Re: [PATCH v3] ACPI/IORT: Remove erroneous id_count check in iort_node_get_rmr_info()

[guanghui.fgh]

在 2023/7/18 15:52, Lorenzo Pieralisi 写道:
> [+Catalin, Will, Shameer]
>
> On Mon, Jul 17, 2023 at 07:33:45PM +0800, Guanghui Feng wrote:
> > According to the ARM IORT specifications DEN 0049 issue E,
> > the "Number of IDs" field in the ID mapping format reports
> > the number of IDs in the mapping range minus one.
> >
> > In iort_node_get_rmr_info(), we erroneously skip ID mappings
> > whose "Number of IDs" equal to 0, resulting in valid mapping
> > nodes with a single ID to map being skipped, which is wrong.
> >
> > Fix iort_node_get_rmr_info() by removing the bogus id_count
> > check.
> >
> > Fixes: 491cf4a6735a ("ACPI/IORT: Add support to retrieve IORT RMR reserved regions")
> > Signed-off-by: Guanghui Feng <guanghuifeng@xxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/acpi/arm64/iort.c | 3 ---
> >   1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> > index 3631230..56d8873 100644
> > --- a/drivers/acpi/arm64/iort.c
> > +++ b/drivers/acpi/arm64/iort.c
> > @@ -1007,9 +1007,6 @@ static void iort_node_get_rmr_info(struct acpi_iort_node *node,
> >   	for (i = 0; i < node->mapping_count; i++, map++) {
> >   		struct acpi_iort_node *parent;
> >   
> > -		if (!map->id_count)
> > -			continue;
> > -
> >   		parent = ACPI_ADD_PTR(struct acpi_iort_node, iort_table,
> >   				      map->output_reference);
> >   		if (parent != iommu)
>
> Shameer, I know this may look like overkill since the hunk we are
> removing is buggy but can you please test this patch on platforms
> with RMR to make sure we are not triggering regressions by removing
> it (by the specs that's what should be done but current firmware
> is always something to reckon with) ?
>
> Thanks,
> Lorenzo
Thanks for your response.

Firstly, I have tested iort rmr with one ID mapping and works well.

Secondly, When there is more than two id mappings, the buggly id_count 
check has no effect(for the id_count is larger than zero).