Re: [PATCH v7 2/2] can: m_can: Add hrtimer to generate software interrupt

[Judith Mendez]

Hello Simon,

On 5/23/23 6:09 AM, Simon Horman wrote:
> On Mon, May 22, 2023 at 09:37:49PM -0500, Judith Mendez wrote:
> > Add an hrtimer to MCAN class device. Each MCAN will have its own
> > hrtimer instantiated if there is no hardware interrupt found in
> > device tree M_CAN node.
> >
> > The hrtimer will generate a software interrupt every 1 ms. In
> > 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>
>
> ...
>
> > diff --git a/drivers/net/can/m_can/m_can_platform.c b/drivers/net/can/m_can/m_can_platform.c
> > index 94dc82644113..b639c9e645d3 100644
> > --- a/drivers/net/can/m_can/m_can_platform.c
> > +++ b/drivers/net/can/m_can/m_can_platform.c
> > @@ -5,6 +5,7 @@
> >   //
> >   // Copyright (C) 2018-19 Texas Instruments Incorporated - http://www.ti.com/
> >   
> > +#include <linux/hrtimer.h>
> >   #include <linux/phy/phy.h>
> >   #include <linux/platform_device.h>
> >   
> > @@ -96,12 +97,30 @@ static int m_can_plat_probe(struct platform_device *pdev)
> >   		goto probe_fail;
> >   
> >   	addr = devm_platform_ioremap_resource_byname(pdev, "m_can");
> > -	irq = platform_get_irq_byname(pdev, "int0");
> > -	if (IS_ERR(addr) || irq < 0) {
> > -		ret = -EINVAL;
> > +	if (IS_ERR(addr)) {
> > +		ret = PTR_ERR(addr);
> >   		goto probe_fail;
> >   	}
> >   
> > +	if (device_property_present(mcan_class->dev, "interrupts") ||
> > +	    device_property_present(mcan_class->dev, "interrupt-names")) {
> > +		irq = platform_get_irq_byname(pdev, "int0");
> > +		mcan_class->polling = false;
> > +		if (irq == -EPROBE_DEFER) {
> > +			ret = -EPROBE_DEFER;
> > +			goto probe_fail;
> > +		}
> > +		if (irq < 0) {
> > +			ret = -ENXIO;
> > +			goto probe_fail;
> > +		}
> > +	} else {
> > +		mcan_class->polling = true;
> > +		dev_dbg(mcan_class->dev, "Polling enabled, initialize hrtimer");
> > +		hrtimer_init(&mcan_class->hrtimer, CLOCK_MONOTONIC,
> > +			     HRTIMER_MODE_REL_PINNED);
> > +	}
>
> Hi Judith,
>
> it seems that with this change irq is only set in the first arm of
> the above conditional. But later on it is used unconditionally.
> That is, it may be used uninitialised.
>
> Reported by gcc-12 as:
>
>   drivers/net/can/m_can/m_can_platform.c: In function 'm_can_plat_probe':
>   drivers/net/can/m_can/m_can_platform.c:150:30: warning: 'irq' may be used uninitialized [-Wmaybe-uninitialized]
>     150 |         mcan_class->net->irq = irq;
>         |         ~~~~~~~~~~~~~~~~~~~~~^~~~~
>   drivers/net/can/m_can/m_can_platform.c:86:13: note: 'irq' was declared here
>      86 |         int irq, ret = 0;
>         |             ^~~

Maybe a good solution is to initialize irq=0 here.

> > +
> >   	/* message ram could be shared */
> >   	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "message_ram");
> >   	if (!res) {
> > --
> > 2.17.1


~Judith