From: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>, Joerg Roedel <joro@8bytes.org>,
Jordan Crouse <jcrouse@codeaurora.org>,
Rob Clark <robdclark@gmail.com>, Tomasz Figa <tfiga@chromium.org>,
Rajendra Nayak <rnayak@codeaurora.org>,
linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
Stephen Boyd <swboyd@chromium.org>,
iommu@lists.linux-foundation.org,
Matthias Kaehlcke <mka@chromium.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/2] iommu/arm-smmu: Allow client devices to select direct mapping
Date: Thu, 16 Apr 2020 23:13:50 +0530 [thread overview]
Message-ID: <c84cf5debc171c0744e32049c70197e7@codeaurora.org> (raw)
In-Reply-To: <fdc265e4-5a96-2def-df13-376249e16b49@arm.com>
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
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member
of Code Aurora Forum, hosted by The Linux Foundation
next prev parent reply other threads:[~2020-04-16 17:44 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 11:48 [PATCH 0/2] iommu/arm-smmu: Allow client devices to select direct mapping Sai Prakash Ranjan
2020-01-22 11:48 ` [PATCH 1/2] iommu: arm-smmu-impl: Convert to a generic reset implementation Sai Prakash Ranjan
2020-02-09 0:00 ` Bjorn Andersson
2020-02-14 2:44 ` Stephen Boyd
2020-04-16 13:33 ` Robin Murphy
2020-01-22 11:48 ` [PATCH 2/2] iommu/arm-smmu: Allow client devices to select direct mapping Sai Prakash Ranjan
2020-04-13 23:12 ` Evan Green
2020-04-14 16:18 ` Sai Prakash Ranjan
2020-04-16 13:58 ` Robin Murphy
2020-04-16 16:23 ` Sai Prakash Ranjan
2020-04-16 17:17 ` Robin Murphy
2020-04-16 17:43 ` Sai Prakash Ranjan [this message]
2020-02-04 17:42 ` [PATCH 0/2] " Sai Prakash Ranjan
2020-04-09 23:31 ` Matthias Kaehlcke
2020-04-11 9:20 ` Sai Prakash Ranjan
2020-04-13 15:12 ` Jordan Crouse
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