linux-kernel - Re: [PATCH v2 1/2] mfd: viperboard: allocate I/O buffer separately

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Message-ID: <20140924101206.GD19999@lee--X1>
Date:	Wed, 24 Sep 2014 11:12:06 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Octavian Purdila <octavian.purdila@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	johan@...nel.org, Octavian Purdila <octavian.purdila@...el.com>
Subject: Re: [PATCH v2 1/2] mfd: viperboard: allocate I/O buffer separately

On Mon, 22 Sep 2014, Octavian Purdila wrote:

> Currently the I/O buffer is allocated part of the device status
> structure, potentially sharing the same cache line with other members
> in this structure.
> 
> Allocate the buffer separately, to avoid the I/O operations corrupting
> the device status structure due to cache line sharing.
> 
> Compiled tested only as I don't have access to hardware.
> 
> Signed-off-by: Octavian Purdila <octavian.purdila@...el.com>
> ---
>  drivers/mfd/viperboard.c       | 8 ++++++++
>  include/linux/mfd/viperboard.h | 2 +-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mfd/viperboard.c b/drivers/mfd/viperboard.c
> index e00f534..5f62f4e 100644
> --- a/drivers/mfd/viperboard.c
> +++ b/drivers/mfd/viperboard.c
> @@ -64,6 +64,12 @@ static int vprbrd_probe(struct usb_interface *interface,
>  		return -ENOMEM;
>  	}
>  
> +	vb->buf = kzalloc(sizeof(struct vprbrd_i2c_write_msg), GFP_KERNEL);

Can you obtain the 'struct device' first then use managed resources
(devm_*)?

> +	if (vb->buf == NULL) {
> +		ret = -ENOMEM;
> +		goto error;
> +	}
> +
>  	mutex_init(&vb->lock);
>  
>  	vb->usb_dev = usb_get_dev(interface_to_usbdev(interface));
> @@ -105,6 +111,7 @@ static int vprbrd_probe(struct usb_interface *interface,
>  error:
>  	if (vb) {
>  		usb_put_dev(vb->usb_dev);
> +		kfree(vb->buf);

Then you don't need this.

>  		kfree(vb);
>  	}
>  
> @@ -118,6 +125,7 @@ static void vprbrd_disconnect(struct usb_interface *interface)
>  	mfd_remove_devices(&interface->dev);
>  	usb_set_intfdata(interface, NULL);
>  	usb_put_dev(vb->usb_dev);
> +	kfree(vb->buf);

Or this.

>  	kfree(vb);
>  
>  	dev_dbg(&interface->dev, "disconnected\n");
> diff --git a/include/linux/mfd/viperboard.h b/include/linux/mfd/viperboard.h
> index 1934528..af928d0 100644
> --- a/include/linux/mfd/viperboard.h
> +++ b/include/linux/mfd/viperboard.h
> @@ -103,7 +103,7 @@ struct vprbrd_i2c_addr_msg {
>  struct vprbrd {
>  	struct usb_device *usb_dev; /* the usb device for this device */
>  	struct mutex lock;
> -	u8 buf[sizeof(struct vprbrd_i2c_write_msg)];
> +	u8 *buf;
>  	struct platform_device pdev;
>  };
>  

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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