Hi Olav, On Wed, Aug 06, 2014 at 05:44:38PM +0100, Olav Haugan wrote: > On 8/6/2014 3:19 AM, Will Deacon wrote: > > On Mon, Aug 04, 2014 at 07:01:03PM +0100, Olav Haugan wrote: > >> The SMR registers do not exist when stream matching is not > >> supported by the hardware. Avoid writing to this register if not needed. > >> > >> Signed-off-by: Olav Haugan <ohaugan@xxxxxxxxxxxxxx> > >> --- > >> drivers/iommu/arm-smmu.c | 5 ++++- > >> 1 file changed, 4 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c > >> index c16431f..1f3a5b3 100644 > >> --- a/drivers/iommu/arm-smmu.c > >> +++ b/drivers/iommu/arm-smmu.c > >> @@ -1731,7 +1731,10 @@ static void arm_smmu_device_reset(struct arm_smmu_device *smmu) > >> > >> /* Mark all SMRn as invalid and all S2CRn as bypass */ > >> for (i = 0; i < smmu->num_mapping_groups; ++i) { > >> - writel_relaxed(~SMR_VALID, gr0_base + ARM_SMMU_GR0_SMR(i)); > >> + if (smmu->features & ARM_SMMU_FEAT_STREAM_MATCH) { > >> + writel_relaxed(~SMR_VALID, > >> + gr0_base + ARM_SMMU_GR0_SMR(i)); > >> + } > >> writel_relaxed(S2CR_TYPE_BYPASS, > >> gr0_base + ARM_SMMU_GR0_S2CR(i)); > > > > smmu->num_mapping_groups should be zero for an SMMU that doesn't include > > the SMR registers, so I don't think this change is needed. Are you seeing > > problems with real hardware? > > Yes, you are correct. However, since that is the case we wouldn't be > setting the S2CR registers to bypass then? Seems like > num_mappings_groups should be initialized regardless whether stream > matching or stream indexing is used. SMMU_IDR0.NUMSMRG specifies the > number of stream mapping register groups (Section 2.5.2 of the ARM > SMMUv1-v2 spec). So with stream indexing support this register should > still tell us how many S2CR registers exist? 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. > 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. Will -- 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