linux-kernel - Re: [PATCH] i2c: rk3x: fix bug that cause transfer fails in master receive mode

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Message-ID: <20140821181738.GA1443@katana>
Date:	Thu, 21 Aug 2014 13:17:38 -0500
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	Addy Ke <addy.ke@...k-chips.com>, max.schwarz@...ine.de,
	heiko@...ech.de, olof@...om.net, dianders@...omium.org,
	huangtao@...k-chips.com, hl@...k-chips.com, yzq@...k-chips.com,
	zyw@...k-chips.com, linux-kernel@...r.kernel.org,
	kever.yang@...k-chips.com, linux-rockchip@...ts.infradead.org,
	xjq@...k-chips.com, linux-i2c@...r.kernel.org,
	caesar.wang@...k-chips.com, cf@...k-chips.com, hj@...k-chips.com,
	zhengsq@...k-chips.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] i2c: rk3x: fix bug that cause transfer fails in master
 receive mode

On Thu, Aug 21, 2014 at 10:04:31PM +0400, Sergei Shtylyov wrote:
> Hello.
> 
> On 08/21/2014 09:50 PM, Addy Ke wrote:
> 
> >In rk3x SOC, the I2C controller can receive/transmit up to 32 bytes data
> >in one transaction, so the size of data to be write/read to/from
> >TXDATAx/RXDATAx must be less than or equal 32 bytes at a time.
> 
> >Test on pinky board, elan receive 158 bytes data.
> 
> >Signed-off-by: Addy Ke <addy.ke@...k-chips.com>
> >---
> >  drivers/i2c/busses/i2c-rk3x.c | 3 +++
> >  1 file changed, 3 insertions(+)
> 
> >diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
> >index 69e1185..dc0aa64 100644
> >--- a/drivers/i2c/busses/i2c-rk3x.c
> >+++ b/drivers/i2c/busses/i2c-rk3x.c
> >@@ -323,6 +323,9 @@ static void rk3x_i2c_handle_read(struct rk3x_i2c *i2c, unsigned int ipd)
> >  	/* ack interrupt */
> >  	i2c_writel(i2c, REG_INT_MBRF, REG_IPD);
> >
> >+	/* Can only handle a maximum of 32 bytes at a time */
> >+	len = (len > 32) ? 32 : len;
> 
>    Why not min(len, 32)? Or even:
> 
> 	if (len > 32)
> 		len = 32;

No silent trimming, please. The message should be rejected when the transfer is
set up. We could assign -EOVERFLOW to that type of failures, so users
will know. Sadly, I have seen other controllers having such limits :(


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