Re: OMAP4 errata i740

[Santosh Shilimkar <santosh.shilimkar@ti.com>]

On Friday 30 March 2012 02:04 PM, Archit Taneja wrote:
> On Friday 30 March 2012 02:01 PM, Santosh Shilimkar wrote:
>> + Kevin
>>
>> On Friday 30 March 2012 01:56 PM, Tomi Valkeinen wrote:
>>> On Fri, 2012-03-30 at 13:51 +0530, Shilimkar, Santosh wrote:
>>>> On Fri, Mar 30, 2012 at 1:37 PM, Tomi
>>>> Valkeinen<tomi.valkeinen@ti.com>  wrote:
>>>
>>>>> All OMAP4 versions seem to be affected. I couldn't find a mention
>>>>> about
>>>>> this in the mainline kernel. Any ideas how and where this should be
>>>>> fixed?
>>>>>
>>>> It's not patched for mainline. Generally clock-domain code
>>>> is abstracted from drivers but considering the errata and affected
>>>> modules, I guees it should be handled by DSS driver
>>>> since that is where the state of DSS or ISS will be known. Note
>>>> ISS will be automatically taken care since it will always use disaplay.
>>>>
>>>> In internal tree's this was handled as part of DSS early suspend/resume
>>>
>>> That version doesn't work as it uses functions that are not exported to
>>> drivers.
>>>
>>> I don't know much about the clock domain code, but I hope there's a way
>>> to handle it there. Otherwise I guess I need to add a new set of
>>> platform callback functions, so that the dss driver can call
>>> arch/arm/mach-omap2 code to enable and disable the work-around. I
>>> dislike that because I'm currently trying to remove those kinds of hacks
>>> to make dss work better with DT =).
>>>
>> I agree. In fact I faced similar issue when I briefly tried moving
>> OMAP cpuidle code to drivers/idle/*.
>>
>> That time me and Kevin concluded that till we move the powerdomain,
>> clockdomain code to drivers/* and export it, the cpuidle movement
>> needs to be deferred.
> 
> How about preventing the issue to occur by keeping DSS and ISS in
> No-standby mode for the affected OMAP versions. The errata says:
> 
> "Such a situation can occur when the impacted initiator is generating
> short MStandby pulses (pulse durations less than one L4 clock cycle)"
> 
> Chaning the mstandby hwmod data for DSS and ISS would prevent the need
> for exporting these clock domain functions only for this errata.
> 
That will just break PM :-)

With this change DSS will never assert standby and then PRCM can never
send idle-req to modules. Indirectly no power transitions.

Regards
Santosh