Hello Nishant,
Comments inlined,
Regards
Moiz Sonasath
-----Original Message-----
From: Menon, Nishanth
Sent: Wednesday, July 15, 2009 4:43 PM
To: Sonasath, Moiz
Cc: linux-omap@xxxxxxxxxxxxxxx; Kamat, Nishant; Paul Walmsley
Subject: Re: [PATCH 3/3] [OMAP:I2C]OMAP3430 Silicon Errata 1.153
Sonasath, Moiz had written, on 07/15/2009 10:40 AM, the following:
>> When an XRDY/XDR is hit, wait for XUDF before writing data to DATA_REG.
>> Otherwise some data bytes can be lost while transferring them from the
>> memory to the I2C interface.
>>
>> Do a Busy-wait for XUDF, before writing data to DATA_REG. While waiting
>> if there is NACK | AL, set the appropriate error flags, ack the pending
>> + }
>> + cpu_relax();
>> + stat = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG);
>> + }
> this is an infinite while loop + it tries to handle error cases -
> essentially do another isr routine inside itself.
> [Moiz]
> Yes, it is a busy wait loop. But AFAIK while we come to this part of
> the code the only thing that can go wrong in the transfer is either
> the device would go off suddenly (creating a NACK) or there is an
> arbitration lost(AL). This loop takes care of these two error conditions.
> Apart from these, if the hardware is functional, the XUDF bit should
> be set as soon as the FIFO gets empty.
>
> Correct me if I am missing something.
That is exactly what I was complaining about -> why not use the existing
logic above in the code to take care of it as I indicated below? do you
see a problem with the logic I send? it is lesser code and should IMHO
take care of the same issue without the additional 3rd nested while loop
>
> How about:
> Apply [1] and the following?
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index ad8d201..e3f21af 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -728,6 +728,12 @@ omap_i2c_isr(int this_irq, void *dev_id)
> }
> if (stat & (OMAP_I2C_STAT_XRDY | OMAP_I2C_STAT_XDR)) {
> u8 num_bytes = 1;
> + if (cpu_is_omap34xx() &&
> + !(stat & OMAP_I2C_STAT_XUDF)){
> + cpu_relax();
> + continue;
> + }
> +
[Moiz]
In this alternate implementation if a NACK|AL is produced while waiting on the XUDF, it returns from the ISR (as per my patch [2/3]) without ACKING the XRDY/XDR interrupts which would make it return to the ISR again and again which looks like a problem. To accommodate this implementation, we will have to ACK XRDY/XDR before returning from the ISR.
> if (dev->fifo_size) {
> if (stat & OMAP_I2C_STAT_XRDY)
> num_bytes = dev->fifo_size;
>
>
> Regards,
> Nishanth Menon
> Ref:
> [1] http://patchwork.kernel.org/patch/32332/
--
Regards,
Nishanth Menon
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