linux-kernel - Re: [PATCH 3/5] mfd: ti_am335x_tscadc: don't read back REG

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Message-ID: <20131219085607.GG2621@lee--X1>
Date:	Thu, 19 Dec 2013 08:56:07 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Jonathan Cameron <jic23@...nel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Zubair Lutfullah <zubair.lutfullah@...il.com>,
	Felipe Balbi <balbi@...com>, linux-iio@...r.kernel.org,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] mfd: ti_am335x_tscadc: don't read back REG_SE

On Wed, 18 Dec 2013, Sebastian Andrzej Siewior wrote:

> The purpose of reg_se_cache has been defeated. It should avoid the
> read-back of the register to avoid the latency and the fact that the
> bits are reset to 0 after the individual conversation took place.
> 
> The reason why this is required like this to work, is that read-back of
> the register removes the bits of the ADC so they do not start another
> conversation after the register is re-written from the TSC side for the
> update.
> To avoid the unrequired read-back I introduce a "set adc" variant which
> does not update the cache mask. After the conversation completes, the
> register bit is removed from the SE reister anyway and we don't plan a
> new conversation "any time soon".
> This is a small preparation for a larger sync-rework.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  drivers/iio/adc/ti_am335x_adc.c      |  2 +-
>  drivers/mfd/ti_am335x_tscadc.c       | 12 ++++++++++--
>  include/linux/mfd/ti_am335x_tscadc.h |  1 +
>  3 files changed, 12 insertions(+), 3 deletions(-)

Looks about right: Acked-by: Lee Jones <lee.jones@...aro.org>

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