Re: [PATCH v4 2/3] i2c: iproc: Add Broadcom iProc I2C Driver

Uwe Kleine-König
2015-01-17T21:10:43Z

Hello,

On Sat, Jan 17, 2015 at 12:51:50PM -0800, Ray Jui wrote:
> On 1/17/2015 12:18 PM, Uwe Kleine-König wrote:
> > Hello,
> >
> > On Sat, Jan 17, 2015 at 11:58:33AM -0800, Ray Jui wrote:
> >> On 1/17/2015 8:01 AM, Uwe Kleine-König wrote:
> >>> On Fri, Jan 16, 2015 at 02:09:28PM -0800, Ray Jui wrote:
> >>>> On 1/15/2015 12:41 AM, Uwe Kleine-König wrote:
> >>>>> On Wed, Jan 14, 2015 at 02:23:32PM -0800, Ray Jui wrote:
> >>>>>> + */
> >>>>>> + val = 1 << M_CMD_START_BUSY_SHIFT;
> >>>>>> + if (msg->flags & I2C_M_RD) {
> >>>>>> + val |= (M_CMD_PROTOCOL_BLK_RD << M_CMD_PROTOCOL_SHIFT) |
> >>>>>> + (msg->len << M_CMD_RD_CNT_SHIFT);
> >>>>>> + } else {
> >>>>>> + val |= (M_CMD_PROTOCOL_BLK_WR << M_CMD_PROTOCOL_SHIFT);
> >>>>>> + }
> >>>>>> + writel(val, iproc_i2c->base + M_CMD_OFFSET);
> >>>>>> +
> >>>>>> + time_left = wait_for_completion_timeout(&iproc_i2c->done, time_left);
> >>>>>
> >>>>> When the interrupt fires here after the complete timed out and before
> >>>>> you disable the irq you still throw the result away.
> >>>> Yes, but then this comes down to the fact that if it has reached the
> >>>> point that is determined to be a timeout condition in the driver, one
> >>>> should really treat it as timeout error. In a normal condition,
> >>>> time_left should never reach zero.
> >>> I don't agree here. I'm not sure there is a real technical reason,
> >>> though. But still if you're in a "success after timeout already over"
> >>> situation it's IMHO better to interpret it as success, not timeout.
> >>>
> >> The thing is, the interrupt should never fire after
> >> wait_for_completion_timeout returns zero here. If it does, then the
> >> issue is really that the timeout value set in the driver is probably not
> >> long enough. I just checked other I2C drivers. I think the way how
> >> timeout is handled here is consistent with other I2C drivers.
> > In the presence of Clock stretching there is no (theorethical) upper
> > limit for the time needed to transfer a given message, is there? So
> > (theoretically) you can never be sure not to interrupt an ongoing
> > transfer.
> >
> Yes. No theoretical upper limit in the case when clock is stretched by
> the slave. But how would adding an additional interrupt completion check
> below help? I assume you want the the check to be like the following?
>
> time_left = wait_for_completion_timeout(&iproc_i2c->done, time_left);
>
> /* disable all interrupts */
> writel(0, iproc_i2c->base + IE_OFFSET);
>
> if (!time_left && !completion_done()) {
> dev_err(iproc_i2c->device, "transaction timed out\n");
>
> /* flush FIFOs */
> val = (1 << M_FIFO_RX_FLUSH_SHIFT) |
> (1 << M_FIFO_TX_FLUSH_SHIFT);
> writel(val, iproc_i2c->base + M_FIFO_CTRL_OFFSET);
> return -ETIMEDOUT;
> }
No, I want:

time_left = wait_for_completion_timeout(&iproc_i2c->done, time_left);

if (!transfer_was_complete) {
handle_error();
...

}

handle_successful_transfer();

and time_left == 0 is not a reliable indicator that the transfer failed.

Best regards
Uwe

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