Re: Sluggish AT91 I2C driver causes SMBus timeouts

[Peter Rosin]

On 2017-10-13 15:29, Alan Cox wrote:
> On Thu, 12 Oct 2017 13:35:17 +0200
> Peter Rosin <peda@xxxxxxxxxx> wrote:
> 
>> Hi!
>>
>> I have encountered an "interesting" bug. It silently corrupts data
>> and is generally nasty...
>>
>> On an I2C bus, driven by the at91 driver and DMA (an Atmel
>> sama5d31 chip), I have an 256 byte eeprom (NXP SE97BTP). I'm using
>> Linux v4.13.
> 
> If your force the transfer to PIO does it behave ? Does the controller in
> fact need to siwtch to PIO for SMBUS ?

Like, what if I disable DMA?

I saw no way to do that, short of short-cutting a few things in the
driver code. So, did that and I cannot tickle the bug. But I don't
know if that makes me safe?

Ludovic, any reason to believe disabling DMA will prevent these
stalls, or will they just appear under different circumstances?

I used this dirty "patch" to i2c-at91.c:at91_twi_configure_dma() for
testing:

-	dev->use_dma = true;
+	//dev->use_dma = true;

Cheers,
Peter