Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753341AbbETLdP (ORCPT ); Wed, 20 May 2015 07:33:15 -0400 Received: from mail-wg0-f45.google.com ([74.125.82.45]:35732 "EHLO mail-wg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752874AbbETLdM (ORCPT ); Wed, 20 May 2015 07:33:12 -0400 Date: Wed, 20 May 2015 12:33:07 +0100 From: Lee Jones To: Javier Martinez Canillas Cc: Samuel Ortiz , Olof Johansson , Doug Anderson , Bill Richardson , Simon Glass , Gwendal Grignou , Stephen Barber , Filipe Brandenburger , Todd Broch , Alexandru M Stan , Heiko Stuebner , linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 04/10] mfd: cros_ec: Use a zero-length array for command data Message-ID: <20150520113307.GA6310@x1> References: <1431166241-15775-1-git-send-email-javier.martinez@collabora.co.uk> <1431166241-15775-5-git-send-email-javier.martinez@collabora.co.uk> <20150513111034.GH3394@x1> <55533785.7080303@collabora.co.uk> <555C3B2B.7060703@collabora.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <555C3B2B.7060703@collabora.co.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5638 Lines: 121 On Wed, 20 May 2015, Javier Martinez Canillas wrote: > Hello Lee, > > On 05/13/2015 01:37 PM, Javier Martinez Canillas wrote: > > > > On 05/13/2015 01:10 PM, Lee Jones wrote: > >> On Sat, 09 May 2015, Javier Martinez Canillas wrote: > >> > >>> 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 > >>> Signed-off-by: Javier Martinez Canillas > >>> Tested-by: Heiko Stuebner > >>> --- > >>> > >>> Changes since v1: > >>> - Add Heiko Stuebner Tested-by tag > >>> - Removed a new blank line at EOF warning. Reported by Heiko Stuebner > >>> - Use kmalloc instead of kzalloc when the message is later initialized > >>> Suggested by Gwendal Grignou > >>> - Pre-allocate struct cros_ec_command instead of dynamically allocate it > >>> whenever is possible. Suggested by Gwendal Grignou > >>> - Pre-allocate buffers for the usual cases and only allocate dynamically > >>> in the heap for bigger sizes. Suggested by Gwendal Grignou > >>> - Don't access the cros_ec_command received from user-space before doing > >>> a copy_from_user. Suggested by Gwendal Grignou > >>> - Only copy from user-space outsize bytes and copy_to_user insize bytes > >>> Suggested by Gwendal Grignou > >>> - ec_device_ioctl_xcmd() must return the numbers of bytes read and not 0 > >>> on success. Suggested by Gwendal Grignou > >>> - Rename alloc_cmd_msg to alloc_lightbar_cmd_msg. Suggested by Gwendal Grignou > >>> --- > >>> drivers/i2c/busses/i2c-cros-ec-tunnel.c | 59 ++++++++--- > >>> drivers/input/keyboard/cros_ec_keyb.c | 19 ++-- > >>> drivers/mfd/cros_ec.c | 18 ++-- > >>> drivers/mfd/cros_ec_i2c.c | 4 +- > >>> drivers/mfd/cros_ec_spi.c | 2 +- > >>> drivers/platform/chrome/cros_ec_dev.c | 66 +++++++++---- > >>> drivers/platform/chrome/cros_ec_lightbar.c | 152 +++++++++++++++++++---------- > >>> drivers/platform/chrome/cros_ec_lpc.c | 8 +- > >>> drivers/platform/chrome/cros_ec_sysfs.c | 92 +++++++++-------- > >>> include/linux/mfd/cros_ec.h | 6 +- > >>> 10 files changed, 273 insertions(+), 153 deletions(-) > >> > >> [...] > >> > >>> diff --git a/drivers/mfd/cros_ec.c b/drivers/mfd/cros_ec.c > >>> index 1574a9352a6d..ee8aa8142932 100644 > >>> --- a/drivers/mfd/cros_ec.c > >>> +++ b/drivers/mfd/cros_ec.c > >>> @@ -41,7 +41,7 @@ int cros_ec_prepare_tx(struct cros_ec_device *ec_dev, > >>> out[2] = msg->outsize; > >>> csum = out[0] + out[1] + out[2]; > >>> for (i = 0; i < msg->outsize; i++) > >>> - csum += out[EC_MSG_TX_HEADER_BYTES + i] = msg->outdata[i]; > >>> + csum += out[EC_MSG_TX_HEADER_BYTES + i] = msg->data[i]; > >>> out[EC_MSG_TX_HEADER_BYTES + msg->outsize] = (uint8_t)(csum & 0xff); > >>> > >>> return EC_MSG_TX_PROTO_BYTES + msg->outsize; > >>> @@ -75,11 +75,13 @@ int cros_ec_cmd_xfer(struct cros_ec_device *ec_dev, > >>> ret = ec_dev->cmd_xfer(ec_dev, msg); > >>> if (msg->result == EC_RES_IN_PROGRESS) { > >>> int i; > >>> - struct cros_ec_command status_msg = { }; > >>> + struct cros_ec_command *status_msg; > >>> struct ec_response_get_comms_status *status; > >>> + u8 buf[sizeof(*status_msg) + sizeof(*status)] = { }; > >> > >> This sort of thing is usually frowned upon. Can you allocate and free > >> buf's memory using the normal kernel helpers please? > >> > > > > The first version of this patch used kmalloc (actually kzalloc) and kfree > > to allocate and free the buffers but Gwendal suggested that we could > > allocate in the stack instead as an optimization [0]. > > > > I have no strong opinion on this so I'm happy to change it again when > > re-spinning the patches. > > > > [snip] > > > > > [0]: https://lkml.org/lkml/2015/4/24/8 > > > > You didn't answer if you agree with Gwendal that we can allocate things on > the stack or if you still prefer to use kmalloc/kfree. As I said I don't > have a strong argument on either approach but just want to agree to avoid > doing the same change on each revision. I don't want you to use variable names to allocate arrays like this. -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/