linux-kernel - Re: [PATCH v2] mfd: cros ec: Lock the SPI bus while holding chipselect

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Date:	Tue, 24 Nov 2015 17:00:20 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Nicolas Boichat <drinkcat@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	Javier Martinez Canillas <javier@....samsung.com>,
	Olof Johansson <olof@...om.net>, dianders@...omium.org,
	rspangler@...omium.org, gwendal@...omium.org,
	linux-spi@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v2] mfd: cros ec: Lock the SPI bus while holding
 chipselect

On Mon, 09 Nov 2015, Nicolas Boichat wrote:

> cros_ec_cmd_xfer_spi and cros_ec_pkt_xfer_spi generally work like
> this:
>  - Pull CS down (active), wait a bit, then send a command
>  - Wait for response (multiple requests)
>  - Wait a while, pull CS up (inactive)
> 
> These operations, individually, lock the SPI bus, but there is
> nothing preventing the SPI framework from interleaving messages
> intended for other devices as the bus is unlocked in between.
> 
> This is a problem as the EC expects CS to be held low for the
> whole duration.
> 
> Solution: Lock the SPI bus during the whole transaction, to make
> sure that no other messages can be interleaved.
> 
> Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> ---
> 
> v2: Move bus_unlock earlier in the functions.
> 
> Applies on top on linux-next/master (20151109)
> 
>  drivers/mfd/cros_ec_spi.c | 41 +++++++++++++++++++++++++++++------------
>  1 file changed, 29 insertions(+), 12 deletions(-)

Code changes look okay, but I think you can drop the comments.

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