Messages in this thread | | | Date | Thu, 16 Apr 2020 23:13:50 +0530 | From | Sai Prakash Ranjan <> | Subject | Re: [PATCH 2/2] iommu/arm-smmu: Allow client devices to select direct mapping |
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Hi Robin,
On 2020-04-16 22:47, Robin Murphy wrote: > On 2020-04-16 5:23 pm, Sai Prakash Ranjan wrote: >> Hi Robin, >> >> On 2020-04-16 19:28, Robin Murphy wrote: >>> On 2020-01-22 11:48 am, Sai Prakash Ranjan wrote: >>>> From: Jordan Crouse <jcrouse@codeaurora.org> >>>> >>>> Some client devices want to directly map the IOMMU themselves >>>> instead >>>> of using the DMA domain. Allow those devices to opt in to direct >>>> mapping by way of a list of compatible strings. >>>> >>>> Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org> >>>> Co-developed-by: Sai Prakash Ranjan >>>> <saiprakash.ranjan@codeaurora.org> >>>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org> >>>> --- >>>> drivers/iommu/arm-smmu-qcom.c | 39 >>>> +++++++++++++++++++++++++++++++++++ >>>> drivers/iommu/arm-smmu.c | 3 +++ >>>> drivers/iommu/arm-smmu.h | 5 +++++ >>>> 3 files changed, 47 insertions(+) >>>> >>>> diff --git a/drivers/iommu/arm-smmu-qcom.c >>>> b/drivers/iommu/arm-smmu-qcom.c >>>> index 64a4ab270ab7..ff746acd1c81 100644 >>>> --- a/drivers/iommu/arm-smmu-qcom.c >>>> +++ b/drivers/iommu/arm-smmu-qcom.c >>>> @@ -3,6 +3,7 @@ >>>> * Copyright (c) 2019, The Linux Foundation. All rights reserved. >>>> */ >>>> +#include <linux/of_device.h> >>>> #include <linux/qcom_scm.h> >>>> #include "arm-smmu.h" >>>> @@ -11,6 +12,43 @@ struct qcom_smmu { >>>> struct arm_smmu_device smmu; >>>> }; >>>> +static const struct arm_smmu_client_match_data qcom_adreno = { >>>> + .direct_mapping = true, >>>> +}; >>>> + >>>> +static const struct arm_smmu_client_match_data qcom_mdss = { >>>> + .direct_mapping = true, >>>> +}; >>> >>> Might it make sense to group these by the desired SMMU behaviour >>> rather than (apparently) what kind of device the client happens to >>> be, >>> which seems like a completely arbitrary distinction from the SMMU >>> driver's PoV? >>> >> >> Sorry, I did not get the "grouping by the desired SMMU behaviour" >> thing. >> Could you please give some more details? > > I mean this pattern: > > device_a_data { > .thing = this; > } > > device_b_data { > .thing = this; > } > > device_c_data { > .thing = that; > } > > match[] = { > { .compatible = "A", .data = &device_a_data }, > { .compatible = "B", .data = &device_b_data }, > { .compatible = "C", .data = &device_c_data }, > }; > > ...vs. this pattern: > > do_this { > .thing = this; > } > > do_that { > .thing = that; > } > > match[] = { > { .compatible = "A", .data = &do_this }, > { .compatible = "B", .data = &do_this }, > { .compatible = "C", .data = &do_that }, > }; > > From the perspective of the thing doing the thing, grouping the data > by device is meaningless if all that matters is whether to do this or > that. The second pattern expresses that more naturally. > > Of course if every device turns out to need a unique combination of > several behaviours, then there ends up being no practical difference > except that it's probably easier to come up with nice names under the > first pattern. I guess it's up to how you see this developing in > future; whether you're likely to need fine-grained per-device control, > or don't expect it to go much beyond domain type. >
Thanks for explaining *this thing* :) I will update the patch to follow the 2nd pattern as it makes more sense to do_this or do_that directly. I'm not expecting anything other than domain type atleast for now but hey we can always add the functionality if the need arises.
Thanks, Sai
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