Re: [Intel-gfx] [PATCH v7 06/15] mei: gsc: use polling instead of interrupts

["Ceraolo Spurio, Daniele" <daniele.ceraolospurio@intel.com>]

On 8/6/2022 5:26 AM, Tomas Winkler wrote:
> A work-around for a HW issue in XEHPSDV that manifests itself when SW reads
> a gsc register when gsc is sending an interrupt. The work-around is
> to disable interrupts and to use polling instead.
>
> Cc: James Ausmus <james.ausmus@intel.com>
> Signed-off-by: Vitaly Lubart <vitaly.lubart@intel.com>
> Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
> Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
> ---
>   drivers/misc/mei/gsc-me.c | 48 ++++++++++++++++++++++++++------
>   drivers/misc/mei/hw-me.c  | 58 ++++++++++++++++++++++++++++++++++++---
>   drivers/misc/mei/hw-me.h  | 12 ++++++++
>   3 files changed, 105 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/misc/mei/gsc-me.c b/drivers/misc/mei/gsc-me.c
> index c8145e9b62b6..2caba3a9ac35 100644
> --- a/drivers/misc/mei/gsc-me.c
> +++ b/drivers/misc/mei/gsc-me.c
> @@ -13,6 +13,7 @@
>   #include <linux/ktime.h>
>   #include <linux/delay.h>
>   #include <linux/pm_runtime.h>
> +#include <linux/kthread.h>
>   
>   #include "mei_dev.h"
>   #include "hw-me.h"
> @@ -66,13 +67,28 @@ static int mei_gsc_probe(struct auxiliary_device *aux_dev,
>   
>   	dev_set_drvdata(device, dev);
>   
> -	ret = devm_request_threaded_irq(device, hw->irq,
> -					mei_me_irq_quick_handler,
> -					mei_me_irq_thread_handler,
> -					IRQF_ONESHOT, KBUILD_MODNAME, dev);
> -	if (ret) {
> -		dev_err(device, "irq register failed %d\n", ret);
> -		goto err;
> +	/* use polling */
> +	if (mei_me_hw_use_polling(hw)) {
> +		mei_disable_interrupts(dev);
> +		mei_clear_interrupts(dev);
> +		init_waitqueue_head(&hw->wait_active);
> +		hw->is_active = true; /* start in active mode for initialization */
> +		hw->polling_thread = kthread_run(mei_me_polling_thread, dev,
> +						 "kmegscirqd/%s", dev_name(device));
> +		if (IS_ERR(hw->polling_thread)) {
> +			ret = PTR_ERR(hw->polling_thread);
> +			dev_err(device, "unable to create kernel thread: %d\n", ret);
> +			goto err;
> +		}
> +	} else {
> +		ret = devm_request_threaded_irq(device, hw->irq,
> +						mei_me_irq_quick_handler,
> +						mei_me_irq_thread_handler,
> +						IRQF_ONESHOT, KBUILD_MODNAME, dev);
> +		if (ret) {
> +			dev_err(device, "irq register failed %d\n", ret);
> +			goto err;
> +		}
>   	}
>   
>   	pm_runtime_get_noresume(device);
> @@ -98,7 +114,8 @@ static int mei_gsc_probe(struct auxiliary_device *aux_dev,
>   
>   register_err:
>   	mei_stop(dev);
> -	devm_free_irq(device, hw->irq, dev);
> +	if (!mei_me_hw_use_polling(hw))
> +		devm_free_irq(device, hw->irq, dev);
>   
>   err:
>   	dev_err(device, "probe failed: %d\n", ret);
> @@ -119,12 +136,17 @@ static void mei_gsc_remove(struct auxiliary_device *aux_dev)
>   
>   	mei_stop(dev);
>   
> +	hw = to_me_hw(dev);
> +	if (mei_me_hw_use_polling(hw))
> +		kthread_stop(hw->polling_thread);
> +
>   	mei_deregister(dev);
>   
>   	pm_runtime_disable(&aux_dev->dev);
>   
>   	mei_disable_interrupts(dev);
> -	devm_free_irq(&aux_dev->dev, hw->irq, dev);
> +	if (!mei_me_hw_use_polling(hw))
> +		devm_free_irq(&aux_dev->dev, hw->irq, dev);
>   }
>   
>   static int __maybe_unused mei_gsc_pm_suspend(struct device *device)
> @@ -185,6 +207,9 @@ static int  __maybe_unused mei_gsc_pm_runtime_suspend(struct device *device)
>   	if (mei_write_is_idle(dev)) {
>   		hw = to_me_hw(dev);
>   		hw->pg_state = MEI_PG_ON;
> +
> +		if (mei_me_hw_use_polling(hw))
> +			hw->is_active = false;
>   		ret = 0;
>   	} else {
>   		ret = -EAGAIN;
> @@ -209,6 +234,11 @@ static int __maybe_unused mei_gsc_pm_runtime_resume(struct device *device)
>   	hw = to_me_hw(dev);
>   	hw->pg_state = MEI_PG_OFF;
>   
> +	if (mei_me_hw_use_polling(hw)) {
> +		hw->is_active = true;
> +		wake_up(&hw->wait_active);
> +	}
> +
>   	mutex_unlock(&dev->device_lock);
>   
>   	irq_ret = mei_me_irq_thread_handler(1, dev);
> diff --git a/drivers/misc/mei/hw-me.c b/drivers/misc/mei/hw-me.c
> index befa491e3344..46559517a902 100644
> --- a/drivers/misc/mei/hw-me.c
> +++ b/drivers/misc/mei/hw-me.c
> @@ -10,6 +10,7 @@
>   #include <linux/interrupt.h>
>   #include <linux/pm_runtime.h>
>   #include <linux/sizes.h>
> +#include <linux/delay.h>
>   
>   #include "mei_dev.h"
>   #include "hbm.h"
> @@ -327,9 +328,12 @@ static void mei_me_intr_clear(struct mei_device *dev)
>    */
>   static void mei_me_intr_enable(struct mei_device *dev)
>   {
> -	u32 hcsr = mei_hcsr_read(dev);
> +	u32 hcsr;
> +
> +	if (mei_me_hw_use_polling(to_me_hw(dev)))
> +		return;
>   
> -	hcsr |= H_CSR_IE_MASK;
> +	hcsr = mei_hcsr_read(dev) | H_CSR_IE_MASK;
>   	mei_hcsr_set(dev, hcsr);
>   }
>   
> @@ -354,6 +358,9 @@ static void mei_me_synchronize_irq(struct mei_device *dev)
>   {
>   	struct mei_me_hw *hw = to_me_hw(dev);
>   
> +	if (mei_me_hw_use_polling(hw))
> +		return;
> +
>   	synchronize_irq(hw->irq);
>   }
>   
> @@ -380,7 +387,10 @@ static void mei_me_host_set_ready(struct mei_device *dev)
>   {
>   	u32 hcsr = mei_hcsr_read(dev);
>   
> -	hcsr |= H_CSR_IE_MASK | H_IG | H_RDY;
> +	if (!mei_me_hw_use_polling(to_me_hw(dev)))
> +		hcsr |= H_CSR_IE_MASK;
> +
> +	hcsr |=  H_IG | H_RDY;
>   	mei_hcsr_set(dev, hcsr);
>   }
>   
> @@ -1176,7 +1186,7 @@ static int mei_me_hw_reset(struct mei_device *dev, bool intr_enable)
>   
>   	hcsr |= H_RST | H_IG | H_CSR_IS_MASK;
>   
> -	if (!intr_enable)
> +	if (!intr_enable || mei_me_hw_use_polling(to_me_hw(dev)))
>   		hcsr &= ~H_CSR_IE_MASK;
>   
>   	dev->recvd_hw_ready = false;
> @@ -1331,6 +1341,46 @@ irqreturn_t mei_me_irq_thread_handler(int irq, void *dev_id)
>   }
>   EXPORT_SYMBOL_GPL(mei_me_irq_thread_handler);
>   
> +#define MEI_POLLING_TIMEOUT_ACTIVE 100
> +#define MEI_POLLING_TIMEOUT_IDLE   500
> +
> +int mei_me_polling_thread(void *_dev)
> +{
> +	struct mei_device *dev = _dev;
> +	irqreturn_t irq_ret;
> +	long polling_timeout = MEI_POLLING_TIMEOUT_ACTIVE;
> +
> +	dev_dbg(dev->dev, "kernel thread is running\n");
> +	while (!kthread_should_stop()) {
> +		struct mei_me_hw *hw = to_me_hw(dev);
> +		u32 hcsr;
> +
> +		wait_event_timeout(hw->wait_active,
> +				   hw->is_active || kthread_should_stop(),
> +				   msecs_to_jiffies(MEI_POLLING_TIMEOUT_IDLE));
> +
> +		if (kthread_should_stop())
> +			break;
> +
> +		hcsr = mei_hcsr_read(dev);
> +		if (me_intr_src(hcsr)) {
> +			polling_timeout = MEI_POLLING_TIMEOUT_ACTIVE;
> +			irq_ret = mei_me_irq_thread_handler(1, dev);
> +			if (irq_ret != IRQ_HANDLED)
> +				dev_err(dev->dev, "irq_ret %d\n", irq_ret);
> +		} else {
> +			polling_timeout = clamp_val(polling_timeout + MEI_POLLING_TIMEOUT_ACTIVE,
> +						    MEI_POLLING_TIMEOUT_ACTIVE,
> +						    MEI_POLLING_TIMEOUT_IDLE);
> +		}
> +
> +		schedule_timeout_interruptible(msecs_to_jiffies(polling_timeout));
> +	}

IMO this loop could have used a couple of comments to make it easier to 
understand what's going on with the various waits and timeouts. Not a 
blocker.

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>

Daniele

> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(mei_me_polling_thread);
> +
>   static const struct mei_hw_ops mei_me_hw_ops = {
>   
>   	.trc_status = mei_me_trc_status,
> diff --git a/drivers/misc/mei/hw-me.h b/drivers/misc/mei/hw-me.h
> index a071c645e905..ca09274ac299 100644
> --- a/drivers/misc/mei/hw-me.h
> +++ b/drivers/misc/mei/hw-me.h
> @@ -51,6 +51,8 @@ struct mei_cfg {
>    * @d0i3_supported: di03 support
>    * @hbuf_depth: depth of hardware host/write buffer in slots
>    * @read_fws: read FW status register handler
> + * @wait_active: the polling thread activity wait queue
> + * @is_active: the device is active
>    */
>   struct mei_me_hw {
>   	const struct mei_cfg *cfg;
> @@ -60,10 +62,19 @@ struct mei_me_hw {
>   	bool d0i3_supported;
>   	u8 hbuf_depth;
>   	int (*read_fws)(const struct mei_device *dev, int where, u32 *val);
> +	/* polling */
> +	struct task_struct *polling_thread;
> +	wait_queue_head_t wait_active;
> +	bool is_active;
>   };
>   
>   #define to_me_hw(dev) (struct mei_me_hw *)((dev)->hw)
>   
> +static inline bool mei_me_hw_use_polling(const struct mei_me_hw *hw)
> +{
> +	return hw->irq < 0;
> +}
> +
>   /**
>    * enum mei_cfg_idx - indices to platform specific configurations.
>    *
> @@ -127,5 +138,6 @@ int mei_me_pg_exit_sync(struct mei_device *dev);
>   
>   irqreturn_t mei_me_irq_quick_handler(int irq, void *dev_id);
>   irqreturn_t mei_me_irq_thread_handler(int irq, void *dev_id);
> +int mei_me_polling_thread(void *_dev);
>   
>   #endif /* _MEI_INTERFACE_H_ */