linux-kernel - Re: [PATCH v3] ACPI/IORT: Remove erroneous id_count check in iort_node_get_rmr

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Date:   Wed, 19 Jul 2023 17:13:10 +0800
From:   Hanjun Guo <guohanjun@...wei.com>
To:     Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Guanghui Feng <guanghuifeng@...ux.alibaba.com>
CC:     "sudeep.holla@....com" <sudeep.holla@....com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
        "alikernel-developer@...ux.alibaba.com" 
        <alikernel-developer@...ux.alibaba.com>,
        "will@...nel.org" <will@...nel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>
Subject: Re: [PATCH v3] ACPI/IORT: Remove erroneous id_count check in
 iort_node_get_rmr_info()

On 2023/7/18 16:56, Shameerali Kolothum Thodi wrote:
>> [+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@...ux.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.

Valid fix for me as well, we had a firmware bug which reported the
numbers of ID as 1 when we only have one ID mapping, so remove the
check is fine for the old firmware, but to make it sure, we need some
test before give it a pass.

> 
> Hanjun, please help.

I need some time to get it properly tested on two versions of firmware,
and get the test machine properly setup, please allow me give the
feedback next week.

Thanks
Hanjun