Re: [PATCH] ACPI/IORT: Fix iort_node_get_id() mapping entries indexing

[okaya]

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@xxxxxxxxxx>
> > > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> > > Cc: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
> > > Cc: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
> > > Cc: Tomasz Nowicki <tn@xxxxxxxxxxxx>
> > > Cc: Nate Watterson <nwatters@xxxxxxxxxxxxxx>
> > > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > > ---
> > >  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