Re: [RFC PATCH 5/5] can: m_can: Add hrtimer to generate software interrupt

[Oliver Hartkopp <socketcan@xxxxxxxxxxxx>]

On 4/14/23 20:20, Marc Kleine-Budde wrote:
> On 13.04.2023 17:30:51, Judith Mendez wrote:
> > Add a hrtimer to MCAN struct. Each MCAN will have its own
> > hrtimer instantiated if there is no hardware interrupt found.
> >
> > The hrtimer will generate a software interrupt every 1 ms. In
>
> Are you sure about the 1ms?

The "shortest" 11 bit CAN ID CAN frame is a Classical CAN frame with DLC 
= 0 and 1 Mbit/s (arbitration) bitrate. This should be 48 bits @1Mbit => 
~50 usecs

So it should be something about

    50 usecs * (FIFO queue len - 2)

if there is some FIFO involved, right?

Best regards,
Oliver

> > hrtimer callback, we check if there is a transaction pending by
> > reading a register, then process by calling the isr if there is.
> >
> > Signed-off-by: Judith Mendez <jm@xxxxxx>
> > ---
> >   drivers/net/can/m_can/m_can.c          | 24 ++++++++++++++++++++++--
> >   drivers/net/can/m_can/m_can.h          |  3 +++
> >   drivers/net/can/m_can/m_can_platform.c |  9 +++++++--
> >   3 files changed, 32 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> > index 8e83d6963d85..bb9d53f4d3cc 100644
> > --- a/drivers/net/can/m_can/m_can.c
> > +++ b/drivers/net/can/m_can/m_can.c
> > @@ -23,6 +23,7 @@
> >   #include <linux/pinctrl/consumer.h>
> >   #include <linux/platform_device.h>
> >   #include <linux/pm_runtime.h>
> > +#include <linux/hrtimer.h>
> >   
> >   #include "m_can.h"
> >   
> > @@ -1584,6 +1585,11 @@ static int m_can_close(struct net_device *dev)
> >   	if (!cdev->is_peripheral)
> >   		napi_disable(&cdev->napi);
> >   
> > +	if (dev->irq < 0) {
> > +		dev_info(cdev->dev, "Disabling the hrtimer\n");
>
> Make it a dev_dbg() or remove completely.
>
> > +		hrtimer_cancel(&cdev->hrtimer);
> > +	}
> > +
> >   	m_can_stop(dev);
> >   	m_can_clk_stop(cdev);
> >   	free_irq(dev->irq, dev);
> > @@ -1792,6 +1798,19 @@ static netdev_tx_t m_can_start_xmit(struct sk_buff *skb,
> >   	return NETDEV_TX_OK;
> >   }
> >   
> > +enum hrtimer_restart hrtimer_callback(struct hrtimer *timer)
> > +{
> > +	irqreturn_t ret;
>
> never read value?
>
> > +	struct m_can_classdev *cdev =
> > +		container_of(timer, struct m_can_classdev, hrtimer);
> > +
> > +	ret = m_can_isr(0, cdev->net);
> > +
> > +	hrtimer_forward_now(timer, ns_to_ktime(5 * NSEC_PER_MSEC));
>
> There's ms_to_ktime()....and the "5" doesn't match your patch
> description.
>
> > +
> > +	return HRTIMER_RESTART;
> > +}
> > +
> >   static int m_can_open(struct net_device *dev)
> >   {
> >   	struct m_can_classdev *cdev = netdev_priv(dev);
> > @@ -1836,8 +1855,9 @@ static int m_can_open(struct net_device *dev)
> >   	}
> >   
> >   	if (err < 0) {
> > -		netdev_err(dev, "failed to request interrupt\n");
> > -		goto exit_irq_fail;
> > +		dev_info(cdev->dev, "Enabling the hrtimer\n");
> > +		cdev->hrtimer.function = &hrtimer_callback;
> > +		hrtimer_start(&cdev->hrtimer, ns_to_ktime(0), HRTIMER_MODE_REL_PINNED);
>
> IMHO it makes no sense to request an IRQ if the device doesn't have one,
> and then try to fix up things in the error path. What about this?
>
> --- a/drivers/net/can/m_can/m_can.c
> +++ b/drivers/net/can/m_can/m_can.c
> @@ -1831,9 +1831,11 @@ static int m_can_open(struct net_device *dev)
>                   err = request_threaded_irq(dev->irq, NULL, m_can_isr,
>                                              IRQF_ONESHOT,
>                                              dev->name, dev);
> -        } else {
> +        } else if (dev->irq) {
>                   err = request_irq(dev->irq, m_can_isr, IRQF_SHARED, dev->name,
>                                     dev);
> +        } else {
> +                // polling
>           }
>   
>           if (err < 0) {
>
> >   	}
> >   
> >   	/* start the m_can controller */
> > diff --git a/drivers/net/can/m_can/m_can.h b/drivers/net/can/m_can/m_can.h
> > index a839dc71dc9b..ed046d77fdb9 100644
> > --- a/drivers/net/can/m_can/m_can.h
> > +++ b/drivers/net/can/m_can/m_can.h
> > @@ -28,6 +28,7 @@
> >   #include <linux/pm_runtime.h>
> >   #include <linux/slab.h>
> >   #include <linux/uaccess.h>
> > +#include <linux/hrtimer.h>
> >   
> >   /* m_can lec values */
> >   enum m_can_lec_type {
> > @@ -93,6 +94,8 @@ struct m_can_classdev {
> >   	int is_peripheral;
> >   
> >   	struct mram_cfg mcfg[MRAM_CFG_NUM];
> > +
> > +	struct hrtimer hrtimer;
> >   };
> >   
> >   struct m_can_classdev *m_can_class_allocate_dev(struct device *dev, int sizeof_priv);
> > diff --git a/drivers/net/can/m_can/m_can_platform.c b/drivers/net/can/m_can/m_can_platform.c
> > index 9c1dcf838006..53e1648e9dab 100644
> > --- a/drivers/net/can/m_can/m_can_platform.c
> > +++ b/drivers/net/can/m_can/m_can_platform.c
> > @@ -7,6 +7,7 @@
> >   
> >   #include <linux/phy/phy.h>
> >   #include <linux/platform_device.h>
> > +#include <linux/hrtimer.h>
> >   
> >   #include "m_can.h"
> >   
> > @@ -98,8 +99,12 @@ static int m_can_plat_probe(struct platform_device *pdev)
> >   	addr = devm_platform_ioremap_resource_byname(pdev, "m_can");
> >   	irq = platform_get_irq_byname(pdev, "int0");
> >   	if (IS_ERR(addr) || irq < 0) {
>
> What about the IS_ERR(addr) case?
>
> > -		ret = -EINVAL;
> > -		goto probe_fail;
> > +		if (irq == -EPROBE_DEFER) {
> > +			ret = -EPROBE_DEFER;
> > +			goto probe_fail;
> > +		}
> > +		dev_info(mcan_class->dev, "Failed to get irq, initialize hrtimer\n");
> > +		hrtimer_init(&mcan_class->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
>
> I don't like it when polling is unconditionally set up in case of an irq
> error. I'm not sure if we need an explicit device tree property....
>
> >   	}
> >   
> >   	/* message ram could be shared */
> > --
> > 2.17.1
>
> Marc