* [PATCH v2] ACPI: SPCR: Support Precise Baud Rate filed
@ 2025-09-12 12:25 cp0613
2025-09-12 14:02 ` Rafael J. Wysocki
2025-09-13 5:24 ` [PATCH v2] " Guo Ren
0 siblings, 2 replies; 8+ messages in thread
From: cp0613 @ 2025-09-12 12:25 UTC (permalink / raw)
To: rafael, lenb, guoren, jeeheng.sia; +Cc: linux-acpi, linux-kernel, Chen Pei
From: Chen Pei <cp0613@linux.alibaba.com>
The Microsoft Serial Port Console Redirection (SPCR) specification
revision 1.09 comprises additional field: Precise Baud Rate [1].
It is used to describe non-traditional baud rates (such as those
used by high-speed UARTs).
It contains a specific non-zero baud rate which overrides the value
of the Configured Baud Rate field. If this field is zero or not
present, Configured Baud Rate is used.
Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table # 1
Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
---
drivers/acpi/spcr.c | 54 ++++++++++++++++++++++++++-------------------
1 file changed, 31 insertions(+), 23 deletions(-)
diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index cd36a97b0ea2..a97b02ee5538 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -146,29 +146,37 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
goto done;
}
- switch (table->baud_rate) {
- case 0:
- /*
- * SPCR 1.04 defines 0 as a preconfigured state of UART.
- * Assume firmware or bootloader configures console correctly.
- */
- baud_rate = 0;
- break;
- case 3:
- baud_rate = 9600;
- break;
- case 4:
- baud_rate = 19200;
- break;
- case 6:
- baud_rate = 57600;
- break;
- case 7:
- baud_rate = 115200;
- break;
- default:
- err = -ENOENT;
- goto done;
+ /*
+ * SPCR 1.09 defines Precise Baud Rate Filed contains a specific
+ * non-zero baud rate which overrides the value of the Configured
+ * Baud Rate field. If this field is zero or not present, Configured
+ * Baud Rate is used.
+ */
+ if (table->precise_baudrate)
+ baud_rate = table->precise_baudrate;
+ else switch (table->baud_rate) {
+ case 0:
+ /*
+ * SPCR 1.04 defines 0 as a preconfigured state of UART.
+ * Assume firmware or bootloader configures console correctly.
+ */
+ baud_rate = 0;
+ break;
+ case 3:
+ baud_rate = 9600;
+ break;
+ case 4:
+ baud_rate = 19200;
+ break;
+ case 6:
+ baud_rate = 57600;
+ break;
+ case 7:
+ baud_rate = 115200;
+ break;
+ default:
+ err = -ENOENT;
+ goto done;
}
/*
--
2.49.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [PATCH v2] ACPI: SPCR: Support Precise Baud Rate filed
2025-09-12 12:25 [PATCH v2] ACPI: SPCR: Support Precise Baud Rate filed cp0613
@ 2025-09-12 14:02 ` Rafael J. Wysocki
2025-09-13 7:07 ` [PATCH] " cp0613
2025-09-13 5:24 ` [PATCH v2] " Guo Ren
1 sibling, 1 reply; 8+ messages in thread
From: Rafael J. Wysocki @ 2025-09-12 14:02 UTC (permalink / raw)
To: cp0613; +Cc: rafael, lenb, guoren, jeeheng.sia, linux-acpi, linux-kernel
On Fri, Sep 12, 2025 at 2:25 PM <cp0613@linux.alibaba.com> wrote:
>
> From: Chen Pei <cp0613@linux.alibaba.com>
>
> The Microsoft Serial Port Console Redirection (SPCR) specification
> revision 1.09 comprises additional field: Precise Baud Rate [1].
>
> It is used to describe non-traditional baud rates (such as those
> used by high-speed UARTs).
>
> It contains a specific non-zero baud rate which overrides the value
> of the Configured Baud Rate field. If this field is zero or not
> present, Configured Baud Rate is used.
>
> Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table # 1
>
> Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
> ---
> drivers/acpi/spcr.c | 54 ++++++++++++++++++++++++++-------------------
> 1 file changed, 31 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
> index cd36a97b0ea2..a97b02ee5538 100644
> --- a/drivers/acpi/spcr.c
> +++ b/drivers/acpi/spcr.c
> @@ -146,29 +146,37 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
> goto done;
> }
>
> - switch (table->baud_rate) {
> - case 0:
> - /*
> - * SPCR 1.04 defines 0 as a preconfigured state of UART.
> - * Assume firmware or bootloader configures console correctly.
> - */
> - baud_rate = 0;
> - break;
> - case 3:
> - baud_rate = 9600;
> - break;
> - case 4:
> - baud_rate = 19200;
> - break;
> - case 6:
> - baud_rate = 57600;
> - break;
> - case 7:
> - baud_rate = 115200;
> - break;
> - default:
> - err = -ENOENT;
> - goto done;
> + /*
> + * SPCR 1.09 defines Precise Baud Rate Filed contains a specific
> + * non-zero baud rate which overrides the value of the Configured
> + * Baud Rate field. If this field is zero or not present, Configured
> + * Baud Rate is used.
> + */
> + if (table->precise_baudrate)
> + baud_rate = table->precise_baudrate;
> + else switch (table->baud_rate) {
Please do not change the indentation below.
> + case 0:
> + /*
> + * SPCR 1.04 defines 0 as a preconfigured state of UART.
> + * Assume firmware or bootloader configures console correctly.
> + */
> + baud_rate = 0;
> + break;
> + case 3:
> + baud_rate = 9600;
> + break;
> + case 4:
> + baud_rate = 19200;
> + break;
> + case 6:
> + baud_rate = 57600;
> + break;
> + case 7:
> + baud_rate = 115200;
> + break;
> + default:
> + err = -ENOENT;
> + goto done;
> }
>
> /*
> --
> 2.49.0
>
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] ACPI: SPCR: Support Precise Baud Rate filed
2025-09-12 14:02 ` Rafael J. Wysocki
@ 2025-09-13 7:07 ` cp0613
0 siblings, 0 replies; 8+ messages in thread
From: cp0613 @ 2025-09-13 7:07 UTC (permalink / raw)
To: rafael; +Cc: cp0613, guoren, jeeheng.sia, lenb, linux-acpi, linux-kernel
On Fri, 12 Sep 2025 16:02:58 +0200, rafael@kernel.org wrote:
> > + if (table->precise_baudrate)
> > + baud_rate = table->precise_baudrate;
> > + else switch (table->baud_rate) {>
> Please do not change the indentation below.>
> > + case 0:
> > + /*
> > + * SPCR 1.04 defines 0 as a preconfigured state of UART.
> > + * Assume firmware or bootloader configures console correctly.
> > + */
> > + baud_rate = 0;
> > + break;
I got it.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2] ACPI: SPCR: Support Precise Baud Rate filed
2025-09-12 12:25 [PATCH v2] ACPI: SPCR: Support Precise Baud Rate filed cp0613
2025-09-12 14:02 ` Rafael J. Wysocki
@ 2025-09-13 5:24 ` Guo Ren
2025-09-13 7:06 ` [PATCH] " cp0613
1 sibling, 1 reply; 8+ messages in thread
From: Guo Ren @ 2025-09-13 5:24 UTC (permalink / raw)
To: cp0613; +Cc: rafael, lenb, jeeheng.sia, linux-acpi, linux-kernel
On Fri, Sep 12, 2025 at 8:25 PM <cp0613@linux.alibaba.com> wrote:
>
> From: Chen Pei <cp0613@linux.alibaba.com>
>
> The Microsoft Serial Port Console Redirection (SPCR) specification
> revision 1.09 comprises additional field: Precise Baud Rate [1].
>
> It is used to describe non-traditional baud rates (such as those
> used by high-speed UARTs).
>
> It contains a specific non-zero baud rate which overrides the value
> of the Configured Baud Rate field. If this field is zero or not
The spec states that it would "override" the baud rate. That means it
should happen behind the table->baud_rate or firmware still needs to
give out a legal Configured Baud Rate for precise_baudrate.
Then, we move these:
+ if (table->precise_baudrate)
+ baud_rate = table->precise_baudrate;
behind the "switch (table->baud_rate) {}".
Right?
> present, Configured Baud Rate is used.
>
> Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table # 1
>
> Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
> ---
> drivers/acpi/spcr.c | 54 ++++++++++++++++++++++++++-------------------
> 1 file changed, 31 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
> index cd36a97b0ea2..a97b02ee5538 100644
> --- a/drivers/acpi/spcr.c
> +++ b/drivers/acpi/spcr.c
> @@ -146,29 +146,37 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
> goto done;
> }
>
> - switch (table->baud_rate) {
> - case 0:
> - /*
> - * SPCR 1.04 defines 0 as a preconfigured state of UART.
> - * Assume firmware or bootloader configures console correctly.
> - */
> - baud_rate = 0;
> - break;
> - case 3:
> - baud_rate = 9600;
> - break;
> - case 4:
> - baud_rate = 19200;
> - break;
> - case 6:
> - baud_rate = 57600;
> - break;
> - case 7:
> - baud_rate = 115200;
> - break;
> - default:
> - err = -ENOENT;
> - goto done;
> + /*
> + * SPCR 1.09 defines Precise Baud Rate Filed contains a specific
> + * non-zero baud rate which overrides the value of the Configured
> + * Baud Rate field. If this field is zero or not present, Configured
> + * Baud Rate is used.
> + */
> + if (table->precise_baudrate)
> + baud_rate = table->precise_baudrate;
> + else switch (table->baud_rate) {
> + case 0:
> + /*
> + * SPCR 1.04 defines 0 as a preconfigured state of UART.
> + * Assume firmware or bootloader configures console correctly.
> + */
> + baud_rate = 0;
> + break;
> + case 3:
> + baud_rate = 9600;
> + break;
> + case 4:
> + baud_rate = 19200;
> + break;
> + case 6:
> + baud_rate = 57600;
> + break;
> + case 7:
> + baud_rate = 115200;
> + break;
> + default:
> + err = -ENOENT;
> + goto done;
> }
>
> /*
> --
> 2.49.0
>
--
Best Regards
Guo Ren
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] ACPI: SPCR: Support Precise Baud Rate filed
2025-09-13 5:24 ` [PATCH v2] " Guo Ren
@ 2025-09-13 7:06 ` cp0613
0 siblings, 0 replies; 8+ messages in thread
From: cp0613 @ 2025-09-13 7:06 UTC (permalink / raw)
To: guoren; +Cc: cp0613, jeeheng.sia, lenb, linux-acpi, linux-kernel, rafael
On Sat, 13 Sep 2025 13:24:21 +0800, guoren@kernel.org wrote:
> > It contains a specific non-zero baud rate which overrides the value
> > of the Configured Baud Rate field. If this field is zero or not
> The spec states that it would "override" the baud rate. That means it
> should happen behind the table->baud_rate or firmware still needs to
> give out a legal Configured Baud Rate for precise_baudrate.>
> Then, we move these:
> + if (table->precise_baudrate)
> + baud_rate = table->precise_baudrate;
> behind the "switch (table->baud_rate) {}".>
> Right?>
> > present, Configured Baud Rate is used.
OK, I think "override" means priority in a sense, there is no need to do
an overriding action in the behavior.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH] ACPI: SPCR: Support Precise Baud Rate filed
@ 2025-09-12 8:57 cp0613
2025-09-12 9:29 ` Rafael J. Wysocki
0 siblings, 1 reply; 8+ messages in thread
From: cp0613 @ 2025-09-12 8:57 UTC (permalink / raw)
To: rafael, lenb, guoren, jeeheng.sia; +Cc: linux-acpi, linux-kernel, Chen Pei
From: Chen Pei <cp0613@linux.alibaba.com>
The Microsoft Serial Port Console Redirection (SPCR) specification
revision 1.09 comprises additional field: Precise Baud Rate [1].
It is used to describe non-traditional baud rates (such as those
used by high-speed UARTs).
It contains a specific non-zero baud rate which overrides the value
of the Configured Baud Rate field. If this field is zero or not
present, Configured Baud Rate is used.
Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table # 1
Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
---
drivers/acpi/spcr.c | 56 ++++++++++++++++++++++++++-------------------
1 file changed, 33 insertions(+), 23 deletions(-)
diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index cd36a97b0ea2..69142c2ac4b3 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -146,29 +146,39 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
goto done;
}
- switch (table->baud_rate) {
- case 0:
- /*
- * SPCR 1.04 defines 0 as a preconfigured state of UART.
- * Assume firmware or bootloader configures console correctly.
- */
- baud_rate = 0;
- break;
- case 3:
- baud_rate = 9600;
- break;
- case 4:
- baud_rate = 19200;
- break;
- case 6:
- baud_rate = 57600;
- break;
- case 7:
- baud_rate = 115200;
- break;
- default:
- err = -ENOENT;
- goto done;
+ /*
+ * SPCR 1.09 defines Precise Baud Rate Filed contains a specific
+ * non-zero baud rate which overrides the value of the Configured
+ * Baud Rate field. If this field is zero or not present, Configured
+ * Baud Rate is used.
+ */
+ if (table->precise_baudrate)
+ baud_rate = table->precise_baudrate;
+ else {
+ switch (table->baud_rate) {
+ case 0:
+ /*
+ * SPCR 1.04 defines 0 as a preconfigured state of UART.
+ * Assume firmware or bootloader configures console correctly.
+ */
+ baud_rate = 0;
+ break;
+ case 3:
+ baud_rate = 9600;
+ break;
+ case 4:
+ baud_rate = 19200;
+ break;
+ case 6:
+ baud_rate = 57600;
+ break;
+ case 7:
+ baud_rate = 115200;
+ break;
+ default:
+ err = -ENOENT;
+ goto done;
+ }
}
/*
--
2.49.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [PATCH] ACPI: SPCR: Support Precise Baud Rate filed
2025-09-12 8:57 cp0613
@ 2025-09-12 9:29 ` Rafael J. Wysocki
2025-09-12 12:23 ` cp0613
0 siblings, 1 reply; 8+ messages in thread
From: Rafael J. Wysocki @ 2025-09-12 9:29 UTC (permalink / raw)
To: cp0613; +Cc: rafael, lenb, guoren, jeeheng.sia, linux-acpi, linux-kernel
On Fri, Sep 12, 2025 at 10:58 AM <cp0613@linux.alibaba.com> wrote:
>
> From: Chen Pei <cp0613@linux.alibaba.com>
>
> The Microsoft Serial Port Console Redirection (SPCR) specification
> revision 1.09 comprises additional field: Precise Baud Rate [1].
>
> It is used to describe non-traditional baud rates (such as those
> used by high-speed UARTs).
>
> It contains a specific non-zero baud rate which overrides the value
> of the Configured Baud Rate field. If this field is zero or not
> present, Configured Baud Rate is used.
>
> Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table # 1
>
> Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
> ---
> drivers/acpi/spcr.c | 56 ++++++++++++++++++++++++++-------------------
> 1 file changed, 33 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
> index cd36a97b0ea2..69142c2ac4b3 100644
> --- a/drivers/acpi/spcr.c
> +++ b/drivers/acpi/spcr.c
> @@ -146,29 +146,39 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
> goto done;
> }
>
> - switch (table->baud_rate) {
> - case 0:
> - /*
> - * SPCR 1.04 defines 0 as a preconfigured state of UART.
> - * Assume firmware or bootloader configures console correctly.
> - */
> - baud_rate = 0;
> - break;
> - case 3:
> - baud_rate = 9600;
> - break;
> - case 4:
> - baud_rate = 19200;
> - break;
> - case 6:
> - baud_rate = 57600;
> - break;
> - case 7:
> - baud_rate = 115200;
> - break;
> - default:
> - err = -ENOENT;
> - goto done;
> + /*
> + * SPCR 1.09 defines Precise Baud Rate Filed contains a specific
> + * non-zero baud rate which overrides the value of the Configured
> + * Baud Rate field. If this field is zero or not present, Configured
> + * Baud Rate is used.
> + */
> + if (table->precise_baudrate)
> + baud_rate = table->precise_baudrate;
> + else {
The outer braces here are redundant and if you combined the "else"
above with the "switch ()" statement below in one line, the patch
would be smaller.
> + switch (table->baud_rate) {
> + case 0:
> + /*
> + * SPCR 1.04 defines 0 as a preconfigured state of UART.
> + * Assume firmware or bootloader configures console correctly.
> + */
> + baud_rate = 0;
> + break;
> + case 3:
> + baud_rate = 9600;
> + break;
> + case 4:
> + baud_rate = 19200;
> + break;
> + case 6:
> + baud_rate = 57600;
> + break;
> + case 7:
> + baud_rate = 115200;
> + break;
> + default:
> + err = -ENOENT;
> + goto done;
> + }
> }
>
> /*
> --
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] ACPI: SPCR: Support Precise Baud Rate filed
2025-09-12 9:29 ` Rafael J. Wysocki
@ 2025-09-12 12:23 ` cp0613
0 siblings, 0 replies; 8+ messages in thread
From: cp0613 @ 2025-09-12 12:23 UTC (permalink / raw)
To: rafael; +Cc: cp0613, guoren, jeeheng.sia, lenb, linux-acpi, linux-kernel
On Fri, 12 Sep 2025 11:29:44 +0200, rafael@kernel.org wrote:
> > + if (table->precise_baudrate)
> > + baud_rate =3D table->precise_baudrate;
> > + else {>
> The outer braces here are redundant and if you combined the "else"
> above with the "switch ()" statement below in one line, the patch
> would be smaller.>
> > + switch (table->baud_rate) {
> > + case 0:
Thanks for your suggestion. I will modify it.
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2025-09-13 7:07 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
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2025-09-12 12:25 [PATCH v2] ACPI: SPCR: Support Precise Baud Rate filed cp0613
2025-09-12 14:02 ` Rafael J. Wysocki
2025-09-13 7:07 ` [PATCH] " cp0613
2025-09-13 5:24 ` [PATCH v2] " Guo Ren
2025-09-13 7:06 ` [PATCH] " cp0613
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2025-09-12 8:57 cp0613
2025-09-12 9:29 ` Rafael J. Wysocki
2025-09-12 12:23 ` cp0613
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