linux-kernel - Re: [RESEND PATCH 4/8] mfd: cros_ec: Use a zero-length array for command data

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Message-ID: <3714344.xf4aIv3C10@diego>
Date:	Thu, 16 Apr 2015 11:45:42 +0200
From:	Heiko Stübner <heiko@...ech.de>
To:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Cc:	Olof Johansson <olof@...om.net>, Lee Jones <lee.jones@...aro.org>,
	Doug Anderson <dianders@...omium.org>,
	Bill Richardson <wfrichar@...omium.org>,
	Simon Glass <sjg@...gle.com>,
	Gwendal Grignou <gwendal@...gle.com>,
	Stephen Barber <smbarber@...omium.org>,
	Filipe Brandenburger <filbranden@...gle.com>,
	Todd Broch <tbroch@...omium.org>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH 4/8] mfd: cros_ec: Use a zero-length array for command data

Am Montag, 6. April 2015, 18:15:02 schrieb Javier Martinez Canillas:
> Commit 1b84f2a4cd4a ("mfd: cros_ec: Use fixed size arrays to transfer
> data with the EC") modified the struct cros_ec_command fields to not
> use pointers for the input and output buffers and use fixed length
> arrays instead.
> 
> This change was made because the cros_ec ioctl API uses that struct
> cros_ec_command to allow user-space to send commands to the EC and
> to get data from the EC. So using pointers made the API not 64-bit
> safe. Unfortunately this approach was not flexible enough for all
> the use-cases since there may be a need to send larger commands
> on newer versions of the EC command protocol.
> 
> So to avoid to choose a constant length that it may be too big for
> most commands and thus wasting memory and CPU cycles on copy from
> and to user-space or having a size that is too small for some big
> commands, use a zero-length array that is both 64-bit safe and
> flexible. The same buffer is used for both output and input data
> so the maximum of these values should be used to allocate it.
> 
> Suggested-by: Gwendal Grignou <gwendal@...omium.org>
> Signed-off-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>
> ---

[...]

>  /* Module initialization */
> @@ -269,3 +301,4 @@ void ec_dev_sysfs_remove(struct cros_ec_device *ec)
>  {
>  	sysfs_remove_group(&ec->vdev->kobj, &ec_attr_group);
>  }
> +

.git/rebase-apply/patch:893: new blank line at EOF.


> diff --git a/include/linux/mfd/cros_ec.h b/include/linux/mfd/cros_ec.h
> index 14cf522123dd..7eee38abd02a 100644
> --- a/include/linux/mfd/cros_ec.h
> +++ b/include/linux/mfd/cros_ec.h

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