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Subject: Re: [PATCH stable v5.10 0/7] arm64: Default to 32-bit wide ZONE_DMA
To:     Greg KH <gregkh@linuxfoundation.org>,
        Jing Xiangfeng <jingxiangfeng@huawei.com>
CC:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        <catalin.marinas@arm.com>, <will@kernel.org>,
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From:   Kefeng Wang <wangkefeng.wang@huawei.com>
Message-ID: <31cd8432-2466-555d-7617-ae48cbcd4244@huawei.com>
Date:   Tue, 11 May 2021 20:35:47 +0800
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On 2021/3/8 17:58, Greg KH wrote:
> On Mon, Mar 08, 2021 at 11:20:03AM +0800, Jing Xiangfeng wrote:
>>
>>
>> On 2021/3/7 23:24, Greg KH wrote:
>>> On Thu, Mar 04, 2021 at 04:09:28PM +0100, Nicolas Saenz Julienne wrote:
>>>> On Thu, 2021-03-04 at 15:17 +0100, Greg KH wrote:
>>>>> On Thu, Mar 04, 2021 at 03:05:32PM +0100, Nicolas Saenz Julienne wrote:
>>>>>> Hi Greg.
>>>>>>
>>>>>> On Thu, 2021-03-04 at 14:46 +0100, Greg KH wrote:
>>>>>>> On Wed, Mar 03, 2021 at 03:33:12PM +0800, Jing Xiangfeng wrote:
>>>>>>>> Using two distinct DMA zones turned out to be problematic. Here's an
>>>>>>>> attempt go back to a saner default.
>>>>>>> What problem does this solve?  How does this fit into the stable kernel
>>>>>>> rules?
>>>>>> We changed the way we setup memory zones in arm64 in order to cater for
>>>>>> Raspberry Pi 4's weird DMA constraints: ZONE_DMA spans the lower 1GB of memory
>>>>>> and ZONE_DMA32 the rest of the 32bit address space. Since you can't allocate
>>>>>> memory that crosses zone boundaries, this broke crashkernel allocations on big
>>>>>> machines. This series fixes all this by parsing the HW description and checking
>>>>>> for DMA constrained buses. When not found, the unnecessary zone creation is
>>>>>> skipped.
>>>>> What kernel/commit caused this "breakage"?
>>>> 1a8e1cef7603 arm64: use both ZONE_DMA and ZONE_DMA32
>>> Thanks for the info, all now queued up.
>> There is a fix in 5.11. Please consider applying the following commit to
>> 5.10.y:
>>
>> aed5041ef9a3 of: unittest: Fix build on architectures without
>> CONFIG_OF_ADDRES
> 
> Thanks, now queued up.

Hi Grep, another commit d78050ee3544 "arm64: Remove 
arm64_dma32_phys_limit and its uses" should be involved, thanks.

"Prior to this patch, disabling CONFIG_ZONE_DMA32 leads to CMA
allocation from the whole RAM as arm64_dma32_phys_limit becomes
PHYS_MASK+1." from Catalin, see more from the link
https://www.spinics.net/lists/arm-kernel/msg867356.html
> 
> greg k-h
> .
>