & LCR_BRK); + + 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