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

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Date:	Wed, 1 Oct 2014 15:47:06 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Alexandru M Stan <amstan@...omium.org>
Cc:	Max Schwarz <max.schwarz@...ine.de>,
	Wolfram Sang <wsa@...-dreams.de>,
	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 Stübner <heiko@...ech.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: rk3x: fix 0 length write transfers

Alex,

On Wed, Oct 1, 2014 at 10:40 AM, Alexandru M Stan <amstan@...omium.org> 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))

This looks good to me.  Basically we still need to write the address
of the device onto the bus even if there's no data.

Reviewed-by: Doug Anderson <dianders@...omium.org>
Tested-by: Doug Anderson <dianders@...omium.org>

-Doug
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