From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lee Jones <lee.jones@linaro.org>
Subject: Re: [PATCH RESEND v2 2/7] mfd: cros_ec: Add char dev and virtual dev
 pointers
Date: Tue, 20 Jan 2015 16:51:27 +0000
Message-ID: <20150120165127.GG30656@x1>
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To: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Cc: Olof Johansson <olof@lixom.net>, Doug Anderson <dianders@chromium.org>, Bill Richardson <wfrichar@chromium.org>, Simon Glass <sjg@google.com>, Gwendal Grignou <gwendal@google.com>, Jonathan Corbet <corbet@lwn.net>, linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org
List-Id: linux-samsung-soc@vger.kernel.org

On Tue, 20 Jan 2015, Javier Martinez Canillas wrote:

> Hello Lee,
>=20
> On 01/20/2015 05:36 PM, Lee Jones wrote:
> >> >=20
> >> > Is this safe?  Are you sure it's okay to provide an interface fr=
om
> >> > userspace to read (kernel?) memory?
> >> >
> >>=20
> >> This interface is not to read any kernel memory but only the memor=
y mapped
> >> I/O region for the Low Pin Count (LPC) bus. So user-space only can=
 choose
> >> and offset and a number of bytes using the CROS_EC_DEV_IOCRDMEM io=
ctl cmd
> >> which uses the following structure as argument:
> >>=20
> >> /*
> >>  * @offset: within EC_LPC_ADDR_MEMMAP region
> >>  * @bytes: number of bytes to read. zero means "read a string" (in=
cluding '\0')
> >>  *         (at most only EC_MEMMAP_SIZE bytes can be read)
> >>  * @buffer: where to store the result
> >>  * ioctl returns the number of bytes read, negative on error
> >>  */
> >> struct cros_ec_readmem {
> >>         uint32_t offset;
> >>         uint32_t bytes;
> >>         uint8_t buffer[EC_MEMMAP_SIZE];
> >> };
> >>=20
> >> The cros_ec_lpc_readmem() handler that the function pointer is set=
 only
> >> reads bytes from EC_LPC_ADDR_MEMMAP + offset if offset < EC_MEMMAP=
_SIZE
> >> and the data is copied to the user-space buffer from the structure=
 passed
> >> as argument with copy_to_user().
> >>=20
> >> So in that sense is similar to the spidev or i2c-dev interfaces th=
at are
> >> used to access these buses from user-space.
> >=20
> > Very well.  The purpose of my question was to be provocative and to
> > make you think about the interface.  As long as you're sure it can'=
t
> > be abused, then I'm happy.
> >=20
>=20
> Ok, thanks a lot. Does it mean I've your Acked-by for this patch too?

Yes: Acked-by: Lee Jones <lee.jones@linaro.org>

--=20
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org =E2=94=82 Open source software for ARM SoCs
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