From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olav Haugan Subject: Re: [PATCH v2 2/2] iommu/arm-smmu: Do not access non-existing SMR registers Date: Wed, 06 Aug 2014 16:34:09 -0700 Message-ID: <53E2BB71.9000201@codeaurora.org> References: <1407175263-10699-1-git-send-email-ohaugan@codeaurora.org> <1407175263-10699-3-git-send-email-ohaugan@codeaurora.org> <20140806101948.GD23882@arm.com> <53E25B76.6090208@codeaurora.org> <20140806173518.GG25953@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140806173518.GG25953-5wv7dgnIgG8@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Will Deacon Cc: "linux-arm-msm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: linux-arm-msm@vger.kernel.org On 8/6/2014 10:35 AM, Will Deacon wrote: > 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 >>>> --- >>>> 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. 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. > >> 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. Thanks, Olav -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation