On 5/27/2011 2:46 PM, Valkeinen, Tomi wrote:
On Fri, 2011-05-27 at 14:38 +0200, Cousson, Benoit wrote:
Hi Tomi,
On 5/27/2011 9:38 AM, Valkeinen, Tomi wrote:
Add omap_device_reset() function which can be used to reset the hwmods
associated with the given platform device.
We've never exposed it because we are trying to avoid that any driver
play with asynchronous HW reset. That can lead to undefined HW behavior :-(
Do you have some strong need for that?
DSS driver has been designed so that it resets the HW before it begins
programming it. That way we get the HW into known state. Otherwise we
need to be extra careful to program all possible registers to a sane
value. Not impossible, of course, but requires extra work.
I noticed the problem with DSI driver, it didn't work anymore if I
didn't reset it.
Why does it lead to undefined HW behaviour? Isn't it much better to
reset the HW before starting to use it to be 100% sure it's in known and
valid state?
In theory, but since your are resetting only the DSS IP, it can leads to
side effect at SoC level. Especially wrt to clock management.
Especially in error situations it may be difficult (even impossible) to
recover without reset. DISPC has been known to froze in some sync lost
situations, and, if I recall right, if DSI transfer is aborted the only
way to recover is to reset the DSI block (on OMAP3).
In case of recovery error it makes sense. What we did with hardreset is
to re-assert the reset upon disable of the module and then the next
enable will de-assert it. Softreset does not do that today.
My only concern is that people might start abusing that kind of API to
use that for funtionnal purpose instead of error recovery.
This other issue is that it will add another OMAP specific IP to the driver.
Benoit
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