Re: [PATCH] spi: tegra: add spi driver for SLINK controller

[Stephen Warren <swarren@wwwdotorg.org>]

On 10/29/2012 10:18 AM, Laxman Dewangan wrote:
> On Monday 29 October 2012 08:47 PM, Stephen Warren wrote:
>> On 10/26/2012 12:49 PM, Laxman Dewangan wrote:
>>>>
>>>> Why not just always set SLINK_FIFO_ERROR; does it have to be set in the
>>>> write only if the status was previously asserted? If that is true, how
>>>> do you avoid a race condition where the bit gets set in SLINK_STATUS
>>>> after you read it but before you write to clear it?
>>> Status gets updated together. There is no steps of updating status.
>> Sorry, I don't understand this answer.
> 
> The status should be updated once by HW and so there is no race condition.
> HW behavior is that if the tx or Rx error occurs, it updates the status,
> generates interrupt and still continue transfer and later on, it
> generates the ready.
> In first isr, we read status, error status found and so in isr thread,
> we reset controller to stop the transfer.
> 
> So in good state, only ready bit will be set and hence writing 1 to
> clear it.
> In error state, clearing error first in ISR and in isr thread resetting
> the controller to stop the controller engine.

OK, I see why there's no race. It still seems simply to me if
tegra_slink_clear_status() just always writes all the status bits, but I
suppose it isn't a correctness issue.

>>> Is there a way to support the reset of controller. We will need this
>>> functionality.
>>
>> Why do we need to reset the controller at all; can't we simply program
>> all the (few) configuration registers? Are there HW bugs that hang the
>> controller and require a reset or something?
> 
> HW generates error,  then interrupt and still continue transfer and
> later point of time it generates the transfer done.
> We want to stop the transfer once error get detected. For this we need
> to reset controller.
> I did disabling rx and tx but still controller shows as busy.

Oh dear. Well, I guess it'll have to be OK then; we'll just have to find
a way of decoupling this API from the mach-tegra directory later:-(