On 8/7/2014 2:22 AM, Will Deacon wrote: > On Thu, Aug 07, 2014 at 12:34:09AM +0100, Olav Haugan wrote: >> On 8/6/2014 10:35 AM, Will Deacon wrote: >>> Hmm, I'm checking this with the architects because the TRMs aren't exactly >>> clear. The NUMSMRG works for stream-indexing (i.e. reports the number of >>> S2CRs), then all we have to do is change the above ~SMR_VALID to 0x0, since >>> those registers will be SBZP. >> >> You don't agree that we should avoid doing register writes if not >> necessarily? In general I like to avoid trying to write registers that >> is not needed so that we don't do more work than needed. > > If this was a fast-path then I'd certainly agree. However, device reset is > a pretty rare event and I'd be inclined to err on the side of code clarity > in preference to performance. > > Anyway, it turns out that we can't use NUMSMRG for this so all that's moot. > We instead need to do 1 << SMMU_IDR0.NUMSIDB, which will give us the number > of S2CRs. > >>>> As far as I can tell there are no other register telling us how many S2CR >>>> registers exist. That also brings up another point that there is no check >>>> in the code to ensure we are not trying to program more than the available >>>> S2CR registers when we use stream indexing. >>> >>> On an SMMU using stream-indexing, if the StreamID goes off the end of the >>> S2CRs that's a fairly serious hardware configuration issue which I don't >>> think Linux is in a position to handle. I agree that a warning wouldn't >>> hurt on device add/attach though. >>> >> >> Yes, I meant to protect against programming errors where someone >> specified more Stream IDs than available S2CRs. > > Sure. Could you have a go at hacking this up, please? > Yes, I'll update the patches. Thanks for clarifying how to determine the # of S2CRs. Thanks, Olav -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
