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

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Date: Wed, 24 May 2023 16:29:01 -0500
From: Judith Mendez <jm@...com>
To: Simon Horman <simon.horman@...igine.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

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.

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


~Judith