linux-kernel - Re: [PATCH 3/5] i2c: omap: handle all irqs befor unblocking omap_i2c_xfer

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Date:	Wed, 19 Jun 2013 22:44:14 +0300
From:	Felipe Balbi <balbi@...com>
To:	Grygorii Strashko <grygorii.strashko@...com>
CC:	<balbi@...com>, Wolfram Sang <wsa@...-dreams.de>,
	Tony Lindgren <tony@...mide.com>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-i2c@...r.kernel.org>, Kevin Hilman <khilman@...aro.org>
Subject: Re: [PATCH 3/5] i2c: omap: handle all irqs befor unblocking
 omap_i2c_xfer_msg()

On Wed, Jun 19, 2013 at 09:43:04PM +0300, Grygorii Strashko wrote:
> Hi Felipe,
> On 06/07/2013 10:05 PM, Felipe Balbi wrote:
> >Hi,
> >
> >On Fri, Jun 07, 2013 at 09:46:06PM +0300, Grygorii Strashko wrote:
> >>ARDY|NACK and ARDY|AL are set together in OMAP_I2C_STAT_REG, which will be
> >Have you seen that happen ever ? AL is Arbitration Lost, we never put
> >OMAP in a multi-master environment before.
> This is an example from real life:
> [    0.271942] omap_i2c omap_i2c.1: bus 1 rev2.4.0 at 400 kHz
> [    1.283416] omap_i2c omap_i2c.1: timeout waiting for bus ready
> [    1.300109] OMAP_I2C DEBUG: stat=1001
> [    1.300140] omap_i2c omap_i2c.1: Arbitration lost
> [    1.300140] OMAP_I2C DEBUG: IE=601F
> [    1.300140] OMAP_I2C DEBUG: STAT=1000
> [    1.300170] OMAP_I2C DEBUG: IV=636F
> [    1.300170] OMAP_I2C DEBUG: WE=636F
> [    1.300170] OMAP_I2C DEBUG: SYSS=1
> [    1.300170] OMAP_I2C DEBUG: BUF=707
> [    1.300201] OMAP_I2C DEBUG: CNT=1
> [    1.300201] OMAP_I2C DEBUG: DATA=1
> [    1.300201] OMAP_I2C DEBUG: SYSC=215
> [    1.300201] OMAP_I2C DEBUG: CON=8200
> [    1.300231] OMAP_I2C DEBUG: OA=0
> [    1.300231] OMAP_I2C DEBUG: SA=49
> [    1.300231] OMAP_I2C DEBUG: PSC=9
> [    1.300262] OMAP_I2C DEBUG: SCLL=9
> [    1.300262] OMAP_I2C DEBUG: SCLH=3
> [    1.300262] OMAP_I2C DEBUG: SYSTEST=1E0
> [    1.300262] OMAP_I2C DEBUG: BUFSTAT=4000
> 
> and my headache now :..(

have you looked for erratas around that ? Maybe you just found a silicon
issue. Why is AL bit being set ? Have you tried to reach the IP owner ?

If there are no other I2C masters in the system, there will be no
arbitration, hence we would never loose the arbitration.

> >ARDY | NACK I also find it a bit hard for those two to happen together
> >since ARDY will be set when you can change controller's register
> >*again*, mening that a transfer has completed.
> There are examples:
> [    3.544952] omap_i2c 48060000.i2c: IRQ (ISR = 0x0006)
> 
> [   25.574523] omap_i2c 48350000.i2c: IRQ (ISR = 0x0014)
> [   25.579925] omap_i2c 48350000.i2c: IRQ (ISR = 0x0012)
> 
> to see it - enable debug output in omap_i2c_isr_thread:
>         dev_dbg(dev->dev, "IRQ (ISR = 0x%04x)\n", stat);

then you need to figure out why that's happening, right ? What do you do
to trigger that particular condition, have you looked in the wire to see
if you find a real NACK or is the OMAP I2C controller misbehaving ?

> >Also, we need to follow what the programming model says. And, I don't
> >have docs with me right now, but IIRC it tells us to bail out if any of
> >the error conditions are met.
> >
> yep, but first of all - all IRQs need to be acked before exit.

that's alright, then fix only that... OTOH, you don't want to ack a
read while data is still sitting in the FIFO, data you haven't read out
of the FIFO, I mean. Not sure if that could happen though.

-- 
balbi

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