* [PATCH] iommu: of: skip iommu_device_list traversal in of_iommu_xlate()
@ 2020-09-23 14:53 Charan Teja Reddy
2020-09-23 16:24 ` Robin Murphy
0 siblings, 1 reply; 3+ messages in thread
From: Charan Teja Reddy @ 2020-09-23 14:53 UTC (permalink / raw)
To: joro, iommu; +Cc: Charan Teja Reddy, linux-kernel
In of_iommu_xlate(), check if iommu device is enabled before traversing
the iommu_device_list through iommu_ops_from_fwnode(). It is of no use
in traversing the iommu_device_list only to return NO_IOMMU because of
iommu device node is disabled.
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
---
drivers/iommu/of_iommu.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
index e505b91..225598c 100644
--- a/drivers/iommu/of_iommu.c
+++ b/drivers/iommu/of_iommu.c
@@ -94,9 +94,10 @@ static int of_iommu_xlate(struct device *dev,
struct fwnode_handle *fwnode = &iommu_spec->np->fwnode;
int ret;
+ if (!of_device_is_available(iommu_spec->np))
+ return NO_IOMMU;
ops = iommu_ops_from_fwnode(fwnode);
- if ((ops && !ops->of_xlate) ||
- !of_device_is_available(iommu_spec->np))
+ if (ops && !ops->of_xlate)
return NO_IOMMU;
ret = iommu_fwspec_init(dev, &iommu_spec->np->fwnode, ops);
--
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member of the Code Aurora Forum, hosted by The Linux Foundation
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] iommu: of: skip iommu_device_list traversal in of_iommu_xlate()
2020-09-23 14:53 [PATCH] iommu: of: skip iommu_device_list traversal in of_iommu_xlate() Charan Teja Reddy
@ 2020-09-23 16:24 ` Robin Murphy
2020-09-24 4:51 ` Charan Teja Kalla
0 siblings, 1 reply; 3+ messages in thread
From: Robin Murphy @ 2020-09-23 16:24 UTC (permalink / raw)
To: Charan Teja Reddy, joro, iommu; +Cc: linux-kernel
On 2020-09-23 15:53, Charan Teja Reddy wrote:
> In of_iommu_xlate(), check if iommu device is enabled before traversing
> the iommu_device_list through iommu_ops_from_fwnode(). It is of no use
> in traversing the iommu_device_list only to return NO_IOMMU because of
> iommu device node is disabled.
Well, the "use" is that it keeps the code that much smaller and simpler
to have a single path for returning this condition. This whole callstack
isn't exactly a high-performance code path to begin with, and we've
always assumed that IOMMUs present but disabled in DT would be a pretty
rare exception. Do you have a system that challenges those assumptions
and shows any benefit from this change?
Robin.
> Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
> ---
> drivers/iommu/of_iommu.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index e505b91..225598c 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -94,9 +94,10 @@ static int of_iommu_xlate(struct device *dev,
> struct fwnode_handle *fwnode = &iommu_spec->np->fwnode;
> int ret;
>
> + if (!of_device_is_available(iommu_spec->np))
> + return NO_IOMMU;
> ops = iommu_ops_from_fwnode(fwnode);
> - if ((ops && !ops->of_xlate) ||
> - !of_device_is_available(iommu_spec->np))
> + if (ops && !ops->of_xlate)
> return NO_IOMMU;
>
> ret = iommu_fwspec_init(dev, &iommu_spec->np->fwnode, ops);
>
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] iommu: of: skip iommu_device_list traversal in of_iommu_xlate()
2020-09-23 16:24 ` Robin Murphy
@ 2020-09-24 4:51 ` Charan Teja Kalla
0 siblings, 0 replies; 3+ messages in thread
From: Charan Teja Kalla @ 2020-09-24 4:51 UTC (permalink / raw)
To: Robin Murphy, joro, iommu; +Cc: linux-kernel
On 9/23/2020 9:54 PM, Robin Murphy wrote:
> On 2020-09-23 15:53, Charan Teja Reddy wrote:
>> In of_iommu_xlate(), check if iommu device is enabled before traversing
>> the iommu_device_list through iommu_ops_from_fwnode(). It is of no use
>> in traversing the iommu_device_list only to return NO_IOMMU because of
>> iommu device node is disabled.
>
> Well, the "use" is that it keeps the code that much smaller and simpler
> to have a single path for returning this condition. This whole callstack
> isn't exactly a high-performance code path to begin with, and we've
> always assumed that IOMMUs present but disabled in DT would be a pretty
> rare exception.
Fine..I thought that it is logical to return when IOMMU DT node is
disabled over code simplicity. And agree that it is not high-performance
path.
> Do you have a system that challenges those assumptions
> and shows any benefit from this change?
No, I don't have a system that challenges these assumptions.
>
> Robin.
>
>> Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
>> ---
>> drivers/iommu/of_iommu.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
>> index e505b91..225598c 100644
>> --- a/drivers/iommu/of_iommu.c
>> +++ b/drivers/iommu/of_iommu.c
>> @@ -94,9 +94,10 @@ static int of_iommu_xlate(struct device *dev,
>> struct fwnode_handle *fwnode = &iommu_spec->np->fwnode;
>> int ret;
>> + if (!of_device_is_available(iommu_spec->np))
>> + return NO_IOMMU;
>> ops = iommu_ops_from_fwnode(fwnode);
>> - if ((ops && !ops->of_xlate) ||
>> - !of_device_is_available(iommu_spec->np))
>> + if (ops && !ops->of_xlate)
>> return NO_IOMMU;
>> ret = iommu_fwspec_init(dev, &iommu_spec->np->fwnode, ops);
>>
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum, a Linux Foundation Collaborative Project
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2020-09-23 14:53 [PATCH] iommu: of: skip iommu_device_list traversal in of_iommu_xlate() Charan Teja Reddy
2020-09-23 16:24 ` Robin Murphy
2020-09-24 4:51 ` Charan Teja Kalla
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