Messages in this thread | | | Date | Wed, 20 Mar 2013 21:15:23 -0400 | From | Douglas Gilbert <> | Subject | Re: [PATCH] rtc: rtc-at91rm9200: use a variable for storing IMR |
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On 13-03-20 05:50 PM, Andrew Morton wrote: > On Fri, 15 Mar 2013 18:37:12 +0100 Nicolas Ferre <nicolas.ferre@atmel.com> wrote: > >> On some revisions of AT91 SoCs, the RTC IMR register is not working. >> Instead of elaborating a workaround for that specific SoC or IP version, >> we simply use a software variable to store the Interrupt Mask Register and >> modify it for each enabling/disabling of an interrupt. The overhead of this >> is negligible anyway. > > This description doesn't really allow me or others to work out whether > the fix should be included in 3.9 or backported into earlier kernels. > > So please, when fixing a bug do include a full description of the > user-visible effects of that bug. And your opinion regarding the > -mainline and -stable decision is always useful.
The interrupt mask register (IMR) for the RTC is broken on the AT91SAM9x5 sub-family of SoCs (good overview of the members here: http://www.eewiki.net/display/linuxonarm/AT91SAM9x5 ). The "user visible effect" is the RTC doesn't work.
That sub-family is less than two years old and only has devicetree (DT) support and came online circa lk 3.7 . The dust is yet to settle on the DT stuff at least for AT91 SoCs (translation: lots of stuff is still broken, so much that it is hard to know where to start).
The fix in the patch is pretty simple: just shadow the silicon IMR register with a variable in the driver. Some older SoCs (pre-DT) use the the rtc-at91rm9200 driver (e.g. obviously the AT91RM9200) and they should not be impacted by the change. There shouldn't be a large volume of interrupts associated with a RTC.
Compared to a relatively stable kernel subsystem like SCSI, what is happening in the ARM architecture with DT is huge and ongoing. So I think you either need new rules or suspend some of the stricter rules applied to more stable subsystems. Just my two cents worth.
Doug Gilbert
who hasn't seen that frill-necked lizard for a while
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