On Fri, 2011-05-27 at 16:43 +0200, Cousson, Benoit wrote: > 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. Out of interest, can you tell more what problems it could cause? Can they be solved in the hwmod reset code? Also one thing to note, VENC needs a softreset after changing certain configurations, as per TRM. However, VENC doesn't use the standard syscontrol mechanism, so that cannot be done via omap_device interface anyway. > > 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. Why do you see it's abusing? I think it's a good driver design to reset the HW before starting operation. Perhaps it's true that in some cases reset could hide (or fix, in a way) a bug in the driver, but in the end what we want is a driver that works in every situation. And doing a HW reset sounds a good way to make the driver more robust. > This other issue is that it will add another OMAP specific IP to the driver. I presume IP == API. And that is true. But isn't reset functionality present in most HW blocks, and thus would it make a good addition to the generic API? Tomi -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
