Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> writes: > On Wed, Mar 11, 2015 at 11:16:31AM +0800, James Liao wrote: >> Hi, >> >> On Tue, 2015-03-10 at 10:41 +0100, Sascha Hauer wrote: >> > On Mon, Mar 09, 2015 at 02:35:03PM -0700, Kevin Hilman wrote: >> > > Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> writes: >> > > >> > > > Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> >> > > >> > > A bit of a changelog here would be useful describing this driver, that >> > > it's only covering part of the device (e.g. power controller) with more >> > > to come, dependency on the syscon driver, etc. >> > > >> > > > +/* >> > > > + * The Infracfg unit has bus protection bits. We enable the bus protection >> > > > + * for disabled power domains so that the system does not hang when some unit >> > > > + * accesses the bus while in power down. >> > > > + */ >> > > >> > > Hmm, why don't you want to know if some device is accessing another >> > > device which is in a domain that is powered down? Seems like this is a >> > > good way to hide real bugs. >> > >> > How I understand it the system just hangs on erroneous accesses without >> > these protection bits enabled, so enabling them at least makes sure we >> > can output something. >> > I must admit though that my understanding of these bits is quite limited >> > and the only user of this driver I have available here (audio) doesn't >> > make use of these protection bits, so I can't test here. >> > >> > James, could you shed some light on this issue? >> >> I asked our designer about the bus protection feature, here is his >> response: >> >> " >> It's for unexpected signal glitch in Power switch process. >> >> During Power switch process, we have clock switch, reset, isolation >> enable/disable and power switch involved where the transition of >> asynchronous reset and isolation is the most critical one, which have >> risk to introduce a unexpected short period signal transition from >> MTCMOS’s interface to other alive HW . >> " >> >> That means it protects unexpected bus accessing from HW, not from SW. So >> it will not hide bugs from wrong SW access. > > Ok, thanks for clarifying. This means we should enable this feature > sooner or later. Since the audio driver which is likely the first user > of this driver doesn't need the protection bits I think we have some > time and can add the protection bits once the clock patches have been > merged. Sounds OK to me. But I still think it belongs in the infracfg layer, and not in the PM domain layer. Kevin -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
