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

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Lorenzo Pieralisi [mailto:lpieralisi@kernel.org]
> Sent: 18 July 2023 08:52
> To: Guanghui Feng <guanghuifeng@linux.alibaba.com>
> Cc: Guohanjun (Hanjun Guo) <guohanjun@huawei.com>;
> sudeep.holla@arm.com; rafael@kernel.org; linux-acpi@vger.kernel.org;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> baolin.wang@linux.alibaba.com; alikernel-developer@linux.alibaba.com;
> will@kernel.org; catalin.marinas@arm.com; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@huawei.com>
> Subject: Re: [PATCH v3] ACPI/IORT: Remove erroneous id_count check in
> iort_node_get_rmr_info()
> 
> [+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@linux.alibaba.com>
> > ---
> >  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) ?

Yes, that is a valid fix. Unlikely it will be a problem. Anyway, I have requested
Hanjun to help with the testing as I don't have a test setup with me now.

Hanjun, please help.

Thanks,
Shameer