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Date:   Fri, 22 Oct 2021 16:54:49 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        bp@...en8.de, james.morse@....com, lenb@...nel.org,
        rjw@...ysocki.net, zhangliguang@...ux.alibaba.com,
        zhuo.song@...ux.alibaba.com
Subject: Re: [PATCH v2] ACPI, APEI, EINJ: Relax platform response timeout to
 1 second.

On Fri, Oct 22, 2021 at 09:44:24PM +0800, Shuai Xue wrote:
> When injecting an error into the platform, the OSPM executes an
> EXECUTE_OPERATION action to instruct the platform to begin the injection
> operation. And then, the OSPM busy waits for a while by continually
> executing CHECK_BUSY_STATUS action until the platform indicates that the
> operation is complete. More specifically, the platform is limited to
> respond within 1 millisecond right now. This is too strict for some
> platforms.
> 
> For example, in Arm platform, when injecting a Processor Correctable error,
> the OSPM will warn:
>     Firmware does not respond in time.
> 
> And a message is printed on the console:
>     echo: write error: Input/output error
> 
> We observe that the waiting time for DDR error injection is about 10 ms
> and that for PCIe error injection is about 500 ms in Arm platform.
> 
> In this patch, we relax the response timeout to 1 second and allow user to
> pass the time out value as a argument.
> 
> Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>
> ---
> Changelog v1 -> v2:
> - Implemented the timeout in msleep instead of udelay.
> - Link to the v1 patch: https://lkml.org/lkml/2021/10/14/1402
> ---
>  drivers/acpi/apei/einj.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/acpi/apei/einj.c b/drivers/acpi/apei/einj.c
> index 133156759551..e411eb30e0ee 100644
> --- a/drivers/acpi/apei/einj.c
> +++ b/drivers/acpi/apei/einj.c
> @@ -28,9 +28,9 @@
>  #undef pr_fmt
>  #define pr_fmt(fmt) "EINJ: " fmt
>  
> -#define SPIN_UNIT		100			/* 100ns */
> -/* Firmware should respond within 1 milliseconds */
> -#define FIRMWARE_TIMEOUT	(1 * NSEC_PER_MSEC)
> +#define SLEEP_UNIT		1			/* 1ms */

I know I pointed you to msleep() ... sorry, I was wrong. For a
1 ms sleep the recommendation is to use usleep_range()

See this write-up in Documentation/timers/timers-howto.rst:

                - Why not msleep for (1ms - 20ms)?
                        Explained originally here:
                                https://lore.kernel.org/r/15327.1186166232@lwn.net

                        msleep(1~20) may not do what the caller intends, and
                        will often sleep longer (~20 ms actual sleep for any
                        value given in the 1~20ms range). In many cases this
                        is not the desired behavior.

To answer the question posed in that document on "What is a good range?"

I don't think injection cares too much about precision here. Maybe go
with

	usleep_range(1000, 5000);
[with #defines for SLEEP_UNIT_MIN, SLEEP_UNIT_MAX instead of those
numbers]

> +/* Firmware should respond within 1 seconds */
> +#define FIRMWARE_TIMEOUT	(1 * MSEC_PER_SEC)
>  #define ACPI5_VENDOR_BIT	BIT(31)
>  #define MEM_ERROR_MASK		(ACPI_EINJ_MEMORY_CORRECTABLE | \
>  				ACPI_EINJ_MEMORY_UNCORRECTABLE | \
> @@ -40,6 +40,8 @@
>   * ACPI version 5 provides a SET_ERROR_TYPE_WITH_ADDRESS action.
>   */
>  static int acpi5;
> +static int timeout_default = FIRMWARE_TIMEOUT;
> +module_param(timeout_default, int, 0644);

You've set the default to 1 second. Who would use this parameter?
Do you anticipate systems that take even longer to inject?
A user might set a shorter limit ... but I don't see why they
would want to.

>  
>  struct set_error_type_with_address {
>  	u32	type;
> @@ -171,12 +173,12 @@ static int einj_get_available_error_type(u32 *type)
>  
>  static int einj_timedout(u64 *t)
>  {
> -	if ((s64)*t < SPIN_UNIT) {
> +	if ((s64)*t < SLEEP_UNIT) {
>  		pr_warn(FW_WARN "Firmware does not respond in time\n");
>  		return 1;
>  	}
> -	*t -= SPIN_UNIT;
> -	ndelay(SPIN_UNIT);
> +	*t -= SLEEP_UNIT;
> +	msleep(SLEEP_UNIT);
>  	touch_nmi_watchdog();

Since we are sleeping instead of spinning, maybe we don't need to
touch the nmi watchdog?

>  	return 0;
>  }
> @@ -403,7 +405,7 @@ static int __einj_error_inject(u32 type, u32 flags, u64 param1, u64 param2,
>  			       u64 param3, u64 param4)
>  {
>  	struct apei_exec_context ctx;
> -	u64 val, trigger_paddr, timeout = FIRMWARE_TIMEOUT;
> +	u64 val, trigger_paddr, timeout = timeout_default;
>  	int rc;
>  
>  	einj_exec_ctx_init(&ctx);
> -- 
> 2.20.1.12.g72788fdb
> 

-Tony

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