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[80.230.79.166]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43796a5d156sm61280027f8f.5.2026.02.20.06.50.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Feb 2026 06:51:00 -0800 (PST) Date: Fri, 20 Feb 2026 09:50:57 -0500 From: "Michael S. Tsirkin" To: Li Chen Cc: qemu-devel@nongnu.org, qemu-arm@nongnu.org, qemu-riscv@nongnu.org, Igor Mammedov , Ani Sinha , Peter Maydell , Shannon Zhao , Song Gao , Bibo Mao , Jiaxun Yang , Sunil V L , Palmer Dabbelt , Alistair Francis , Weiwei Li , Daniel Henrique Barboza , Liu Zhiwei , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Subject: Re: [PATCH v7 1/1] acpi/virt: suppress SPCR when UART0 has no serial backend Message-ID: <20260220094834-mutt-send-email-mst@kernel.org> References: <20260219130403.810220-1-me@linux.beauty> MIME-Version: 1.0 In-Reply-To: <20260219130403.810220-1-me@linux.beauty> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 8nXD2fuUWvjH1X_Fg8xJKJCeazujvlhn2haWsZZA0Fc_1771599062 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.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, DKIMWL_WL_HIGH=-0.049, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On Thu, Feb 19, 2026 at 09:04:02PM +0800, Li Chen wrote: > From: Li Chen > > virt machines always instantiate a PL011/16550 UART at slot 0 and describe > it in ACPI (DSDT and optional SPCR table). When the command line disables > the serial backend (e.g. "-serial none"), SPCR still points at UART0 and > the guest may pick it as the preferred console even though it is not > usable. > > Only generate SPCR when UART0 has a chardev backend attached. Keep the > UART device description in DSDT unchanged so the guest-visible UART > topology does not change. > > The bios-tables-test qtests use "-serial null" to keep SPCR enabled while > discarding firmware serial output, avoiding TAP stdout corruption. > > Suggested-by: Philippe Mathieu-Daudé > Signed-off-by: Li Chen > Reviewed-by: Sunil V L > --- So -serial null gives a device -serial none hides it from guest. Sensible. And yet, out of abundance of caution, maybe keep the legacy behaviour for existing machine types. No? > v6 -> v7: > Do not gate DSDT UART devices on serial_hd(0); only gate SPCR. > Drop the serial_exists() helper added by v6. > Keep bios-tables-test using "-serial null" (comment wording update). > > v5 -> v6: > Fix TAP parsing errors by using "-serial null" in bios-tables-test. > > v4 -> v5: > Also suppress UART device & SPCR when guest has no serial hardware on > loongarch. > Rename serial_exist to serial_exists. > Fix style issues. > > hw/arm/virt-acpi-build.c | 3 ++- > hw/loongarch/virt-acpi-build.c | 2 +- > hw/riscv/virt-acpi-build.c | 3 ++- > tests/qtest/bios-tables-test.c | 7 +++++-- > 4 files changed, 10 insertions(+), 5 deletions(-) > > diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c > index c145678185..1411f98ea1 100644 > --- a/hw/arm/virt-acpi-build.c > +++ b/hw/arm/virt-acpi-build.c > @@ -64,6 +64,7 @@ > #include "hw/virtio/virtio-acpi.h" > #include "target/arm/cpu.h" > #include "target/arm/multiprocessing.h" > +#include "system/system.h" > > #define ARM_SPI_BASE 32 > > @@ -1291,7 +1292,7 @@ void virt_acpi_build(VirtMachineState *vms, AcpiBuildTables *tables) > > acpi_add_table(table_offsets, tables_blob); > > - if (ms->acpi_spcr_enabled) { > + if (ms->acpi_spcr_enabled && serial_hd(0)) { > spcr_setup(tables_blob, tables->linker, vms); > } > > diff --git a/hw/loongarch/virt-acpi-build.c b/hw/loongarch/virt-acpi-build.c > index 54ac94e17d..dc8bbb9fdc 100644 > --- a/hw/loongarch/virt-acpi-build.c > +++ b/hw/loongarch/virt-acpi-build.c > @@ -546,7 +546,7 @@ static void acpi_build(AcpiBuildTables *tables, MachineState *machine) > build_srat(tables_blob, tables->linker, machine); > acpi_add_table(table_offsets, tables_blob); > > - if (machine->acpi_spcr_enabled) > + if (machine->acpi_spcr_enabled && serial_hd(0)) > spcr_setup(tables_blob, tables->linker, machine); > > if (machine->numa_state->num_nodes) { > diff --git a/hw/riscv/virt-acpi-build.c b/hw/riscv/virt-acpi-build.c > index f1406cb683..29080d1125 100644 > --- a/hw/riscv/virt-acpi-build.c > +++ b/hw/riscv/virt-acpi-build.c > @@ -39,6 +39,7 @@ > #include "qapi/error.h" > #include "qemu/error-report.h" > #include "system/reset.h" > +#include "system/system.h" > > #define ACPI_BUILD_TABLE_SIZE 0x20000 > #define ACPI_BUILD_INTC_ID(socket, index) ((socket << 24) | (index)) > @@ -890,7 +891,7 @@ static void virt_acpi_build(RISCVVirtState *s, AcpiBuildTables *tables) > > acpi_add_table(table_offsets, tables_blob); > > - if (ms->acpi_spcr_enabled) { > + if (ms->acpi_spcr_enabled && serial_hd(0)) { > spcr_setup(tables_blob, tables->linker, s); > } > > diff --git a/tests/qtest/bios-tables-test.c b/tests/qtest/bios-tables-test.c > index e489d94331..37f2b72d83 100644 > --- a/tests/qtest/bios-tables-test.c > +++ b/tests/qtest/bios-tables-test.c > @@ -825,10 +825,13 @@ static char *test_acpi_create_args(test_data *data, const char *params) > /* > * TODO: convert '-drive if=pflash' to new syntax (see e33763be7cd3) > * when arm/virt boad starts to support it. > + * NOTE: Explicitly add "-serial null" to keep SPCR enabled while > + * discarding firmware serial output (avoid corrupting TAP > + * stdout). > */ > if (data->cd) { > args = g_strdup_printf("-machine %s%s %s -accel tcg " > - "-nodefaults -nographic " > + "-nodefaults -serial null -nographic " > "-drive if=pflash,format=raw,file=%s,readonly=on " > "-drive if=pflash,format=raw,file=%s,snapshot=on -cdrom %s %s", > data->machine, data->machine_param ?: "", > @@ -836,7 +839,7 @@ static char *test_acpi_create_args(test_data *data, const char *params) > data->uefi_fl1, data->uefi_fl2, data->cd, params ? params : ""); > } else { > args = g_strdup_printf("-machine %s%s %s -accel tcg " > - "-nodefaults -nographic " > + "-nodefaults -serial null -nographic " > "-drive if=pflash,format=raw,file=%s,readonly=on " > "-drive if=pflash,format=raw,file=%s,snapshot=on %s", > data->machine, data->machine_param ?: "", > -- > 2.52.0