From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from zmta01.irigo.dk (zmta01.cabocomm.dk [193.200.44.52]) by ozlabs.org (Postfix) with ESMTP id E3724DE00B for ; Thu, 14 May 2009 18:48:31 +1000 (EST) Message-ID: <4A0BDAD6.5020005@doredevelopment.dk> Date: Thu, 14 May 2009 10:48:22 +0200 From: Esben Haabendal MIME-Version: 1.0 To: Wolfram Sang Subject: Re: [PATCH] i2c-mpc: generate START condition after STOP caused by read i2c_msg References: <4A0BD1DB.4090305@doredevelopment.dk> <20090514083453.GB3043@pengutronix.de> In-Reply-To: <20090514083453.GB3043@pengutronix.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linuxppc-dev@ozlabs.org, linux-i2c@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Wolfram Sang wrote: > On Thu, May 14, 2009 at 10:10:03AM +0200, Esben Haabendal wrote: > >> This fixes MAL (arbitration lost) bug caused by illegal use of >> RSTA (repeated START) after STOP condition generated after last byte >> of reads. >> >> > > Could you elaborate a bit, please? Like an example when the original bug > occured (so I could reproduce easily) and how this patch actually solves > the problem. > Sure. I used the following code to initialize a CS4265 chip: (simplified here for the example) static int i2c_init_chip(void) { int err=0; char write_dac_control_1[] = { 0x03, chip->regs.dac_control_1 }; char seek_chip_id[] = { 0x01 }; char write_power_control[] = { 0x02, chip->regs.power_control }; struct i2c_msg cs4265_init_cmds[] = { { chip->i2c_addr, 0, 2, write_dac_control_1 }, { chip->i2c_addr, 0, 1, seek_chip_id }, { chip->i2c_addr, I2C_M_RD, 1, ®s.chip_id }, { chip->i2c_addr, 0, 2, write_power_control }, }; err = i2c_transfer(i2c, cs4265_init_cmds, sizeof(cs4265_init_cmds)/sizeof(*cs4265_init_cmds)); if (err < 0) { printk(KERN_ERR "i2c_transfer failed: %d\n", err); return err; } return 0; } I have added some additional debug output and traces something like this: [ 36.114297] writeccr 80 [MEN] [ 36.114324] mpc_xfer: 2 bytes to 4f:W - 1 of 5 messages [ 36.120176] next 1 bytes to 4f:W [ 36.124159] mpc_write addr=4f len=2 [ 36.128044] writeccr 80 [MEN] [ 36.128062] writeccr f0 [MEN MIEN MSTA MTX] -> START [ 36.128219] I2C: SR=a2 [ 36.131528] I2C: SR=a6 [ 36.134406] I2C: SR=a2 [ 36.137165] mpc_xfer: 1 bytes to 4f:W - 2 of 5 messages [ 36.142802] next 1 bytes to 4f:R [ 36.146699] mpc_write addr=4f len=1 [ 36.150583] writeccr f4 [MEN MIEN MSTA MTX RSTA] -> repeated START [ 36.150758] I2C: SR=a2 [ 36.153851] I2C: SR=a6 [ 36.156236] mpc_xfer: 1 bytes to 4f:R - 3 of 5 messages [ 36.162081] next 2 bytes to 4f:W [ 36.166062] mpc_read addr=4f len=1 [ 36.169858] writeccr f4 [MEN MIEN MSTA MTX RSTA] -> repeated START [ 36.170031] I2C: SR=a6 [ 36.172993] writeccr e8 [MEN MIEN MSTA TXAK] -> receive & no ACK [ 36.173143] I2C: SR=a7 [ 36.175511] writeccr c8 [MEN MIEN TXAK] -> STOP [ 36.175529] mpc_xfer: 2 bytes to 4f:W - 4 of 5 messages [ 36.181804] next 2 bytes to 4f:W [ 36.185788] mpc_write addr=4f len=2 [ 36.189672] writeccr f4 [MEN MIEN MSTA MTX RSTA] -> repeated START [ 36.189704] I2C: SR=b7 [ 36.192072] I2C: MAL [ 36.195075] i2c_wait(address) error: -5 [ 36.199311] writeccr 80 The problem is that after the STOP condition, the following i2c_msg will be attempted with a repeated START, which according to specification will cause a MAL, which also happens. My MPC8360ERM reads: "Attempting a repeated START at the wrong time (or if the bus is owned by another master), results in loss of arbitration." Which I know read as it that we must own the I2C bus when using RSTA. > > >> Signed-off-by: Esben Haabendal >> --- >> drivers/i2c/busses/i2c-mpc.c | 9 +++++++-- >> 1 files changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c >> index 4af5c09..9fe05d9 100644 >> --- a/drivers/i2c/busses/i2c-mpc.c >> +++ b/drivers/i2c/busses/i2c-mpc.c >> @@ -456,17 +456,22 @@ static int mpc_xfer(struct i2c_adapter *adap, >> struct i2c_msg *msgs, int num) >> } >> >> for (i = 0; ret >= 0 && i < num; i++) { >> + int restart = i; >> pmsg = &msgs[i]; >> dev_dbg(i2c->dev, >> "Doing %s %d bytes to 0x%02x - %d of %d messages\n", >> pmsg->flags & I2C_M_RD ? "read" : "write", >> pmsg->len, pmsg->addr, i + 1, num); >> + if (i > 0 && ((pmsg-1)->flags & I2C_M_RD)) >> > > CodingStyle: Spaces around '-' > Ok. > >> + restart = 0; >> if (pmsg->flags & I2C_M_RD) >> ret = >> - mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len, i); >> + mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len, >> + restart); >> else >> ret = >> - mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len, i); >> + mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len, >> + restart); >> } >> mpc_i2c_stop(i2c); >> return (ret < 0) ? ret : num; >> -- >> 1.6.0.4 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-i2c" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > >