[RFC PATCH] ARM: DRA: hwmod: RTC: Add reset function for RTC

[Paul Walmsley]

Hi Lokesh 

On Tue, 25 Nov 2014, Lokesh Vutla wrote:

> Hi Paul,
> On Thursday 20 November 2014 10:26 PM, Paul Walmsley wrote:
> > On Thu, 20 Nov 2014, Lokesh Vutla wrote:
> > 
> >> On Monday 17 November 2014 10:13 AM, Lokesh Vutla wrote:
> >>> RTC IP have kicker feature which prevents spurious writes to its registers.
> >>> In order to write into any of the RTC registers, KICK values has te be
> >>> written to KICK registers. Currently hwmod is updating the IDLEMODE in rtc
> >>> sysconfig register without writing into any kick register which is a noop.
> >>> When autoidle is allowed for rtc, interruts are not received until IDLEMODE
> >>> is set to SIDLE_SMART_WKUP.
> >>> Adding a reset function to unlock RTC registers so that IDLEMODE is
> >>> updated.
> >> Ping..!!
> >> Is this patch acceptable?
> > 
> > Lokesh
> > 
> > 1. This looks like a fix.  Is this intended to go in as a v3.18-rc patch, 
> > or against v3.19?  If so it would be very helpful for the maintainers if 
> > you were to state that somewhere.
> Yes. This is a fix, intended to go in 3.18-rc. Sorry should have
> mentioned it.

A few questions.  Do you know when this problem started (in terms of 
kernel versions)?

Also: the patch description states that this is only a problem when 
autoidle is allowed for RTC.  What enables autoidle for RTC - the RTCSS 
driver?  Or does hwmod wind up doing this after the RTCSS driver unlocks 
it?

> > 2. Your patch unlocks the RTC registers, but never relocks it.  This seems 
> > to defeat the point of the spurious write protection.  Shouldn't your 
> > patch only unlock the RTC immediately before the hwmod code touches the 
> > RTC registers, and then relock it immediately afterwards, per SPRUHZ6 
> > section 23.4.3.3?  If so then the .reset function pointer is the wrong 
> > place for this; I would suggest adding some .lock and .unlock function 
> > pointers that are to be called before and after any register write to the 
> > IP block.
> Yeah I agree with you.
> Currently rtc driver unlocks these kick registers in probe and leaves it unlocks for
> further use.
> But if hwmod does unlock and lock for every sysconfig write driver should also
> implement unlock and lock for every rtc register write, which adds an extra overhead.
> I am not sure if some one writes into rtc registers other than hwmod and driver.
> IMO we can leave it unlocked as the driver does.

I would think that the best approach would be to set up .lock and .unlock 
function pointers, then add a temporary hwmod flag that, if set, would 
prevent the .lock function from ever being called.  Then once the driver 
is fixed, that flag can be dropped.

> > 3. Your macros don't mention DRA7xx specifically.  Does this sequence 
> > apply to some other TI chips, or just DRA7xx?  Please document this in a 
> > comment above the macros, and possibly change the name of the macros to 
> > refer to DRA7XX.
> This sequence applies to AM43xx and AM33xx also. So made it generic.
> Ill document it.

OK but it would need more than just documentation, right?  Wouldn't the 
hwmod data also need to be modified for AM33xx/AM43xx to add the .reset 
function pointer?  Any reason why folks wouldn't have seen this problem on 
AM33xx/AM43xx?


- Paul