linux-kernel - Re: [PATCH] i2c: rk3x: fix 0 length write transfers

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Date:	Thu, 02 Oct 2014 15:30:47 +0200
From:	Max Schwarz <max.schwarz@...ine.de>
To:	Alexandru M Stan <amstan@...omium.org>
Cc:	Wolfram Sang <wsa@...-dreams.de>,
	Doug Anderson <dianders@...omium.org>,
	Sonny Rao <sonnyrao@...omium.org>,
	addy ke <addy.ke@...k-chips.com>,
	Jeffy Chen <jeffy.chen@...k-chips.com>,
	ZhengShunQian <zhengsq@...k-chips.com>,
	linux-rockchip@...ts.infradead.org, heiko@...ech.de,
	linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: rk3x: fix 0 length write transfers

Hi Alexandru,

On Wednesday 01 October 2014 at 10:40:41, Alexandru M Stan wrote:
> i2cdetect -q was broken (everything was a false positive, and no transfers
> were actually being sent over i2c). The way it works is by sending a 0
> length write request and checking for NACK. This patch fixes the 0 length
> writes and actually sends them.
> 
> Reported-by: Doug Anderson <dianders@...omium.org>
> Signed-off-by: Alexandru M Stan <amstan@...omium.org>
> ---
>  drivers/i2c/busses/i2c-rk3x.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
> index b41d979..f486d0e 100644
> --- a/drivers/i2c/busses/i2c-rk3x.c
> +++ b/drivers/i2c/busses/i2c-rk3x.c
> @@ -238,7 +238,7 @@ static void rk3x_i2c_fill_transmit_buf(struct rk3x_i2c
> *i2c) for (i = 0; i < 8; ++i) {
>  		val = 0;
>  		for (j = 0; j < 4; ++j) {
> -			if (i2c->processed == i2c->msg->len)
> +			if ((i2c->processed == i2c->msg->len) && (cnt != 0))
>  				break;
> 
>  			if (i2c->processed == 0 && cnt == 0)

Yes, looks correct and makes i2cdetect work for me on Radxa Rock.

Reviewed-By: Max Schwarz <max.schwarz@...ine.de>
Tested-By: Max Schwarz <max.schwarz@...ine.de>

Cheers,
  Max
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