linux-kernel - Re: [PATCH 1/1] dma-contiguous: return early for dt case in dma_contiguous

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Message-ID: <4a7922c0-7696-b4f7-f212-6710f4b2720d@arm.com>
Date:   Tue, 1 Jun 2021 19:46:45 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Dong Aisheng <dongas86@...il.com>,
        Dong Aisheng <aisheng.dong@....com>
Cc:     iommu@...ts.linux-foundation.org,
        open list <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 1/1] dma-contiguous: return early for dt case in
 dma_contiguous_reserve

On 2021-05-31 10:21, Dong Aisheng wrote:
> On Tue, May 18, 2021 at 7:29 PM Dong Aisheng <aisheng.dong@....com> wrote:
>>
>> dma_contiguous_reserve() aims to support cmdline case for CMA memory
>> reserve. But if users define reserved memory in DT,
>> 'dma_contiguous_default_area' will not be 0, then it's meaningless
>> to continue to run dma_contiguous_reserve(). So we return early
>> if detect 'dma_contiguous_default_area' is unzero.
>>
>> Cc: Christoph Hellwig <hch@....de>
>> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
>> Cc: Robin Murphy <robin.murphy@....com>
>> Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> 
> Gently ping

The commit message is still wrong, and I still think the change doesn't 
achieve anything meaningful. This code is hard to make sense of either 
way because the crucial interplay between size_cmdline and 
dma_contiguous_default_area is hidden somewhere else entirely, and it 
would take a much more significant refactoring to clear that up.

Robin.

> 
> Regards
> Aisheng
> 
>> ---
>>   kernel/dma/contiguous.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
>> index 3d63d91cba5c..ebade9f43eff 100644
>> --- a/kernel/dma/contiguous.c
>> +++ b/kernel/dma/contiguous.c
>> @@ -171,6 +171,9 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
>>          phys_addr_t selected_limit = limit;
>>          bool fixed = false;
>>
>> +       if (dma_contiguous_default_area)
>> +               return;
>> +
>>          pr_debug("%s(limit %08lx)\n", __func__, (unsigned long)limit);
>>
>>          if (size_cmdline != -1) {
>> @@ -191,7 +194,7 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
>>   #endif
>>          }
>>
>> -       if (selected_size && !dma_contiguous_default_area) {
>> +       if (selected_size) {
>>                  pr_debug("%s: reserving %ld MiB for global area\n", __func__,
>>                           (unsigned long)selected_size / SZ_1M);
>>
>> --
>> 2.25.1
>>