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Message-ID: <56F15D40.9020401@hurleysoftware.com>
Date: Tue, 22 Mar 2016 07:57:04 -0700
From: Peter Hurley <peter@...leysoftware.com>
To: Yury Norov <ynorov@...iumnetworks.com>,
Aleksey Makarov <aleksey.makarov@...aro.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J . Wysocki" <rjw@...ysocki.net>,
Len Brown <lenb@...nel.org>, linux-serial@...r.kernel.org,
linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
Russell King <linux@....linux.org.uk>,
Leif Lindholm <leif.lindholm@...aro.org>,
Graeme Gregory <graeme.gregory@...aro.org>,
Al Stone <ahs3@...hat.com>,
Christopher Covington <cov@...eaurora.org>,
"Zheng, Lv" <lv.zheng@...el.com>, Jiri Slaby <jslaby@...e.com>
Subject: Re: [PATCH v5 3/6] ACPI: parse SPCR and enable matching console
On 03/22/2016 05:26 AM, Yury Norov wrote:
> On Tue, Mar 22, 2016 at 01:46:30PM +0300, Aleksey Makarov wrote:
>> 'ARM Server Base Boot Requiremets' [1] mentions SPCR (Serial Port
>> Console Redirection Table) [2] as a mandatory ACPI table that
>> specifies the configuration of serial console.
>>
>> Parse this table, setup earlycon and enable the specified console.
>>
>> Thanks to Peter Hurley for explaining how this should work.
>>
>> [1] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0044a/index.html
>> [2] https://msdn.microsoft.com/en-us/library/windows/hardware/dn639132(v=vs.85).aspx
>>
>> Signed-off-by: Aleksey Makarov <aleksey.makarov@...aro.org>
>> ---
>> drivers/acpi/Kconfig | 3 ++
>> drivers/acpi/Makefile | 1 +
>> drivers/acpi/spcr.c | 102 ++++++++++++++++++++++++++++++++++++++++++
>> drivers/tty/serial/earlycon.c | 13 ++++--
>> include/linux/acpi.h | 8 ++++
>> 5 files changed, 123 insertions(+), 4 deletions(-)
>> create mode 100644 drivers/acpi/spcr.c
>>
>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>> index 65fb483..5611eb6 100644
>> --- a/drivers/acpi/Kconfig
>> +++ b/drivers/acpi/Kconfig
>> @@ -77,6 +77,9 @@ config ACPI_DEBUGGER_USER
>>
>> endif
>>
>> +config ACPI_SPCR_TABLE
>> + bool
>> +
>> config ACPI_SLEEP
>> bool
>> depends on SUSPEND || HIBERNATION
>> diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
>> index 7395928..f70ae14 100644
>> --- a/drivers/acpi/Makefile
>> +++ b/drivers/acpi/Makefile
>> @@ -82,6 +82,7 @@ obj-$(CONFIG_ACPI_EC_DEBUGFS) += ec_sys.o
>> obj-$(CONFIG_ACPI_CUSTOM_METHOD)+= custom_method.o
>> obj-$(CONFIG_ACPI_BGRT) += bgrt.o
>> obj-$(CONFIG_ACPI_CPPC_LIB) += cppc_acpi.o
>> +obj-$(CONFIG_ACPI_SPCR_TABLE) += spcr.o
>> obj-$(CONFIG_ACPI_DEBUGGER_USER) += acpi_dbg.o
>>
>> # processor has its own "processor." module_param namespace
>> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
>> new file mode 100644
>> index 0000000..1ec82f9
>> --- /dev/null
>> +++ b/drivers/acpi/spcr.c
>> @@ -0,0 +1,102 @@
>> +/*
>> + * Copyright (c) 2012, Intel Corporation
>> + * Copyright (c) 2015, Red Hat, Inc.
>> + * Copyright (c) 2015, 2016 Linaro Ltd.
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + *
>> + */
>> +
>> +#define pr_fmt(fmt) "ACPI: SPCR: " fmt
>> +
>> +#include <linux/acpi.h>
>> +#include <linux/console.h>
>> +#include <linux/kernel.h>
>> +#include <linux/serial_core.h>
>> +
>> +static bool init_earlycon;
>> +
>> +void __init init_spcr_earlycon(void)
>> +{
>> + init_earlycon = true;
>> +}
>> +
>
> 1. I see you keep in mind multiple access.
Concurrent access is not a concern here: only the boot cpu is running
and intrs are off.
The "init_earlycon" flag is used because parsing the "earlycon" early param
is earlier than parsing ACPI tables.
Then you'd worry about race
> conditions as well. In this case, I'd consider atomic access to
> variable.
> 2. It seems you need is_init() helper too.
>
>> +int __init parse_spcr(void)
>> +{
>> + static char opts[64];
>> + struct acpi_table_spcr *table;
>> + acpi_size table_size;
>> + acpi_status status;
>> + char *uart;
>> + char *iotype;
>> + int baud_rate;
>> + int err = 0;
>
> You can do not initialize 'err'.
Why?
>
>> +
>> + status = acpi_get_table_with_size(ACPI_SIG_SPCR, 0,
>> + (struct acpi_table_header **)&table,
>> + &table_size);
>> +
>> + if (ACPI_FAILURE(status))
>> + return -ENOENT;
>> +
>> + if (table->header.revision < 2) {
>> + err = -EINVAL;
>> + pr_err("wrong table version\n");
>> + goto done;
>> + }
>> +
>> + iotype = (table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) ?
>> + "mmio" : "io";
>> +
>> + switch (table->interface_type) {
>> + case ACPI_DBG2_ARM_SBSA_32BIT:
>> + iotype = "mmio32";
>> + /* fall through */
>> + case ACPI_DBG2_ARM_PL011:
>> + case ACPI_DBG2_ARM_SBSA_GENERIC:
>> + case ACPI_DBG2_BCM2835:
>> + uart = "pl011";
>> + break;
>> + case ACPI_DBG2_16550_COMPATIBLE:
>> + case ACPI_DBG2_16550_SUBSET:
>> + uart = "uart";
>> + break;
>> + default:
>> + err = -ENOENT;
>> + goto done;
>> + }
>> +
>> + switch (table->baud_rate) {
>> + 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;
>> + }
>> +
>> + sprintf(opts, "%s,%s,0x%llx,%d", uart, iotype,
>> + table->serial_port.address, baud_rate);
>
> As 'opts' is static, don't you need to take some measures to prevent
> concurrent access. The simpler measure for me is to declare it on
> stack.
Again, concurrent access is not a concern at this early time.
Regards,
Peter Hurley
>> +
>> + pr_info("console: %s", opts);
>> +
>> + if (init_earlycon)
>> + setup_earlycon(opts);
>> +
>> + err = add_preferred_console(uart, 0, opts + strlen(uart) + 1);
>> +
>> +done:
>> + early_acpi_os_unmap_memory((void __iomem *)table, table_size);
>> + return err;
>> +}
>> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
>> index d217366..ec030c9 100644
>> --- a/drivers/tty/serial/earlycon.c
>> +++ b/drivers/tty/serial/earlycon.c
>> @@ -22,6 +22,7 @@
>> #include <linux/sizes.h>
>> #include <linux/of.h>
>> #include <linux/of_fdt.h>
>> +#include <linux/acpi.h>
>>
>> #ifdef CONFIG_FIX_EARLYCON_MEM
>> #include <asm/fixmap.h>
>> @@ -206,11 +207,15 @@ static int __init param_setup_earlycon(char *buf)
>> int err;
>>
>> /*
>> - * Just 'earlycon' is a valid param for devicetree earlycons;
>> - * don't generate a warning from parse_early_params() in that case
>> + * Just 'earlycon' is a valid param for devicetree and ACPI SPCR
>> + * earlycons; don't generate a warning from parse_early_params()
>> + * in that case
>> */
>> - if (!buf || !buf[0])
>> - return early_init_dt_scan_chosen_serial();
>> + if (!buf || !buf[0]) {
>> + init_spcr_earlycon();
>> + early_init_dt_scan_chosen_serial();
>> + return 0;
>> + }
>>
>> err = setup_earlycon(buf);
>> if (err == -ENOENT || err == -EALREADY)
>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>> index 06ed7e5..ebbb212 100644
>> --- a/include/linux/acpi.h
>> +++ b/include/linux/acpi.h
>> @@ -1004,4 +1004,12 @@ static inline struct fwnode_handle *acpi_get_next_subnode(struct device *dev,
>> #define acpi_probe_device_table(t) ({ int __r = 0; __r;})
>> #endif
>>
>> +#ifdef CONFIG_ACPI_SPCR_TABLE
>> +int parse_spcr(void);
>> +void init_spcr_earlycon(void);
>> +#else
>> +static inline int parse_spcr(void) { return 0; }
>> +static inline void init_spcr_earlycon(void) {}
>> +#endif
>> +
>> #endif /*_LINUX_ACPI_H*/
>> --
>> 2.7.4
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