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

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Date:   Tue, 23 May 2023 13:09:54 +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 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;
       |             ^~~

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