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

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Date: Thu, 25 May 2023 09:23:04 +0200
From: Simon Horman <simon.horman@...igine.com>
To: Judith Mendez <jm@...com>
Cc: Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
	linux-can@...r.kernel.org, Wolfgang Grandegger <wg@...ndegger.com>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Schuyler Patton <spatton@...com>, Tero Kristo <kristo@...nel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH v7 2/2] can: m_can: Add hrtimer to generate software
 interrupt

On Wed, May 24, 2023 at 04:29:01PM -0500, Judith Mendez wrote:
> 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@...com>
> > 
> > ...
> > 
> > > 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.

If it is valid for mcan_class->net->irq to be 0 in this case,
then, yes, I agree.

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