mtd: pxa3xx_nand: issue with command time out

Hi Ezequiel,

On 03/04/2016 01:03 PM, Ezequiel Garcia wrote:

On 3 March 2016 at 17:16, Hamish Martin
[off-list ref] wrote:

quoted

Hi Ezequiel,

I'm glad my analysis was correct and we more fully understand the
problem now. CONFIG_PREEMPT seems to work for us now, but it does seem
like the wrong fix, and if you guys think it will not guarantee
preventing the issue then we'd rather back that change out.

Do you have any good reason for NOT enabling CONFIG_PREEMPT?

I've had very bad experiences on embedded systems when not
using CONFIG_PREEMPT, and came to the conclusion that
enable full preemption, unless there's a good reason not to.

Enabling CONFIG_PREEMPT would result in slightly lower throughput,
but maximum latency will be greatly reduced.

For instance, in a kernel without preemption, a UBI static volume check
(which happens on the first UBI static volume open call), can take
several seconds.

We don't have a good reason, it is mainly an historic artifact. We are 
happy to go with that as a fix and we are investigating it for other 
platforms too. I think it is an oversight that hasn't been given the 
thought it should.
I think we still need to consider operation of the driver without 
CONFIG_PREEMPT enabled.

quoted

I had contemplated using wait_for_completion_interruptible() but was a
bit unsure if it was safe. Do you have a proposed patch? We would be
happy to apply it to our system, turn off CONFIG_PREEMPT, and see how it
goes. Out issue is highly reproducible so I think it would be a good
first test for a change?

Sure, I can try to cook a patch for you.

Thanks for your help with this guys. Send me the patch when you have one 
you want me to test out for you.

Cheers,
Hamish M.