linux-kernel - Re: [PATCH] ACPI/IORT: Fix iort_node_get

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Message-ID: <5188b273a0d8fcb035cfbb1e64ffeefb@codeaurora.org>
Date:   Mon, 09 Jan 2017 06:20:57 -0500
From:   okaya@...eaurora.org
To:     Hanjun Guo <hanjun.guo@...aro.org>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tomasz Nowicki <tn@...ihalf.com>,
        Nate Watterson <nwatters@...eaurora.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH] ACPI/IORT: Fix iort_node_get_id() mapping entries
 indexing

On 2017-01-09 01:34, Hanjun Guo wrote:
> Hi Sinan,
> 
> On 2017/1/8 5:09, Sinan Kaya wrote:
>> On 1/5/2017 1:29 PM, Lorenzo Pieralisi wrote:
>>> Commit 618f535a6062 ("ACPI/IORT: Add single mapping function")
>>> introduced a function (iort_node_get_id()) to retrieve ids for IORT
>>> named components.
>>> 
>>> iort_node_get_id() takes an index as input to refer to a specific
>>> mapping entry in the mapping array to retrieve the id at a specific
>>> index provided the index is below the total mapping count; currently 
>>> the
>>> index is used to retrieve the mapping value from the correct entry 
>>> but
>>> not to dereference the correct entry while retrieving the mapping
>>> output_reference (ie IORT parent pointer), which consequently always
>>> resolves to the output_reference of the first entry in the mapping
>>> array.
>>> 
>>> Update the map array entry pointer computation in iort_node_get_id() 
>>> to
>>> take into account the index value, fixing the issue.
>>> 
>>> Fixes: 618f535a6062 ("ACPI/IORT: Add single mapping function")
>>> Reported-by: Hanjun Guo <hanjun.guo@...aro.org>
>>> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
>>> Cc: Hanjun Guo <hanjun.guo@...aro.org>
>>> Cc: Sinan Kaya <okaya@...eaurora.org>
>>> Cc: Tomasz Nowicki <tn@...ihalf.com>
>>> Cc: Nate Watterson <nwatters@...eaurora.org>
>>> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
>>> ---
>>>  drivers/acpi/arm64/iort.c | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>> 
>>> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
>>> index e0d2e6e..ba156c5 100644
>>> --- a/drivers/acpi/arm64/iort.c
>>> +++ b/drivers/acpi/arm64/iort.c
>>> @@ -333,7 +333,7 @@ struct acpi_iort_node *iort_node_get_id(struct 
>>> acpi_iort_node *node,
>>>  		return NULL;
>>> 
>>>  	map = ACPI_ADD_PTR(struct acpi_iort_id_mapping, node,
>>> -			   node->mapping_offset);
>>> +			   node->mapping_offset + index * sizeof(*map));
>> 
>> What does this give us that the previous code didn't do?
> 
> Fir example, if you have multi mappings ids under platform device:
> 
> |-------------|
> |  SMMU  2    |<-------
> |-------------|       |
>                       |
>                       |
> |-------------|       |
> |  SMMU 1     |<----  |
> |-------------|    |  |
>                    |  |
>                    |  |
> |-------------|    |  |
> |  platform   |    |  |
> |  device     |    |  |
> |-------------|    |  |
> | stream id   |    |  |
> | 1           |    |  |
> | parent------|----|  |
> |-------------|       |
> |  stream id  |       |
> |  2          |       |
> |  parent-----|-------|
> |-------------|
> 
> For now, we just use the first entry in the mapping entry to get
> the parent, and always point to the same parent, as above, we will
> always map to SMMU 1 even if you connect to different SMMUs. (Although
> we may don't have such device topology yet)

I see. This wasn't obvious from the commit message. Thanks for taking 
time to explain it.

I think the commit message needs to include some of your description.

> 
> 
>> 
>> You are using map as a pointer and returning the offset of the first 
>> map entry above
>> and then accessing the map at the indexed offset with map[index]
>> 
>> The new code is using map as a plain pointer, calculating the pointer 
>> location with ACPI_ADD_PTR
>> instead and then collecting the output parameter with 
>> map->output_base.
>> 
>>> 
>>>  	/* Firmware bug! */
>>>  	if (!map->output_reference) {
>>> @@ -348,10 +348,10 @@ struct acpi_iort_node *iort_node_get_id(struct 
>>> acpi_iort_node *node,
>>>  	if (!(IORT_TYPE_MASK(parent->type) & type_mask))
>>>  		return NULL;
>>> 
>>> -	if (map[index].flags & ACPI_IORT_ID_SINGLE_MAPPING) {
>>> +	if (map->flags & ACPI_IORT_ID_SINGLE_MAPPING) {
>>>  		if (node->type == ACPI_IORT_NODE_NAMED_COMPONENT ||
>>>  		    node->type == ACPI_IORT_NODE_PCI_ROOT_COMPLEX) {
>>> -			*id_out = map[index].output_base;
>>> +			*id_out = map->output_base;
>> 
>> You are claiming that the existing code is collecting the output 
>> parameter from the first mapping.
>> I don't see this happening above.
>> 
>> What am I missing?
> 
> It's not about the output id but it's about the parent returned
> by this function, it always return the first entry's parent in the
> mapping entry.

Ok, I was judt looking at the patch. I didn't realize ww are changing 
the return value.

This could have been mentioned.


> 
>> 
>>>  			return parent;
>>>  		}
>>>  	}
>>> 
>> 
>> If we are just doing a housekeeping, this is fine. I couldn't see an 
>> actual bug getting fixed.
> 
> Although we may don't have such use cases for now, but I think we
> need to prepare for it, it worth a bugfix I think :)
> 
> Thanks
> Hanjun