Re: [PATCH] can: c_can: use regmap_update_bits() to modify RAMINIT register

[Roger Quadros <rogerq@ti.com>]

On 12/01/15 14:05, Mark Brown wrote:
> On Mon, Jan 12, 2015 at 12:02:21PM +0200, Roger Quadros wrote:
>> +Mark with correct id.
> 
> Please fix your mail client to word wrap within paragraphs, it amkes
> your mail more legible.

Fixed now. Thanks for pointing out.

> 
>>> The problem here is we can't use regmap_update_bits() because we need to write a 1 to the DONE bit to clear it and _regmap_update_bits() doesn't allow us to do that because of commit
>>> d91e8db2c3bb regmap: Suppress noop writes in regmap_update_bits()
>>>
>>> Is reverting it going to cause other issues? If yes then can we have a flag to specify forced update?
> 
> The usual thing to do here is an explicit write clearing the latch,
> either immediately after setting it or immediately before setting it.
> If the register is marked as volatile and the hardware doesn't read back
> the latched state that also does the trick.
> 

How does this work if driver has access to only 1 bit that can only be
written with 1 to clear a condition? Writing a 0 is no-op.
It can read back 0 or 1 depending on the condition.

I didn't understand the volatile trick :P.

cheers,
-roger