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Subject: Re: [PATCH] platform/x86: ISST: Account for increased timeout in some
 cases
To:     Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        mgross@linux.intel.com
Cc:     platform-driver-x86@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210330220840.3113959-1-srinivas.pandruvada@linux.intel.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <263e6c6f-68d0-fcf3-0759-d8922ff0336a@redhat.com>
Date:   Wed, 7 Apr 2021 14:38:39 +0200
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Hi,

On 3/31/21 12:08 AM, Srinivas Pandruvada wrote:
> In some cases when firmware is busy or updating, some mailbox commands
> still timeout on some newer CPUs. To fix this issue, change how we
> process timeout.
> 
> With this change, replaced timeout from using simple count with real
> timeout in micro-seconds using ktime. When the command response takes
> more than average processing time, yield to other tasks. The worst case
> timeout is extended upto 1 milli-second.
> 
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

Thank you for your patch, I've applied this patch to my review-hans 
branch:
https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/log/?h=review-hans

Note it will show up in my review-hans branch once I've pushed my
local branch there, which might take a while.

Once I've run some tests on this branch the patches there will be
added to the platform-drivers-x86/for-next branch and eventually
will be included in the pdx86 pull-request to Linus for the next
merge-window.

Regards,

Hans


> ---
>  .../intel_speed_select_if/isst_if_mbox_pci.c  | 33 +++++++++++++------
>  1 file changed, 23 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/platform/x86/intel_speed_select_if/isst_if_mbox_pci.c b/drivers/platform/x86/intel_speed_select_if/isst_if_mbox_pci.c
> index a2a2d923e60c..df1fc6c719f3 100644
> --- a/drivers/platform/x86/intel_speed_select_if/isst_if_mbox_pci.c
> +++ b/drivers/platform/x86/intel_speed_select_if/isst_if_mbox_pci.c
> @@ -21,12 +21,16 @@
>  #define PUNIT_MAILBOX_BUSY_BIT		31
>  
>  /*
> - * The average time to complete some commands is about 40us. The current
> - * count is enough to satisfy 40us. But when the firmware is very busy, this
> - * causes timeout occasionally.  So increase to deal with some worst case
> - * scenarios. Most of the command still complete in few us.
> + * The average time to complete mailbox commands is less than 40us. Most of
> + * the commands complete in few micro seconds. But the same firmware handles
> + * requests from all power management features.
> + * We can create a scenario where we flood the firmware with requests then
> + * the mailbox response can be delayed for 100s of micro seconds. So define
> + * two timeouts. One for average case and one for long.
> + * If the firmware is taking more than average, just call cond_resched().
>   */
> -#define OS_MAILBOX_RETRY_COUNT		100
> +#define OS_MAILBOX_TIMEOUT_AVG_US	40
> +#define OS_MAILBOX_TIMEOUT_MAX_US	1000
>  
>  struct isst_if_device {
>  	struct mutex mutex;
> @@ -35,11 +39,13 @@ struct isst_if_device {
>  static int isst_if_mbox_cmd(struct pci_dev *pdev,
>  			    struct isst_if_mbox_cmd *mbox_cmd)
>  {
> -	u32 retries, data;
> +	s64 tm_delta = 0;
> +	ktime_t tm;
> +	u32 data;
>  	int ret;
>  
>  	/* Poll for rb bit == 0 */
> -	retries = OS_MAILBOX_RETRY_COUNT;
> +	tm = ktime_get();
>  	do {
>  		ret = pci_read_config_dword(pdev, PUNIT_MAILBOX_INTERFACE,
>  					    &data);
> @@ -48,11 +54,14 @@ static int isst_if_mbox_cmd(struct pci_dev *pdev,
>  
>  		if (data & BIT_ULL(PUNIT_MAILBOX_BUSY_BIT)) {
>  			ret = -EBUSY;
> +			tm_delta = ktime_us_delta(ktime_get(), tm);
> +			if (tm_delta > OS_MAILBOX_TIMEOUT_AVG_US)
> +				cond_resched();
>  			continue;
>  		}
>  		ret = 0;
>  		break;
> -	} while (--retries);
> +	} while (tm_delta < OS_MAILBOX_TIMEOUT_MAX_US);
>  
>  	if (ret)
>  		return ret;
> @@ -74,7 +83,8 @@ static int isst_if_mbox_cmd(struct pci_dev *pdev,
>  		return ret;
>  
>  	/* Poll for rb bit == 0 */
> -	retries = OS_MAILBOX_RETRY_COUNT;
> +	tm_delta = 0;
> +	tm = ktime_get();
>  	do {
>  		ret = pci_read_config_dword(pdev, PUNIT_MAILBOX_INTERFACE,
>  					    &data);
> @@ -83,6 +93,9 @@ static int isst_if_mbox_cmd(struct pci_dev *pdev,
>  
>  		if (data & BIT_ULL(PUNIT_MAILBOX_BUSY_BIT)) {
>  			ret = -EBUSY;
> +			tm_delta = ktime_us_delta(ktime_get(), tm);
> +			if (tm_delta > OS_MAILBOX_TIMEOUT_AVG_US)
> +				cond_resched();
>  			continue;
>  		}
>  
> @@ -96,7 +109,7 @@ static int isst_if_mbox_cmd(struct pci_dev *pdev,
>  		mbox_cmd->resp_data = data;
>  		ret = 0;
>  		break;
> -	} while (--retries);
> +	} while (tm_delta < OS_MAILBOX_TIMEOUT_MAX_US);
>  
>  	return ret;
>  }
>