iommu/arm-smmu-qcom: Request direct mapping for modem device
Subsystems (2)
PATCH v5 1/1 iommu/arm-smmu-qcom: Request direct mapping for modem device
The modem remote processor has two modes of access to the DDR, a direct mode and through a SMMU which requires direct mapping. The configuration of the modem SIDs is handled in TrustZone. On platforms where TrustZone is absent this needs to be explicitly done from kernel. Add compatibles for modem to opt in for direct mapping on such platforms.
---
V5
* Reword commit message and drop unnecessary details
drivers/iommu/arm-smmu-qcom.c | 2 ++ 1 file changed, 2 insertions(+)
drivers/iommu/arm-smmu-qcom.c +2 -0
@@ -17,7 +17,9 @@ static const struct of_device_id qcom_smmu_client_of_match[] = { { .compatible = "qcom,mdp4" }, { .compatible = "qcom,mdss" }, { .compatible = "qcom,sc7180-mdss" }, + { .compatible = "qcom,sc7180-mss-pil" }, { .compatible = "qcom,sdm845-mdss" }, + { .compatible = "qcom,sdm845-mss-pil" }, { } };
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Quoting Sibi Sankar (2020-05-07 12:21:57)
Quoted 3 lines
The modem remote processor has two modes of access to the DDR, a direct mode and through a SMMU which requires direct mapping. The configuration of the modem SIDs is handled in TrustZone.
Is it "The configuration of the modem SIDs is typically handled by code running in the ARM CPU's secure mode, i.e. secure EL1"? And is that even true? I though it was programmed by EL2.
Quoted 1 line
On platforms where TrustZone
TrustZone is always there.
Quoted 4 lines
is absent this needs to be explicitly done from kernel. Add compatibles for modem to opt in for direct mapping on such platforms.
Signed-off-by Sai Prakash Ranjan <[email protected]>
Is Sai the author? Or does this need a co-developed-by tag?
Quoted 5 lines
Signed-off-by Sibi Sankar <[email protected]>---
V5
* Reword commit message and drop unnecessary details
I don't see any improvement! Probably because I don't understand _why_ the modem needs a direct mapping. The commit text basically says "we need to do it because it isn't done in secure world sometimes". This is probably wrong what I wrote below, but I'd like to clarify to confirm my understanding. Maybe the commit text should say:
The modem remote processor has two access paths to DDR. One path is directly connected to DDR and another path goes through an SMMU. The SMMU path is configured to be a direct mapping because it's used by various peripherals in the modem subsystem. Typically this direct mapping is configured by programming modem SIDs into the SMMU when EL2 responds to a hyp call from the code that loads the modem binary in the secure world.
In certain firmware configurations, especially when the kernel is entered at EL2, we don't want secure mode to make hyp calls to program the SMMU because the kernel is in full control of the SMMU. Let's add compatibles here so that we can have the kernel program the SIDs for the modem in these cases.
Hey Stephen,
Thanks for taking time to review the patch.
Quoted 8 lines · Stephen Boyd
Quoting Sibi Sankar (2020-05-07 12:21:57)
Quoted 3 lines
The modem remote processor has two modes of access to the DDR, a direct mode and through a SMMU which requires direct mapping. The configuration of the modem SIDs is handled in TrustZone.
Is it "The configuration of the modem SIDs is typically handled by code running in the ARM CPU's secure mode, i.e. secure EL1"? And is that even true? I though it was programmed by EL2.
What I meant to say was qcom implementation of TZ or qcom proprietary bootloaders. I should have been more specific and mentioned that the configuration is done at EL2 by QHEE (Qualcomm's Hypervisor Execution Environment) before we enter the kernel.
Quoted 11 lines
Quoted 2 lines
On platforms where TrustZone
TrustZone is always there.
Quoted 4 lines
is absent this needs to be explicitly done from kernel. Add compatibles for modem to opt in for direct mapping on such platforms.
Signed-off-by Sai Prakash Ranjan <[email protected]>Is Sai the author? Or does this need a co-developed-by tag?
I decided to include Sai's S-b just to show I took back ownership of the patch from his patch series. I'll drop it in the next re-spin.
Quoted 4 lines
Quoted 4 lines
Signed-off-by Sibi Sankar <[email protected]>---
Quoted 8 lines
Quoted 2 lines
V5
* Reword commit message and drop unnecessary detailsI don't see any improvement! Probably because I don't understand _why_ the modem needs a direct mapping. The commit text basically says "we need to do it because it isn't done in secure world sometimes". This is probably wrong what I wrote below, but I'd like to clarify to confirm my understanding. Maybe the commit text should say:
Thanks for taking time to reword the commit message will use the same with a few corrections.
Quoted 5 lines
The modem remote processor has two access paths to DDR. One path is directly connected to DDR and another path goes through an SMMU. The SMMU path is configured to be a direct mapping because it's used by various peripherals in the modem subsystem.
I'll use ^^ as is.
Quoted 4 lines
Typically this direct
mapping is configured by programming modem SIDs into the SMMU when EL2 responds to a hyp call from the code that loads the modem binary in the secure world.
Typically this direct mapping is configured statically at EL2 by QHEE (Qualcomm's Hypervisor Execution Environment) before the kernel is entered.
Quoted 6 lines
In certain firmware configurations, especially when the kernel is entered at EL2, we don't want secure mode to make hyp calls to program the SMMU because the kernel is in full control of the SMMU. Let's add compatibles here so that we can have the kernel program the SIDs for the modem in these cases.
In certain firmware configuration, especially when the kernel is already in full control of the SMMU, defer programming the modem SIDs to the kernel. Let's add compatibles here so that we can have the kernel
program the SIDs for the modem in these cases.
Will/Stephen,
Let me know if the above changes are okay? I'll re-spin the patch based on your feedback.
Quoted 1 line
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Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc, is a member of Code Aurora Forum, a Linux Foundation Collaborative Project _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu