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Message-ID: <8e2cfde3-15fa-4e5a-02bf-0763abf10821@linux.alibaba.com>
Date:   Tue, 18 Jul 2023 16:54:36 +0800
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Subject: Re: [PATCH v3] ACPI/IORT: Remove erroneous id_count check in
 iort_node_get_rmr_info()
To:     Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc:     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@huawei.com
References: <1689593625-45213-1-git-send-email-guanghuifeng@linux.alibaba.com>
 <ZLZEq0QBBW4rcxJM@lpieralisi>
From:   "guanghui.fgh" <guanghuifeng@linux.alibaba.com>
In-Reply-To: <ZLZEq0QBBW4rcxJM@lpieralisi>
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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@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) ?
> 
> 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).